diff --git a/laf b/laf
index 0ae7eb7c7..410da165b 160000
--- a/laf
+++ b/laf
@@ -1 +1 @@
-Subproject commit 0ae7eb7c7fd40c5a3829cfddaede60f458877920
+Subproject commit 410da165bde1e7353eb46aa58481a956f2ad489b
diff --git a/src/app/app.cpp b/src/app/app.cpp
index 92a0b91f6..401da312f 100644
--- a/src/app/app.cpp
+++ b/src/app/app.cpp
@@ -359,7 +359,7 @@ void App::run()
   if (isGui()) {
 #ifdef _WIN32
     // How to interpret one finger on Windows tablets.
-    ui::Manager::getDefault()->nativeWindow()
+    ui::Manager::getDefault()->display()->nativeWindow()
       ->setInterpretOneFingerGestureAsMouseMovement(
         preferences().experimental.oneFingerAsMouseMovement());
 #endif
diff --git a/src/app/commands/cmd_fullscreen_mode.cpp b/src/app/commands/cmd_fullscreen_mode.cpp
index 3a78293c0..39cd63797 100644
--- a/src/app/commands/cmd_fullscreen_mode.cpp
+++ b/src/app/commands/cmd_fullscreen_mode.cpp
@@ -43,7 +43,7 @@ void FullscreenModeCommand::onExecute(Context* ctx)
   if (!manager)
     return;
 
-  os::Window* window = manager->nativeWindow();
+  os::Window* window = manager->display()->nativeWindow();
   ASSERT(window);
   if (!window)
     return;
diff --git a/src/app/commands/cmd_fullscreen_preview.cpp b/src/app/commands/cmd_fullscreen_preview.cpp
index 2797f04a5..6b260e87b 100644
--- a/src/app/commands/cmd_fullscreen_preview.cpp
+++ b/src/app/commands/cmd_fullscreen_preview.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -51,8 +51,13 @@ public:
     , m_pal(m_sprite->palette(editor->frame()))
     , m_proj(editor->projection())
     , m_index_bg_color(-1)
-    , m_doublebuf(Image::create(IMAGE_RGB, ui::display_w(), ui::display_h()))
-    , m_doublesur(os::instance()->makeRgbaSurface(ui::display_w(), ui::display_h())) {
+    , m_doublebuf(Image::create(
+                    IMAGE_RGB,
+                    editor->display()->size().w,
+                    editor->display()->size().h))
+    , m_doublesur(os::instance()->makeRgbaSurface(
+                    editor->display()->size().w,
+                    editor->display()->size().h)) {
     // Do not use DocWriter (do not lock the document) because we
     // will call other sub-commands (e.g. previous frame, next frame,
     // etc.).
@@ -170,6 +175,7 @@ protected:
   }
 
   virtual void onPaint(PaintEvent& ev) override {
+    gfx::Size displaySize = display()->size();
     Graphics* g = ev.graphics();
     EditorRender& render = m_editor->renderEngine();
     render.setRefLayersVisiblity(false);
@@ -213,18 +219,18 @@ protected:
                            255, BlendMode::NORMAL);
         break;
       case TiledMode::X_AXIS:
-        for (u=x-w; u<ui::display_w()+w; u+=w)
+        for (u=x-w; u<displaySize.w+w; u+=w)
           render.renderImage(m_doublebuf.get(), m_render.get(), m_pal, u, y,
                              255, BlendMode::NORMAL);
         break;
       case TiledMode::Y_AXIS:
-        for (v=y-h; v<ui::display_h()+h; v+=h)
+        for (v=y-h; v<displaySize.h+h; v+=h)
           render.renderImage(m_doublebuf.get(), m_render.get(), m_pal, x, v,
                              255, BlendMode::NORMAL);
         break;
       case TiledMode::BOTH:
-        for (v=y-h; v<ui::display_h()+h; v+=h)
-          for (u=x-w; u<ui::display_w()+w; u+=w)
+        for (v=y-h; v<displaySize.h+h; v+=h)
+          for (u=x-w; u<displaySize.w+w; u+=w)
             render.renderImage(m_doublebuf.get(), m_render.get(), m_pal, u, v,
                                255, BlendMode::NORMAL);
         break;
diff --git a/src/app/commands/cmd_keyboard_shortcuts.cpp b/src/app/commands/cmd_keyboard_shortcuts.cpp
index 9b887d85f..56df8062e 100644
--- a/src/app/commands/cmd_keyboard_shortcuts.cpp
+++ b/src/app/commands/cmd_keyboard_shortcuts.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -88,8 +88,9 @@ public:
     m_keyLabel.setStyle(theme->styles.listHeaderLabel());
     m_contextLabel.setStyle(theme->styles.listHeaderLabel());
 
-    m_splitter1.setPosition(ui::display_w()*3/4 * 4/10);
-    m_splitter2.setPosition(ui::display_w()*3/4 * 2/10);
+    gfx::Size displaySize = display()->size();
+    m_splitter1.setPosition(displaySize.w*3/4 * 4/10);
+    m_splitter2.setPosition(displaySize.w*3/4 * 2/10);
 
     addChild(&m_splitter1);
     m_splitter1.addChild(&m_actionLabel);
@@ -881,7 +882,8 @@ void KeyboardShortcutsCommand::onExecute(Context* context)
   std::string neededSearchCopy = m_search;
   KeyboardShortcutsWindow window(keys, menuKeys, neededSearchCopy);
 
-  window.setBounds(gfx::Rect(0, 0, ui::display_w()*3/4, ui::display_h()*3/4));
+  gfx::Size displaySize = ui::get_desktop_size();
+  window.setBounds(gfx::Rect(0, 0, displaySize.w*3/4, displaySize.h*3/4));
   window.loadLayout();
 
   window.centerWindow();
diff --git a/src/app/commands/cmd_options.cpp b/src/app/commands/cmd_options.cpp
index bcf5369ed..b10567409 100644
--- a/src/app/commands/cmd_options.cpp
+++ b/src/app/commands/cmd_options.cpp
@@ -725,7 +725,7 @@ public:
       m_pref.tablet.api(tabletStr);
       m_pref.experimental.loadWintabDriver(wintabState);
 
-      manager()->nativeWindow()
+      manager()->display()->nativeWindow()
         ->setInterpretOneFingerGestureAsMouseMovement(
           oneFingerAsMouseMovement()->isSelected());
 
@@ -845,10 +845,8 @@ private:
 
   void updateScreenScaling() {
     ui::Manager* manager = ui::Manager::getDefault();
-    os::Window* window = manager->nativeWindow();
     os::instance()->setGpuAcceleration(m_pref.general.gpuAcceleration());
-    window->setScale(m_pref.general.screenScale());
-    manager->setNativeWindow(window);
+    manager->updateAllDisplaysWithNewScale(m_pref.general.screenScale());
   }
 
   void onApply() {
diff --git a/src/app/commands/cmd_paste_text.cpp b/src/app/commands/cmd_paste_text.cpp
index fdbc7fb70..1619fc740 100644
--- a/src/app/commands/cmd_paste_text.cpp
+++ b/src/app/commands/cmd_paste_text.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -29,7 +29,7 @@
 #include "render/dithering.h"
 #include "render/ordered_dither.h"
 #include "render/quantization.h"
-#include "ui/system.h"
+#include "ui/manager.h"
 
 #include "paste_text.xml.h"
 
@@ -124,10 +124,11 @@ private:
     }
 
     if (!m_fontPopup->isVisible()) {
+      gfx::Size displaySize = manager()->display()->size();
       gfx::Rect bounds = fontFace()->bounds();
       m_fontPopup->showPopup(
         gfx::Rect(bounds.x, bounds.y+bounds.h,
-                  ui::display_w()/2, ui::display_h()/2));
+                  displaySize.w/2, displaySize.h/2));
     }
     else {
       m_fontPopup->closeWindow(NULL);
diff --git a/src/app/commands/cmd_undo.cpp b/src/app/commands/cmd_undo.cpp
index 53666bc32..2b7ca04ee 100644
--- a/src/app/commands/cmd_undo.cpp
+++ b/src/app/commands/cmd_undo.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2020  Igara Studio S.A.
+// Copyright (C) 2020-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -94,7 +94,7 @@ void UndoCommand::onExecute(Context* context)
       current_editor->drawSpriteClipped(
         gfx::Region(gfx::Rect(0, 0, sprite->width(), sprite->height())));
 
-      current_editor->manager()->flipDisplay();
+      current_editor->display()->flipDisplay();
       base::this_thread::sleep_for(0.01);
     }
   }
diff --git a/src/app/commands/screenshot.cpp b/src/app/commands/screenshot.cpp
index e0c5d975c..a0df48399 100644
--- a/src/app/commands/screenshot.cpp
+++ b/src/app/commands/screenshot.cpp
@@ -69,7 +69,7 @@ void ScreenshotCommand::onExecute(Context* ctx)
   app::ResourceFinder rf(false);
   rf.includeDesktopDir("");
 
-  os::Window* window = ui::Manager::getDefault()->nativeWindow();
+  os::Window* window = ui::Manager::getDefault()->display()->nativeWindow();
   os::Surface* surface = window->surface();
   std::string fn;
 
diff --git a/src/app/console.cpp b/src/app/console.cpp
index 78c1951da..242904232 100644
--- a/src/app/console.cpp
+++ b/src/app/console.cpp
@@ -70,8 +70,13 @@ public:
 
   void centerConsole() {
     initTheme();
+
     remapWindow();
-    setBounds(gfx::Rect(0, 0, ui::display_w()*9/10, ui::display_h()*6/10));
+
+    // TODO center to main window or screen workspace
+    gfx::Size displaySize = manager()->display()->size();
+    setBounds(gfx::Rect(0, 0, displaySize.w*9/10, displaySize.h*6/10));
+
     centerWindow();
     invalidate();
   }
@@ -116,14 +121,16 @@ Console::Console(Context* ctx)
   if (!ui::is_ui_thread())
     return;
 
-  if (ctx)
+  if (ctx) {
     m_withUI = (ctx->isUIAvailable());
-  else
+  }
+  else {
     m_withUI =
       (App::instance() &&
        App::instance()->isGui() &&
        Manager::getDefault() &&
-       Manager::getDefault()->nativeWindow());
+       Manager::getDefault()->display()->nativeWindow());
+  }
 
   if (!m_withUI)
     return;
diff --git a/src/app/modules/gui.cpp b/src/app/modules/gui.cpp
index 25d33ef2d..b063cd013 100644
--- a/src/app/modules/gui.cpp
+++ b/src/app/modules/gui.cpp
@@ -81,8 +81,13 @@ static struct {
 
 //////////////////////////////////////////////////////////////////////
 
-class CustomizedGuiManager : public Manager
-                           , public LayoutIO {
+class CustomizedGuiManager : public ui::Manager
+                           , public ui::LayoutIO {
+public:
+  CustomizedGuiManager(const os::WindowRef& nativeWindow)
+    : ui::Manager(nativeWindow) {
+  }
+
 protected:
   bool onProcessMessage(Message* msg) override;
 #if ENABLE_DEVMODE
@@ -90,7 +95,7 @@ protected:
 #endif
   void onInitTheme(InitThemeEvent& ev) override;
   LayoutIO* onGetLayoutIO() override { return this; }
-  void onNewDisplayConfiguration() override;
+  void onNewDisplayConfiguration(Display* display) override;
 
   // LayoutIO implementation
   std::string loadLayout(Widget* widget) override;
@@ -193,8 +198,7 @@ int init_module_gui()
   }
 
   // Create the default-manager
-  manager = new CustomizedGuiManager();
-  manager->setNativeWindow(main_window.get());
+  manager = new CustomizedGuiManager(main_window);
 
   // Setup the GUI theme for all widgets
   gui_theme = new SkinTheme;
@@ -205,17 +209,20 @@ int init_module_gui()
 
   // Handle live resize too redraw the entire manager, dispatch the UI
   // messages, and flip the window.
-  main_window->handleResize =
+  os::instance()->handleWindowResize =
     [](os::Window* window) {
-      manager->invalidate();
+      Display* display = manager->getDisplayFromNativeWindow(window);
+      if (!display)
+        display = manager->display();
+      ASSERT(display);
 
       Message* msg = new Message(kResizeDisplayMessage);
+      msg->setDisplay(display);
       msg->setRecipient(manager);
       msg->setPropagateToChildren(true);
-      manager->enqueueMessage(msg);
 
+      manager->enqueueMessage(msg);
       manager->dispatchMessages();
-      manager->flipDisplay();
     };
 
   // Set graphics options for next time
@@ -292,7 +299,7 @@ static void load_gui_config(int& w, int& h, bool& maximized,
 
 static void save_gui_config()
 {
-  os::Window* window = manager->nativeWindow();
+  os::Window* window = manager->display()->nativeWindow();
   if (window) {
     set_config_bool("GfxMode", "Maximized", window->isMaximized());
     set_config_int("GfxMode", "Width", window->originalWidth());
@@ -327,6 +334,8 @@ void update_screen_for_document(const Doc* document)
 void load_window_pos(Widget* window, const char* section,
                      const bool limitMinSize)
 {
+  Size desktopSize = ui::get_desktop_size();
+
   // Default position
   Rect orig_pos = window->bounds();
   Rect pos = orig_pos;
@@ -335,16 +344,16 @@ void load_window_pos(Widget* window, const char* section,
   pos = get_config_rect(section, "WindowPos", pos);
 
   if (limitMinSize) {
-    pos.w = base::clamp(pos.w, orig_pos.w, ui::display_w());
-    pos.h = base::clamp(pos.h, orig_pos.h, ui::display_h());
+    pos.w = base::clamp(pos.w, orig_pos.w, desktopSize.w);
+    pos.h = base::clamp(pos.h, orig_pos.h, desktopSize.h);
   }
   else {
-    pos.w = std::min(pos.w, ui::display_w());
-    pos.h = std::min(pos.h, ui::display_h());
+    pos.w = std::min(pos.w, desktopSize.w);
+    pos.h = std::min(pos.h, desktopSize.h);
   }
 
-  pos.setOrigin(Point(base::clamp(pos.x, 0, ui::display_w()-pos.w),
-                      base::clamp(pos.y, 0, ui::display_h()-pos.h)));
+  pos.setOrigin(Point(base::clamp(pos.x, 0, desktopSize.w-pos.w),
+                      base::clamp(pos.y, 0, desktopSize.h-pos.h)));
 
   window->setBounds(pos);
 }
@@ -653,9 +662,9 @@ void CustomizedGuiManager::onInitTheme(InitThemeEvent& ev)
   AppMenus::instance()->initTheme();
 }
 
-void CustomizedGuiManager::onNewDisplayConfiguration()
+void CustomizedGuiManager::onNewDisplayConfiguration(Display* display)
 {
-  Manager::onNewDisplayConfiguration();
+  Manager::onNewDisplayConfiguration(display);
   save_gui_config();
 
   // TODO Should we provide a more generic way for all ui::Window to
diff --git a/src/app/ui/color_bar.cpp b/src/app/ui/color_bar.cpp
index bc8386005..40db5d391 100644
--- a/src/app/ui/color_bar.cpp
+++ b/src/app/ui/color_bar.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -1884,12 +1884,13 @@ void ColorBar::showPalettePresets()
   }
 
   if (!m_palettePopup->isVisible()) {
+    gfx::Size displaySize = ui::get_desktop_size();
     gfx::Rect bounds = m_buttons.getItem(
       static_cast<int>(PalButton::PRESETS))->bounds();
 
     m_palettePopup->showPopup(
       gfx::Rect(bounds.x, bounds.y+bounds.h,
-                ui::display_w()/2, ui::display_h()*3/4));
+                displaySize.w/2, displaySize.h*3/4));
   }
   else {
     m_palettePopup->closeWindow(NULL);
diff --git a/src/app/ui/color_button.cpp b/src/app/ui/color_button.cpp
index 3692c3bc1..73f5df230 100644
--- a/src/app/ui/color_button.cpp
+++ b/src/app/ui/color_button.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2020  Igara Studio S.A.
+// Copyright (C) 2020-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -302,12 +302,13 @@ void ColorButton::openPopup(const bool forcePinned)
   m_window->setColor(m_color, ColorPopup::ChangeType);
   m_window->openWindow();
 
+  gfx::Size displaySize = ui::get_desktop_size();
   gfx::Rect winBounds;
   if (!pinned || (forcePinned && m_hiddenPopupBounds.isEmpty())) {
     winBounds = gfx::Rect(m_window->bounds().origin(),
                           m_window->sizeHint());
-    winBounds.x = base::clamp(bounds().x, 0, ui::display_w()-winBounds.w);
-    if (bounds().y2() <= ui::display_h()-winBounds.h)
+    winBounds.x = base::clamp(bounds().x, 0, displaySize.w-winBounds.w);
+    if (bounds().y2() <= displaySize.h-winBounds.h)
       winBounds.y = std::max(0, bounds().y2());
     else
       winBounds.y = std::max(0, bounds().y-winBounds.h);
@@ -318,8 +319,8 @@ void ColorButton::openPopup(const bool forcePinned)
   else {
     winBounds = m_windowDefaultBounds;
   }
-  winBounds.x = base::clamp(winBounds.x, 0, ui::display_w()-winBounds.w);
-  winBounds.y = base::clamp(winBounds.y, 0, ui::display_h()-winBounds.h);
+  winBounds.x = base::clamp(winBounds.x, 0, displaySize.w-winBounds.w);
+  winBounds.y = base::clamp(winBounds.y, 0, displaySize.h-winBounds.h);
   m_window->setBounds(winBounds);
 
   m_window->manager()->dispatchMessages();
diff --git a/src/app/ui/draggable_widget.h b/src/app/ui/draggable_widget.h
index ebcdd6461..1c6e7f74f 100644
--- a/src/app/ui/draggable_widget.h
+++ b/src/app/ui/draggable_widget.h
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
@@ -147,14 +147,16 @@ private:
       paint.style(os::Paint::Fill);
       surface->drawRect(gfx::Rect(0, 0, surface->width(), surface->height()), paint);
     }
+
+    ui::Display* display = this->Base::display();
     {
-      ui::Graphics g(surface, 0, 0);
+      ui::Graphics g(display, surface, 0, 0);
       g.setFont(AddRef(this->font()));
       drawFloatingOverlay(g);
     }
 
     m_floatingOverlay = base::make_ref<ui::Overlay>(
-      surface, gfx::Point(),
+      display, surface, gfx::Point(),
       (ui::Overlay::ZOrder)(ui::Overlay::MouseZOrder-1));
     ui::OverlayManager::instance()->addOverlay(m_floatingOverlay);
   }
diff --git a/src/app/ui/editor/brush_preview.cpp b/src/app/ui/editor/brush_preview.cpp
index cfee3160b..56c726695 100644
--- a/src/app/ui/editor/brush_preview.cpp
+++ b/src/app/ui/editor/brush_preview.cpp
@@ -349,7 +349,7 @@ void BrushPreview::show(const gfx::Point& screenPos)
   // Save area and draw the cursor
   if (!(m_type & NATIVE_CROSSHAIR) ||
       (m_type & BRUSH_BOUNDARIES)) {
-    ui::ScreenGraphics g;
+    ui::ScreenGraphics g(m_editor->display());
     ui::SetClip clip(&g);
     gfx::Color uiCursorColor = color_utils::color_for_ui(appCursorColor);
     forEachBrushPixel(&g, m_screenPosition, spritePos, uiCursorColor, &BrushPreview::savePixelDelegate);
@@ -387,7 +387,7 @@ void BrushPreview::hide()
 
   if (m_withModifiedPixels) {
     // Restore pixels
-    ui::ScreenGraphics g;
+    ui::ScreenGraphics g(m_editor->display());
     ui::SetClip clip(&g);
     forEachBrushPixel(&g, m_screenPosition, m_editorPosition, gfx::ColorNone,
                       &BrushPreview::clearPixelDelegate);
diff --git a/src/app/ui/editor/editor.cpp b/src/app/ui/editor/editor.cpp
index 1c2b173ac..cf3e0eece 100644
--- a/src/app/ui/editor/editor.cpp
+++ b/src/app/ui/editor/editor.cpp
@@ -947,7 +947,7 @@ void Editor::drawSpriteClipped(const gfx::Region& updateRegion)
   Region screenRegion;
   getDrawableRegion(screenRegion, kCutTopWindows);
 
-  ScreenGraphics screenGraphics;
+  ScreenGraphics screenGraphics(display());
   GraphicsPtr editorGraphics = getGraphics(clientBounds());
 
   for (const Rect& updateRect : updateRegion) {
@@ -1163,7 +1163,6 @@ void Editor::drawTileNumbers(ui::Graphics* g, const Cel* cel)
     int ti_offset =
       static_cast<LayerTilemap*>(cel->layer())->tileset()->baseIndex() - 1;
 
-    const gfx::Rect rc = cel->bounds();
     const doc::Image* image = cel->image();
     std::string text;
     for (int y=0; y<image->height(); ++y) {
diff --git a/src/app/ui/editor/standby_state.cpp b/src/app/ui/editor/standby_state.cpp
index facfcabf8..c8300099e 100644
--- a/src/app/ui/editor/standby_state.cpp
+++ b/src/app/ui/editor/standby_state.cpp
@@ -1029,7 +1029,7 @@ void StandbyState::Decorator::postRenderDecorator(EditorPostRender* render)
   if (StandbyState::Decorator::getSymmetryHandles(editor, handles)) {
     skin::SkinTheme* theme = static_cast<skin::SkinTheme*>(ui::get_theme());
     os::Surface* part = theme->parts.transformationHandle()->bitmap(0);
-    ScreenGraphics g;
+    ScreenGraphics g(editor->display());
     for (const auto& handle : handles)
       g.drawRgbaSurface(part, handle.bounds.x, handle.bounds.y);
   }
diff --git a/src/app/ui/editor/zooming_state.cpp b/src/app/ui/editor/zooming_state.cpp
index fa99a0e33..b9c132c7b 100644
--- a/src/app/ui/editor/zooming_state.cpp
+++ b/src/app/ui/editor/zooming_state.cpp
@@ -67,7 +67,7 @@ bool ZoomingState::onMouseUp(Editor* editor, MouseMessage* msg)
 bool ZoomingState::onMouseMove(Editor* editor, MouseMessage* msg)
 {
   gfx::Point pt = (msg->position() - m_startPos);
-  int threshold = 8 * guiscale() * editor->manager()->nativeWindow()->scale();
+  int threshold = 8 * guiscale() * editor->display()->nativeWindow()->scale();
 
   if (m_moved || std::sqrt(pt.x*pt.x + pt.y*pt.y) > threshold) {
     m_moved = true;
diff --git a/src/app/ui/file_selector.cpp b/src/app/ui/file_selector.cpp
index 3249bbce8..06eb04302 100644
--- a/src/app/ui/file_selector.cpp
+++ b/src/app/ui/file_selector.cpp
@@ -421,7 +421,8 @@ bool FileSelector::show(
 
   FILESEL_TRACE("FILESEL: Start folder '%s' (%p)\n", start_folder_path.c_str(), start_folder);
 
-  setMinSize(gfx::Size(ui::display_w()*9/10, ui::display_h()*9/10));
+  gfx::Size displaySize = ui::get_desktop_size();
+  setMinSize(gfx::Size(displaySize.w*9/10, displaySize.h*9/10));
   remapWindow();
   centerWindow();
 
diff --git a/src/app/ui/main_window.cpp b/src/app/ui/main_window.cpp
index defb46db6..50b108d8a 100644
--- a/src/app/ui/main_window.cpp
+++ b/src/app/ui/main_window.cpp
@@ -77,10 +77,8 @@ public:
 
     ui::set_theme(ui::get_theme(), newUIScale);
 
-    Manager* manager = Manager::getDefault();
-    os::Window* window = manager->nativeWindow();
-    window->setScale(newScreenScale);
-    manager->setNativeWindow(window);
+    Manager::getDefault()
+      ->updateAllDisplaysWithNewScale(newScreenScale);
   }
 };
 
@@ -370,12 +368,13 @@ void MainWindow::onResize(ui::ResizeEvent& ev)
 {
   app::gen::MainWindow::onResize(ev);
 
-  os::Window* window = manager()->nativeWindow();
-  if ((window) &&
-      (window->scale()*ui::guiscale() > 2) &&
+  gfx::Size desktopSize = ui::get_desktop_size();
+  ui::Display* display = this->display();
+  if ((display) &&
+      (display->nativeWindow()->scale()*ui::guiscale() > 2) &&
       (!m_scalePanic) &&
-      (ui::display_w()/ui::guiscale() < 320 ||
-       ui::display_h()/ui::guiscale() < 260)) {
+      (desktopSize.w/ui::guiscale() < 320 ||
+       desktopSize.h/ui::guiscale() < 260)) {
     showNotification(m_scalePanic = new ScreenScalePanic);
   }
 }
diff --git a/src/app/ui/preview_editor.cpp b/src/app/ui/preview_editor.cpp
index e591ebd5b..4759c72f5 100644
--- a/src/app/ui/preview_editor.cpp
+++ b/src/app/ui/preview_editor.cpp
@@ -224,13 +224,14 @@ bool PreviewEditorWindow::onProcessMessage(ui::Message* msg)
         SkinTheme* theme = SkinTheme::instance();
 
         // Default bounds
-        int width = ui::display_w()/4;
-        int height = ui::display_h()/4;
+        gfx::Size desktopSize = ui::get_desktop_size();
+        const int width = desktopSize.w/4;
+        const int height = desktopSize.h/4;
         int extra = 2*theme->dimensions.miniScrollbarSize();
         setBounds(
           gfx::Rect(
-            ui::display_w() - width - ToolBar::instance()->bounds().w - extra,
-            ui::display_h() - height - StatusBar::instance()->bounds().h - extra,
+            desktopSize.w - width - ToolBar::instance()->bounds().w - extra,
+            desktopSize.h - height - StatusBar::instance()->bounds().h - extra,
             width, height));
 
         load_window_pos(this, "MiniEditor", false);
diff --git a/src/app/ui/tabs.cpp b/src/app/ui/tabs.cpp
index d14eeed69..82bee8719 100644
--- a/src/app/ui/tabs.cpp
+++ b/src/app/ui/tabs.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This program is distributed under the terms of
@@ -941,6 +941,7 @@ void Tabs::createFloatingOverlay(Tab* tab)
 {
   ASSERT(!m_floatingOverlay);
 
+  ui::Display* display = this->display();
   os::SurfaceRef surface = os::instance()->makeRgbaSurface(
     tab->width, m_tabsHeight);
 
@@ -953,13 +954,13 @@ void Tabs::createFloatingOverlay(Tab* tab)
     surface->drawRect(gfx::Rect(0, 0, surface->width(), surface->height()), paint);
   }
   {
-    Graphics g(surface, 0, 0);
+    Graphics g(display, surface, 0, 0);
     g.setFont(AddRef(font()));
     drawTab(&g, g.getClipBounds(), tab, 0, true, true);
   }
 
   m_floatingOverlay = base::make_ref<ui::Overlay>(
-    surface, gfx::Point(),
+    display, surface, gfx::Point(),
     (ui::Overlay::ZOrder)(Overlay::MouseZOrder-1));
   OverlayManager::instance()->addOverlay(m_floatingOverlay);
 }
diff --git a/src/app/ui/timeline/timeline.cpp b/src/app/ui/timeline/timeline.cpp
index 12d7f4cca..74966bd63 100644
--- a/src/app/ui/timeline/timeline.cpp
+++ b/src/app/ui/timeline/timeline.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -1242,7 +1242,7 @@ bool Timeline::onProcessMessage(Message* msg)
 
             if (!m_confPopup->isVisible()) {
               gfx::Rect bounds = m_confPopup->bounds();
-              ui::fit_bounds(BOTTOM, gearBounds, bounds);
+              ui::fit_bounds(display(), BOTTOM, gearBounds, bounds);
 
               m_confPopup->moveWindow(bounds);
               m_confPopup->openWindow();
diff --git a/src/app/ui/toolbar.cpp b/src/app/ui/toolbar.cpp
index 5bb21e40c..c819c6bd2 100644
--- a/src/app/ui/toolbar.cpp
+++ b/src/app/ui/toolbar.cpp
@@ -530,7 +530,8 @@ void ToolBar::openTipWindow(int group_index, Tool* tool)
   if (tool && m_popupWindow && m_popupWindow->isVisible())
     toolrc.x += arrow.x - m_popupWindow->bounds().w;
 
-  m_tipWindow->pointAt(TOP | RIGHT, toolrc);
+  m_tipWindow->pointAt(TOP | RIGHT, toolrc,
+                       ui::Manager::getDefault()->display());
 
   if (m_tipOpened)
     m_tipWindow->openWindow();
diff --git a/src/tests/test.h b/src/tests/test.h
index 1d2d746c8..00b396183 100644
--- a/src/tests/test.h
+++ b/src/tests/test.h
@@ -40,7 +40,7 @@ int main(int argc, char* argv[])
       // Do not create a os::System, as we don't need it for testing purposes.
       //os::ScopedHandle<os::System> system(os::create_system());
       ui::UISystem uiSystem;
-      ui::Manager uiManager;
+      ui::Manager uiManager(nullptr);
   #endif
 
       exitcode = RUN_ALL_TESTS();
diff --git a/src/ui/CMakeLists.txt b/src/ui/CMakeLists.txt
index a2db7bb6c..563aa9b58 100644
--- a/src/ui/CMakeLists.txt
+++ b/src/ui/CMakeLists.txt
@@ -1,4 +1,5 @@
 # Aseprite UI Library
+# Copyright (C) 2019  Igara Studio S.A.
 # Copyright (C) 2001-2018  David Capello
 
 if(WIN32)
@@ -13,6 +14,7 @@ add_library(ui-lib
   combobox.cpp
   component.cpp
   cursor.cpp
+  display.cpp
   entry.cpp
   event.cpp
   fit_bounds.cpp
diff --git a/src/ui/combobox.cpp b/src/ui/combobox.cpp
index 71de76dcb..fa95fd067 100644
--- a/src/ui/combobox.cpp
+++ b/src/ui/combobox.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -614,8 +614,12 @@ void ComboBox::openListBox()
   m_window = new Window(Window::WithoutTitleBar);
   View* view = new View();
   m_listbox = new ComboBoxListBox(this);
+  // TODO create a real native window for comboboxes
+  m_window->setDisplay(display());
   m_window->setOnTop(true);
   m_window->setWantFocus(false);
+  m_window->setSizeable(false);
+  m_window->setMoveable(false);
 
   Widget* viewport = view->viewport();
   {
@@ -627,8 +631,10 @@ void ComboBox::openListBox()
       if (!item->hasFlags(HIDDEN))
         size.h += item->sizeHint().h;
 
-    int max = std::max(entryBounds.y, ui::display_h() - entryBounds.y2()) - 8*guiscale();
-    size.h = base::clamp(size.h, textHeight(), max);
+    const int maxVal =
+      std::max(entryBounds.y, display()->size().h - entryBounds.y2())
+      - 8*guiscale();
+    size.h = base::clamp(size.h, textHeight(), maxVal);
     viewport->setMinSize(size);
   }
 
@@ -688,7 +694,7 @@ gfx::Rect ComboBox::getListBoxPos() const
                gfx::Point(m_button->bounds().x2(),
                           entryBounds.y2() + m_window->bounds().h));
 
-  if (rc.y2() > ui::display_h())
+  if (rc.y2() > display()->size().h)
     rc.offset(0, -(rc.h + entryBounds.h));
 
   return rc;
diff --git a/src/ui/display.cpp b/src/ui/display.cpp
new file mode 100644
index 000000000..e24f3a9f3
--- /dev/null
+++ b/src/ui/display.cpp
@@ -0,0 +1,114 @@
+// Aseprite UI Library
+// Copyright (C) 2019-2021  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "ui/display.h"
+
+#include "base/debug.h"
+#include "ui/widget.h"
+#include "ui/window.h"
+
+#include <algorithm>
+
+namespace ui {
+
+Display::Display(const os::WindowRef& nativeWindow,
+                 Widget* containedWidget)
+  : m_nativeWindow(nativeWindow)
+  , m_containedWidget(containedWidget)
+{
+  ASSERT(m_nativeWindow);
+  ASSERT(m_containedWidget);
+  ASSERT(m_containedWidget->type() == kManagerWidget ||
+         m_containedWidget->type() == kWindowWidget);
+  m_dirtyRegion = bounds();
+}
+
+os::Surface* Display::surface() const
+{
+  return m_nativeWindow->surface();
+}
+
+gfx::Size Display::size() const
+{
+  ASSERT(m_nativeWindow);
+  const int scale = m_nativeWindow->scale();
+  ASSERT(scale > 0);
+  return gfx::Size(m_nativeWindow->width() / scale,
+                   m_nativeWindow->height() / scale);
+}
+
+void Display::dirtyRect(const gfx::Rect& bounds)
+{
+  m_dirtyRegion.createUnion(m_dirtyRegion, gfx::Region(bounds));
+}
+
+void Display::flipDisplay()
+{
+  if (!m_dirtyRegion.isEmpty()) {
+    // Limit the region to the bounds of the window
+    m_dirtyRegion &= gfx::Region(bounds());
+
+    if (!m_dirtyRegion.isEmpty()) {
+      // Invalidate the dirty region in the os::Window
+      m_nativeWindow->invalidateRegion(m_dirtyRegion);
+      m_dirtyRegion.clear();
+    }
+  }
+}
+
+void Display::invalidateRect(const gfx::Rect& rect)
+{
+  m_containedWidget->invalidateRect(rect);
+}
+
+void Display::invalidateRegion(const gfx::Region& region)
+{
+  m_containedWidget->invalidateRegion(region);
+}
+
+void Display::addWindow(Window* window)
+{
+  m_windows.insert(m_windows.begin(), window);
+}
+
+void Display::removeWindow(Window* window)
+{
+  auto it = std::find(m_windows.begin(), m_windows.end(), window);
+  ASSERT(it != m_windows.end())
+  if (it == m_windows.end())
+    return;
+
+  m_windows.erase(it);
+}
+
+// TODO code similar to Manager::handleWindowZOrder()
+void Display::handleWindowZOrder(Window* window)
+{
+  removeWindow(window);
+
+  if (window->isOnTop())
+    m_windows.insert(m_windows.begin(), window);
+  else {
+    int pos = (int)m_windows.size();
+
+    for (auto it=m_windows.rbegin(),
+           end=m_windows.rend();
+         it != end; ++it) {
+      if (static_cast<Window*>(*it)->isOnTop())
+        break;
+
+      --pos;
+    }
+
+    m_windows.insert(m_windows.begin()+pos, window);
+  }
+}
+
+} // namespace ui
diff --git a/src/ui/display.h b/src/ui/display.h
new file mode 100644
index 000000000..ad84bfc44
--- /dev/null
+++ b/src/ui/display.h
@@ -0,0 +1,83 @@
+// Aseprite UI Library
+// Copyright (C) 2019-2021  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef UI_DISPLAY_H_INCLUDED
+#define UI_DISPLAY_H_INCLUDED
+#pragma once
+
+#include "gfx/rect.h"
+#include "gfx/region.h"
+#include "gfx/size.h"
+#include "os/window.h"
+
+#include <vector>
+
+namespace ui {
+  class Widget;
+  class Window;
+
+  // Wraps a native window (os::Window). On each "display" we can show
+  // the main manager or a window (containedWidget), and a set of
+  // children window that doesn't have a native window counterpart
+  // (tooltips?)
+  class Display {
+  public:
+    Display(const os::WindowRef& nativeWindow,
+            Widget* containedWidget);
+
+    os::Window* nativeWindow() { return m_nativeWindow.get(); }
+    os::Surface* surface() const;
+
+    gfx::Size size() const;
+    gfx::Rect bounds() const { return gfx::Rect(size()); }
+
+    Widget* containedWidget() const { return m_containedWidget; }
+
+    // Mark the given rectangle as a area to be flipped to the real
+    // screen.
+    void dirtyRect(const gfx::Rect& bounds);
+
+    // Refreshes the real display with the UI content.
+    void flipDisplay();
+
+    // Returns the invalid region in the screen to being updated with
+    // PaintMessages. This region is cleared when each widget receives
+    // a paint message.
+    const gfx::Region& getInvalidRegion() const {
+      return m_invalidRegion;
+    }
+
+    void addInvalidRegion(const gfx::Region& b) {
+      m_invalidRegion |= b;
+    }
+
+    void subtractInvalidRegion(const gfx::Region& b) {
+      m_invalidRegion -= b;
+    }
+
+    void setInvalidRegion(const gfx::Region& b) {
+      m_invalidRegion = b;
+    }
+
+    void invalidateRect(const gfx::Rect& rect);
+    void invalidateRegion(const gfx::Region& region);
+
+    void addWindow(Window* window);
+    void removeWindow(Window* window);
+    void handleWindowZOrder(Window* window);
+    const std::vector<Window*>& getWindows() const { return m_windows; }
+
+  private:
+    os::WindowRef m_nativeWindow;
+    Widget* m_containedWidget;      // A ui::Manager or a ui::Window
+    std::vector<Window*> m_windows; // Sub-windows in this display
+    gfx::Region m_invalidRegion;    // Invalid region (we didn't receive paint messages yet for this).
+    gfx::Region m_dirtyRegion;      // Region to flip to the os::Display
+  };
+
+} // namespace ui
+
+#endif
diff --git a/src/ui/entry.cpp b/src/ui/entry.cpp
index 0a898a207..b78f2ec8e 100644
--- a/src/ui/entry.cpp
+++ b/src/ui/entry.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -16,7 +16,6 @@
 #include "os/draw_text.h"
 #include "os/font.h"
 #include "os/system.h"
-#include "ui/manager.h"
 #include "ui/menu.h"
 #include "ui/message.h"
 #include "ui/scale.h"
@@ -452,7 +451,7 @@ gfx::Size Entry::sizeHintWithText(Entry* entry,
     + 2*entry->theme()->getEntryCaretSize(entry).w
     + entry->border().width();
 
-  w = std::min(w, ui::display_w()/2);
+  w = std::min(w, ui::get_desktop_size().w/2);
 
   int h =
     + entry->font()->height()
@@ -471,7 +470,7 @@ void Entry::onSizeHint(SizeHintEvent& ev)
     + trailing
     + border().width();
 
-  w = std::min(w, ui::display_w()/2);
+  w = std::min(w, ui::get_desktop_size().w/2);
 
   int h =
     + font()->height()
diff --git a/src/ui/fit_bounds.cpp b/src/ui/fit_bounds.cpp
index 3614eeaa9..ec8f05922 100644
--- a/src/ui/fit_bounds.cpp
+++ b/src/ui/fit_bounds.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019  Igara Studio S.A.
+// Copyright (C) 2019-2020  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -9,14 +9,17 @@
 #include "config.h"
 #endif
 
+#include "ui/fit_bounds.h"
+
 #include "base/clamp.h"
 #include "gfx/rect.h"
 #include "ui/base.h"
+#include "ui/display.h"
 #include "ui/system.h"
 
 namespace ui {
 
-int fit_bounds(int arrowAlign, const gfx::Rect& target, gfx::Rect& bounds)
+int fit_bounds(Display* display, int arrowAlign, const gfx::Rect& target, gfx::Rect& bounds)
 {
   bounds.x = target.x;
   bounds.y = target.y;
@@ -58,8 +61,9 @@ int fit_bounds(int arrowAlign, const gfx::Rect& target, gfx::Rect& bounds)
         break;
     }
 
-    bounds.x = base::clamp(bounds.x, 0, ui::display_w()-bounds.w);
-    bounds.y = base::clamp(bounds.y, 0, ui::display_h()-bounds.h);
+    gfx::Size displaySize = display->size();
+    bounds.x = base::clamp(bounds.x, 0, displaySize.w-bounds.w);
+    bounds.y = base::clamp(bounds.y, 0, displaySize.h-bounds.h);
 
     if (target.intersects(bounds)) {
       switch (trycount) {
diff --git a/src/ui/fit_bounds.h b/src/ui/fit_bounds.h
index f18f3b18b..f6d1451f6 100644
--- a/src/ui/fit_bounds.h
+++ b/src/ui/fit_bounds.h
@@ -1,18 +1,21 @@
 // Aseprite UI Library
+// Copyright (C) 2019  Igara Studio S.A.
 // Copyright (C) 2016  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
 
-#ifndef UI_POINT_AT_H_INCLUDED
-#define UI_POINT_AT_H_INCLUDED
+#ifndef UI_FIT_BOUNDS_H_INCLUDED
+#define UI_FIT_BOUNDS_H_INCLUDED
 #pragma once
 
 #include "gfx/fwd.h"
 
 namespace ui {
 
-  int fit_bounds(int arrowAlign, const gfx::Rect& target, gfx::Rect& bounds);
+  class Display;
+
+  int fit_bounds(Display* display, int arrowAlign, const gfx::Rect& target, gfx::Rect& bounds);
 
 } // namespace ui
 
diff --git a/src/ui/graphics.cpp b/src/ui/graphics.cpp
index 44eb97de7..9ee21b8c4 100644
--- a/src/ui/graphics.cpp
+++ b/src/ui/graphics.cpp
@@ -24,7 +24,7 @@
 #include "os/surface.h"
 #include "os/system.h"
 #include "os/window.h"
-#include "ui/manager.h"
+#include "ui/display.h"
 #include "ui/scale.h"
 #include "ui/theme.h"
 
@@ -34,8 +34,9 @@
 
 namespace ui {
 
-Graphics::Graphics(const os::SurfaceRef& surface, int dx, int dy)
-  : m_surface(surface)
+Graphics::Graphics(Display* display, const os::SurfaceRef& surface, int dx, int dy)
+  : m_display(display)
+  , m_surface(surface)
   , m_dx(dx)
   , m_dy(dy)
 {
@@ -45,8 +46,8 @@ Graphics::~Graphics()
 {
   // If we were drawing in the screen surface, we mark these regions
   // as dirty for the final flip.
-  if (m_surface == os::instance()->defaultWindow()->surface())
-    Manager::getDefault()->dirtyRect(m_dirtyBounds);
+  if (m_display)
+    m_display->dirtyRect(m_dirtyBounds);
 }
 
 int Graphics::width() const
@@ -611,8 +612,8 @@ void Graphics::dirty(const gfx::Rect& bounds)
 //////////////////////////////////////////////////////////////////////
 // ScreenGraphics
 
-ScreenGraphics::ScreenGraphics()
-  : Graphics(AddRef(os::instance()->defaultWindow()->surface()), 0, 0)
+ScreenGraphics::ScreenGraphics(Display* display)
+  : Graphics(display, AddRef(display->surface()), 0, 0)
 {
   setFont(AddRef(get_theme()->getDefaultFont()));
 }
diff --git a/src/ui/graphics.h b/src/ui/graphics.h
index d0db15fb9..2a5589692 100644
--- a/src/ui/graphics.h
+++ b/src/ui/graphics.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -33,7 +33,9 @@ namespace os {
 }
 
 namespace ui {
-  using os::Paint;
+  using os::Paint;              // Define ui::Paint = os::Paint
+
+  class Display;
 
   // Class to render a widget in the screen.
   class Graphics {
@@ -44,7 +46,7 @@ namespace ui {
       Checked,
     };
 
-    Graphics(const os::SurfaceRef& surface, int dx, int dy);
+    Graphics(Display* display, const os::SurfaceRef& surface, int dx, int dy);
     ~Graphics();
 
     int width() const;
@@ -127,6 +129,7 @@ namespace ui {
     gfx::Size doUIStringAlgorithm(const std::string& str, gfx::Color fg, gfx::Color bg, const gfx::Rect& rc, int align, bool draw);
     void dirty(const gfx::Rect& bounds);
 
+    Display* m_display;
     os::SurfaceRef m_surface;
     int m_dx;
     int m_dy;
@@ -138,7 +141,7 @@ namespace ui {
   // Class to draw directly in the screen.
   class ScreenGraphics : public Graphics {
   public:
-    ScreenGraphics();
+    ScreenGraphics(Display* display);
     virtual ~ScreenGraphics();
   };
 
diff --git a/src/ui/int_entry.cpp b/src/ui/int_entry.cpp
index 5e88a0dc0..dba24c90a 100644
--- a/src/ui/int_entry.cpp
+++ b/src/ui/int_entry.cpp
@@ -183,10 +183,11 @@ void IntEntry::openPopup()
 
   Rect rc = bounds();
   gfx::Size sz = m_popupWindow->sizeHint();
+  gfx::Size displaySize = display()->size();
   rc.w = 128*guiscale();
-  if (rc.x+rc.w > ui::display_w())
+  if (rc.x+rc.w > displaySize.w)
     rc.x = rc.x-rc.w+bounds().w;
-  if (rc.y+rc.h+sz.h < ui::display_h())
+  if (rc.y+rc.h+sz.h < displaySize.h)
     rc.y += rc.h;
   else
     rc.y -= sz.h;
diff --git a/src/ui/manager.cpp b/src/ui/manager.cpp
index be97a457f..2059ab1a6 100644
--- a/src/ui/manager.cpp
+++ b/src/ui/manager.cpp
@@ -76,7 +76,6 @@ typedef std::list<Message*> Messages;
 typedef std::list<Filter*> Filters;
 
 Manager* Manager::m_defaultManager = nullptr;
-gfx::Region Manager::m_dirtyRegion;
 
 #ifdef DEBUG_UI_THREADS
 static base::thread::native_id_type manager_thread = 0;
@@ -160,13 +159,15 @@ bool Manager::widgetAssociatedToManager(Widget* widget)
                     widget) != mouse_widgets_list.end());
 }
 
-Manager::Manager()
+Manager::Manager(const os::WindowRef& nativeWindow)
   : Widget(kManagerWidget)
-  , m_window(nullptr)
-  , m_eventQueue(nullptr)
+  , m_display(nativeWindow, this)
+  , m_eventQueue(os::instance()->eventQueue())
   , m_lockedWindow(nullptr)
   , m_mouseButton(kButtonNone)
 {
+  nativeWindow->setUserData(&m_display);
+
 #ifdef DEBUG_UI_THREADS
   ASSERT(!manager_thread);
   manager_thread = base::this_thread::native_id();
@@ -183,14 +184,15 @@ Manager::Manager()
     capture_widget = nullptr;
   }
 
-  setBounds(gfx::Rect(0, 0, ui::display_w(), ui::display_h()));
+  setBounds(m_display.bounds());
   setVisible(true);
 
-  m_dirtyRegion = bounds();
-
   // Default manager is the first one (and is always visible).
   if (!m_defaultManager)
     m_defaultManager = this;
+
+  // TODO check if this is needed
+  onNewDisplayConfiguration(&m_display);
 }
 
 Manager::~Manager()
@@ -226,16 +228,12 @@ Manager::~Manager()
   }
 }
 
-void Manager::setNativeWindow(os::Window* window)
+Display* Manager::getDisplayFromNativeWindow(os::Window* window) const
 {
-  base::ScopedValue<bool> lock(
-    auto_window_adjustment, false,
-    auto_window_adjustment);
-
-  m_window = window;
-  m_eventQueue = os::instance()->eventQueue();
-
-  onNewDisplayConfiguration();
+  if (window)
+    return window->userData<Display>();
+  else
+    return nullptr;
 }
 
 void Manager::run()
@@ -253,11 +251,8 @@ void Manager::run()
     loop.pumpMessages();
 }
 
-void Manager::flipDisplay()
+void Manager::flipAllDisplays()
 {
-  if (!m_window)
-    return;
-
   OverlayManager* overlays = OverlayManager::instance();
 
   update_cursor_overlay();
@@ -265,15 +260,15 @@ void Manager::flipDisplay()
   // Draw overlays.
   overlays->drawOverlays();
 
-  // Invalidate the dirty region in the laf::os::Display (the real OS window).
-  m_dirtyRegion.createIntersection(
-    m_dirtyRegion,
-    gfx::Region(gfx::Rect(0, 0, ui::display_w(), ui::display_h())));
+  m_display.flipDisplay();
+}
 
-  if (!m_dirtyRegion.isEmpty()) {
-    m_window->invalidateRegion(m_dirtyRegion);
-    m_dirtyRegion.clear();
-  }
+void Manager::updateAllDisplaysWithNewScale(int scale)
+{
+  os::Window* nativeWindow = m_display.nativeWindow();
+  nativeWindow->setScale(scale);
+
+  onNewDisplayConfiguration(&m_display);
 }
 
 bool Manager::generateMessages()
@@ -308,7 +303,8 @@ bool Manager::generateMessages()
     return false;
 }
 
-void Manager::generateSetCursorMessage(const gfx::Point& mousePos,
+void Manager::generateSetCursorMessage(Display* display,
+                                       const gfx::Point& mousePos,
                                        KeyModifiers modifiers,
                                        PointerType pointerType)
 {
@@ -319,7 +315,8 @@ void Manager::generateSetCursorMessage(const gfx::Point& mousePos,
   if (dst)
     enqueueMessage(
       newMouseMessage(
-        kSetCursorMessage, dst,
+        kSetCursorMessage,
+        display, dst,
         mousePos,
         pointerType,
         m_mouseButton,
@@ -375,10 +372,15 @@ void Manager::generateMessagesFromOSEvents()
     if (osEvent.type() == os::Event::None)
       break;
 
+    Display* display = getDisplayFromNativeWindow(osEvent.window().get());
+    if (!display)
+      display = this->display();
+
     switch (osEvent.type()) {
 
       case os::Event::CloseApp: {
         Message* msg = new Message(kCloseDisplayMessage);
+        msg->setDisplay(display);
         msg->setRecipient(this);
         msg->setPropagateToChildren(true);
         enqueueMessage(msg);
@@ -387,6 +389,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::CloseWindow: {
         Message* msg = new Message(kCloseDisplayMessage);
+        msg->setDisplay(display);
         msg->setRecipient(this);
         msg->setPropagateToChildren(true);
         enqueueMessage(msg);
@@ -395,6 +398,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::ResizeWindow: {
         Message* msg = new Message(kResizeDisplayMessage);
+        msg->setDisplay(display);
         msg->setRecipient(this);
         msg->setPropagateToChildren(true);
         enqueueMessage(msg);
@@ -403,6 +407,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::DropFiles: {
         Message* msg = new DropFilesMessage(osEvent.files());
+        msg->setDisplay(display);
         msg->setRecipient(this);
         enqueueMessage(msg);
         break;
@@ -419,6 +424,8 @@ void Manager::generateMessagesFromOSEvents()
           osEvent.unicodeChar(),
           osEvent.repeat());
 
+        msg->setDisplay(display);
+
         if (osEvent.isDeadKey())
           static_cast<KeyMessage*>(msg)->setDeadKey(true);
 
@@ -449,6 +456,7 @@ void Manager::generateMessagesFromOSEvents()
       case os::Event::MouseMove: {
         _internal_set_mouse_position(osEvent.position());
         handleMouseMove(
+          display,
           osEvent.position(),
           osEvent.modifiers(),
           osEvent.pointerType(),
@@ -459,6 +467,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::MouseDown: {
         handleMouseDown(
+          display,
           osEvent.position(),
           m_mouseButton = mouse_button_from_os_to_ui(osEvent),
           osEvent.modifiers(),
@@ -468,6 +477,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::MouseUp: {
         handleMouseUp(
+          display,
           osEvent.position(),
           mouse_button_from_os_to_ui(osEvent),
           osEvent.modifiers(),
@@ -478,6 +488,7 @@ void Manager::generateMessagesFromOSEvents()
 
       case os::Event::MouseDoubleClick: {
         handleMouseDoubleClick(
+          display,
           osEvent.position(),
           m_mouseButton = mouse_button_from_os_to_ui(osEvent),
           osEvent.modifiers(),
@@ -486,7 +497,8 @@ void Manager::generateMessagesFromOSEvents()
       }
 
       case os::Event::MouseWheel: {
-        handleMouseWheel(osEvent.position(),
+        handleMouseWheel(display,
+                         osEvent.position(),
                          osEvent.modifiers(),
                          osEvent.pointerType(),
                          osEvent.wheelDelta(),
@@ -497,7 +509,8 @@ void Manager::generateMessagesFromOSEvents()
       case os::Event::TouchMagnify: {
         _internal_set_mouse_position(osEvent.position());
 
-        handleTouchMagnify(osEvent.position(),
+        handleTouchMagnify(display,
+                           osEvent.position(),
                            osEvent.modifiers(),
                            osEvent.magnification());
         break;
@@ -515,13 +528,20 @@ void Manager::generateMessagesFromOSEvents()
   // Generate just one kSetCursorMessage for the last mouse position
   if (lastMouseMoveEvent.type() != os::Event::None) {
     osEvent = lastMouseMoveEvent;
-    generateSetCursorMessage(osEvent.position(),
+
+    Display* display = getDisplayFromNativeWindow(osEvent.window().get());
+    if (!display)
+      display = this->display();
+
+    generateSetCursorMessage(display,
+                             osEvent.position(),
                              osEvent.modifiers(),
                              osEvent.pointerType());
   }
 }
 
-void Manager::handleMouseMove(const gfx::Point& mousePos,
+void Manager::handleMouseMove(Display* display,
+                              const gfx::Point& mousePos,
                               const KeyModifiers modifiers,
                               const PointerType pointerType,
                               const float pressure)
@@ -532,7 +552,8 @@ void Manager::handleMouseMove(const gfx::Point& mousePos,
   Widget* dst = (capture_widget ? capture_widget: mouse_widget);
   enqueueMessage(
     newMouseMessage(
-      kMouseMoveMessage, dst,
+      kMouseMoveMessage,
+      display, dst,
       mousePos,
       pointerType,
       m_mouseButton,
@@ -542,7 +563,8 @@ void Manager::handleMouseMove(const gfx::Point& mousePos,
       pressure));
 }
 
-void Manager::handleMouseDown(const gfx::Point& mousePos,
+void Manager::handleMouseDown(Display* display,
+                              const gfx::Point& mousePos,
                               MouseButton mouseButton,
                               KeyModifiers modifiers,
                               PointerType pointerType)
@@ -552,6 +574,7 @@ void Manager::handleMouseDown(const gfx::Point& mousePos,
   enqueueMessage(
     newMouseMessage(
       kMouseDownMessage,
+      display,
       (capture_widget ? capture_widget: mouse_widget),
       mousePos,
       pointerType,
@@ -559,7 +582,8 @@ void Manager::handleMouseDown(const gfx::Point& mousePos,
       modifiers));
 }
 
-void Manager::handleMouseUp(const gfx::Point& mousePos,
+void Manager::handleMouseUp(Display* display,
+                            const gfx::Point& mousePos,
                             MouseButton mouseButton,
                             KeyModifiers modifiers,
                             PointerType pointerType)
@@ -567,6 +591,7 @@ void Manager::handleMouseUp(const gfx::Point& mousePos,
   enqueueMessage(
     newMouseMessage(
       kMouseUpMessage,
+      display,
       (capture_widget ? capture_widget: mouse_widget),
       mousePos,
       pointerType,
@@ -574,7 +599,8 @@ void Manager::handleMouseUp(const gfx::Point& mousePos,
       modifiers));
 }
 
-void Manager::handleMouseDoubleClick(const gfx::Point& mousePos,
+void Manager::handleMouseDoubleClick(Display* display,
+                                     const gfx::Point& mousePos,
                                      MouseButton mouseButton,
                                      KeyModifiers modifiers,
                                      PointerType pointerType)
@@ -584,12 +610,13 @@ void Manager::handleMouseDoubleClick(const gfx::Point& mousePos,
     enqueueMessage(
       newMouseMessage(
         kDoubleClickMessage,
-        dst, mousePos, pointerType,
+        display, dst, mousePos, pointerType,
         mouseButton, modifiers));
   }
 }
 
-void Manager::handleMouseWheel(const gfx::Point& mousePos,
+void Manager::handleMouseWheel(Display* display,
+                               const gfx::Point& mousePos,
                                KeyModifiers modifiers,
                                PointerType pointerType,
                                const gfx::Point& wheelDelta,
@@ -597,12 +624,14 @@ void Manager::handleMouseWheel(const gfx::Point& mousePos,
 {
   enqueueMessage(newMouseMessage(
       kMouseWheelMessage,
+      display,
       (capture_widget ? capture_widget: mouse_widget),
       mousePos, pointerType, m_mouseButton, modifiers,
       wheelDelta, preciseWheel));
 }
 
-void Manager::handleTouchMagnify(const gfx::Point& mousePos,
+void Manager::handleTouchMagnify(Display* display,
+                                 const gfx::Point& mousePos,
                                  const KeyModifiers modifiers,
                                  const double magnification)
 {
@@ -614,6 +643,7 @@ void Manager::handleTouchMagnify(const gfx::Point& mousePos,
       mousePos,
       magnification);
 
+    msg->setDisplay(display);
     msg->setRecipient(widget);
 
     enqueueMessage(msg);
@@ -622,6 +652,8 @@ void Manager::handleTouchMagnify(const gfx::Point& mousePos,
 
 // Handles Z order: Send the window to top (only when you click in a
 // window that aren't the desktop).
+//
+// TODO code similar to Display::handleWindowZOrder()
 void Manager::handleWindowZOrder()
 {
   if (capture_widget || !mouse_widget)
@@ -642,6 +674,8 @@ void Manager::handleWindowZOrder()
     (window != win_manager->getTopWindow())) {
     base::ScopedValue<Widget*> scoped(m_lockedWindow, window, nullptr);
 
+    window->display()->handleWindowZOrder(window);
+
     // Put it in the top of the list
     win_manager->removeChild(window);
 
@@ -718,8 +752,8 @@ void Manager::dispatchMessages()
       flushRedraw();
       pumpQueue();
 
-      // Flip the back-buffer to the real display.
-      flipDisplay();
+      // Flip back-buffers to real displays.
+      flipAllDisplays();
     }
   }
 }
@@ -854,8 +888,11 @@ void Manager::setMouse(Widget* widget)
     // Put the mouse
     mouse_widget = widget;
     if (widget) {
+      Display* display = mouse_widget->display();
+
       auto msg = newMouseMessage(
-        kMouseEnterMessage, nullptr,
+        kMouseEnterMessage,
+        display, nullptr,
         get_mouse_position(),
         PointerType::Unknown,
         m_mouseButton,
@@ -865,7 +902,8 @@ void Manager::setMouse(Widget* widget)
       msg->setPropagateToParent(true);
       msg->setCommonAncestor(commonAncestor);
       enqueueMessage(msg);
-      generateSetCursorMessage(get_mouse_position(),
+      generateSetCursorMessage(display,
+                               get_mouse_position(),
                                kKeyUninitializedModifier,
                                PointerType::Unknown);
 
@@ -888,7 +926,10 @@ void Manager::setCapture(Widget* widget)
   widget->enableFlags(HAS_CAPTURE);
   capture_widget = widget;
 
-  m_window->captureMouse();
+  Display* display = (widget ? widget->display(): &m_display);
+  ASSERT(display && display->nativeWindow());
+  if (display && display->nativeWindow())
+    display->nativeWindow()->captureMouse();
 }
 
 // Sets the focus to the "magnetic" widget inside the window
@@ -925,10 +966,14 @@ void Manager::freeMouse()
 void Manager::freeCapture()
 {
   if (capture_widget) {
+    Display* display = capture_widget->display();
+
     capture_widget->disableFlags(HAS_CAPTURE);
     capture_widget = nullptr;
 
-    m_window->releaseMouse();
+    ASSERT(display && display->nativeWindow());
+    if (display && display->nativeWindow())
+      display->nativeWindow()->releaseMouse();
   }
 }
 
@@ -1073,11 +1118,6 @@ bool Manager::isFocusMovementMessage(Message* msg)
   return false;
 }
 
-void Manager::dirtyRect(const gfx::Rect& bounds)
-{
-  m_dirtyRegion.createUnion(m_dirtyRegion, gfx::Region(bounds));
-}
-
 // Configures the window for begin the loop
 void Manager::_openWindow(Window* window)
 {
@@ -1100,6 +1140,9 @@ void Manager::_openWindow(Window* window)
   // Relayout
   window->layout();
 
+  // Same display as the manager.
+  window->setDisplay(this->display());
+
   // Dirty the entire window and show it
   window->setVisible(true);
   window->invalidate();
@@ -1121,6 +1164,8 @@ void Manager::_openWindow(Window* window)
 
 void Manager::_closeWindow(Window* window, bool redraw_background)
 {
+  window->setDisplay(nullptr);
+
   if (!hasChild(window))
     return;
 
@@ -1189,7 +1234,7 @@ bool Manager::onProcessMessage(Message* msg)
       return true;
 
     case kResizeDisplayMessage:
-      onNewDisplayConfiguration();
+      onNewDisplayConfiguration(msg->display());
       break;
 
     case kKeyDownMessage:
@@ -1236,7 +1281,7 @@ void Manager::onResize(ResizeEvent& ev)
   setBoundsQuietly(new_pos);
 
   // The whole manager area is invalid now.
-  m_invalidRegion = gfx::Region(new_pos);
+  m_display.setInvalidRegion(gfx::Region(new_pos));
 
   const int dx = new_pos.x - old_pos.x;
   const int dy = new_pos.y - old_pos.y;
@@ -1306,11 +1351,12 @@ void Manager::onInitTheme(InitThemeEvent& ev)
         window->layout();
       }
       else {
+        gfx::Size displaySize = m_display.size();
         gfx::Rect bounds = window->bounds();
         bounds *= newUIScale;
         bounds /= oldUIScale;
-        bounds.x = base::clamp(bounds.x, 0, m_window->width() - bounds.w);
-        bounds.y = base::clamp(bounds.y, 0, m_window->height() - bounds.h);
+        bounds.x = base::clamp(bounds.x, 0, displaySize.w - bounds.w);
+        bounds.y = base::clamp(bounds.y, 0, displaySize.h - bounds.h);
         window->setBounds(bounds);
       }
     }
@@ -1322,19 +1368,19 @@ LayoutIO* Manager::onGetLayoutIO()
   return nullptr;
 }
 
-void Manager::onNewDisplayConfiguration()
+void Manager::onNewDisplayConfiguration(Display* display)
 {
-  if (m_window) {
-    int w = m_window->width() / m_window->scale();
-    int h = m_window->height() / m_window->scale();
-    if ((bounds().w != w ||
-         bounds().h != h)) {
-      setBounds(gfx::Rect(0, 0, w, h));
-    }
+  ASSERT(display);
+  Widget* container = display->containedWidget();
+
+  gfx::Size displaySize = display->size();
+  if ((bounds().w != displaySize.w ||
+       bounds().h != displaySize.h)) {
+    container->setBounds(gfx::Rect(displaySize));
   }
 
-  _internal_set_mouse_window(m_window);
-  invalidate();
+  _internal_set_mouse_display(display);
+  container->invalidate();
   flushRedraw();
 }
 
@@ -1497,10 +1543,11 @@ bool Manager::sendMessageToWidget(Message* msg, Widget* widget)
 
     PaintMessage* paintMsg = static_cast<PaintMessage*>(msg);
 
+    // TODO use paintMsg->display() here
     // Restore overlays in the region that we're going to paint.
     OverlayManager::instance()->restoreOverlappedAreas(paintMsg->rect());
 
-    os::Surface* surface = m_window->surface();
+    os::Surface* surface = paintMsg->display()->surface();
     surface->saveClip();
 
     if (surface->clipRect(paintMsg->rect())) {
@@ -1520,8 +1567,7 @@ bool Manager::sendMessageToWidget(Message* msg, Widget* widget)
       }
 
       if (m_window) {
-        m_window->invalidateRegion(
-          gfx::Region(gfx::Rect(0, 0, display_w(), display_h())));
+        m_window->invalidateRegion(gfx::Region(m_window->bounds()));
         // TODO m_window->update() ??
       }
 
@@ -1539,7 +1585,7 @@ bool Manager::sendMessageToWidget(Message* msg, Widget* widget)
 
     // As this kPaintMessage's rectangle was updated, we can
     // remove it from "m_invalidRegion".
-    m_invalidRegion -= gfx::Region(paintMsg->rect());
+    paintMsg->display()->subtractInvalidRegion(gfx::Region(paintMsg->rect()));
   }
   else {
     // Call the message handler
@@ -1690,6 +1736,7 @@ Widget* Manager::findMagneticWidget(Widget* widget)
 // static
 Message* Manager::newMouseMessage(
   MessageType type,
+  Display* display,
   Widget* widget,
   const gfx::Point& mousePos,
   PointerType pointerType,
@@ -1716,6 +1763,9 @@ Message* Manager::newMouseMessage(
     type, pointerType, button, modifiers, mousePos,
     wheelDelta, preciseWheel, pressure);
 
+  if (display)
+    msg->setDisplay(display);
+
   if (widget)
     msg->setRecipient(widget);
 
diff --git a/src/ui/manager.h b/src/ui/manager.h
index 8e8ecf520..9a5fea4be 100644
--- a/src/ui/manager.h
+++ b/src/ui/manager.h
@@ -10,6 +10,7 @@
 #pragma once
 
 #include "gfx/region.h"
+#include "ui/display.h"
 #include "ui/keys.h"
 #include "ui/message_type.h"
 #include "ui/mouse_button.h"
@@ -32,17 +33,19 @@ namespace ui {
     static Manager* getDefault() { return m_defaultManager; }
     static bool widgetAssociatedToManager(Widget* widget);
 
-    Manager();
+    Manager(const os::WindowRef& nativeWindow);
     ~Manager();
 
-    os::Window* nativeWindow() { return m_window; }
-    void setNativeWindow(os::Window* window);
+    Display* display() { return &m_display; }
+    Display* getDisplayFromNativeWindow(os::Window* window) const;
 
     // Executes the main message loop.
     void run();
 
-    // Refreshes the real display with the UI content.
-    void flipDisplay();
+    // Refreshes all real displays with the UI content.
+    void flipAllDisplays();
+
+    void updateAllDisplaysWithNewScale(int scale);
 
     // Adds the given "msg" message to the queue of messages to be
     // dispached. "msg" cannot be used after this function, it'll be
@@ -86,21 +89,6 @@ namespace ui {
     bool isFocusMovementMessage(Message* msg);
     bool processFocusMovementMessage(Message* msg);
 
-    // Returns the invalid region in the screen to being updated with
-    // PaintMessages. This region is cleared when each widget receives
-    // a paint message.
-    const gfx::Region& getInvalidRegion() const {
-      return m_invalidRegion;
-    }
-
-    void addInvalidRegion(const gfx::Region& b) {
-      m_invalidRegion |= b;
-    }
-
-    // Mark the given rectangle as a area to be flipped to the real
-    // screen
-    void dirtyRect(const gfx::Rect& bounds);
-
     void _openWindow(Window* window);
     void _closeWindow(Window* window, bool redraw_background);
 
@@ -112,35 +100,43 @@ namespace ui {
     void onBroadcastMouseMessage(WidgetsList& targets) override;
     void onInitTheme(InitThemeEvent& ev) override;
     virtual LayoutIO* onGetLayoutIO();
-    virtual void onNewDisplayConfiguration();
+    virtual void onNewDisplayConfiguration(Display* display);
 
   private:
-    void generateSetCursorMessage(const gfx::Point& mousePos,
+    void generateSetCursorMessage(Display* display,
+                                  const gfx::Point& mousePos,
                                   KeyModifiers modifiers,
                                   PointerType pointerType);
     void generateMessagesFromOSEvents();
-    void handleMouseMove(const gfx::Point& mousePos,
+
+    void handleMouseMove(Display* display,
+                         const gfx::Point& mousePos,
                          const KeyModifiers modifiers,
                          const PointerType pointerType,
                          const float pressure);
-    void handleMouseDown(const gfx::Point& mousePos,
+    void handleMouseDown(Display* display,
+                         const gfx::Point& mousePos,
                          MouseButton mouseButton,
                          KeyModifiers modifiers,
                          PointerType pointerType);
-    void handleMouseUp(const gfx::Point& mousePos,
+    void handleMouseUp(Display* display,
+                       const gfx::Point& mousePos,
                        MouseButton mouseButton,
                        KeyModifiers modifiers,
                        PointerType pointerType);
-    void handleMouseDoubleClick(const gfx::Point& mousePos,
+    void handleMouseDoubleClick(Display* display,
+                                const gfx::Point& mousePos,
                                 MouseButton mouseButton,
                                 KeyModifiers modifiers,
                                 PointerType pointerType);
-    void handleMouseWheel(const gfx::Point& mousePos,
+    void handleMouseWheel(Display* display,
+                          const gfx::Point& mousePos,
                           KeyModifiers modifiers,
                           PointerType pointerType,
                           const gfx::Point& wheelDelta,
                           bool preciseWheel);
-    void handleTouchMagnify(const gfx::Point& mousePos,
+    void handleTouchMagnify(Display* display,
+                            const gfx::Point& mousePos,
                             const KeyModifiers modifiers,
                             const double magnification);
     void handleWindowZOrder();
@@ -154,7 +150,9 @@ namespace ui {
     static Widget* findMagneticWidget(Widget* widget);
     static Message* newMouseMessage(
       MessageType type,
-      Widget* widget, const gfx::Point& mousePos,
+      Display* display,
+      Widget* widget,
+      const gfx::Point& mousePos,
       PointerType pointerType,
       MouseButton button,
       KeyModifiers modifiers,
@@ -164,12 +162,10 @@ namespace ui {
     void broadcastKeyMsg(Message* msg);
 
     static Manager* m_defaultManager;
-    static gfx::Region m_dirtyRegion;
 
     WidgetsList m_garbage;
-    os::Window* m_window;
+    Display m_display;
     os::EventQueue* m_eventQueue;
-    gfx::Region m_invalidRegion;  // Invalid region (we didn't receive paint messages yet for this).
 
     // This member is used to make freeWidget() a no-op when we
     // restack a window if the user clicks on it.
diff --git a/src/ui/menu.cpp b/src/ui/menu.cpp
index d533a0f7e..7a3b4338e 100644
--- a/src/ui/menu.cpp
+++ b/src/ui/menu.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -14,6 +14,7 @@
 #include "base/clamp.h"
 #include "gfx/size.h"
 #include "os/font.h"
+#include "ui/display.h"
 #include "ui/intern.h"
 #include "ui/ui.h"
 
@@ -102,14 +103,15 @@ static MenuItem* find_previtem(Menu* menu, MenuItem* menuitem);
 static void add_scrollbars_if_needed(Window* window)
 {
   const gfx::Rect rc0 = window->bounds();
+  gfx::Size displaySize = window->display()->size();
   gfx::Rect rc = rc0;
 
   if (rc.x < 0) {
     rc.w += rc.x;
     rc.x = 0;
   }
-  if (rc.x2() > ui::display_w()) {
-    rc.w = ui::display_w() - rc.x;
+  if (rc.x2() > displaySize.w) {
+    rc.w = displaySize.w - rc.x;
   }
 
   bool vscrollbarsAdded = false;
@@ -118,8 +120,8 @@ static void add_scrollbars_if_needed(Window* window)
     rc.y = 0;
     vscrollbarsAdded = true;
   }
-  if (rc.y2() > ui::display_h()) {
-    rc.h = ui::display_h() - rc.y;
+  if (rc.y2() > displaySize.h) {
+    rc.h = displaySize.h - rc.y;
     vscrollbarsAdded = true;
   }
 
@@ -133,11 +135,11 @@ static void add_scrollbars_if_needed(Window* window)
 
   if (vscrollbarsAdded) {
     rc.w += 2*view->verticalBar()->getBarWidth();
-    if (rc.x2() > ui::display_w()) {
-      rc.x = ui::display_w() - rc.w;
+    if (rc.x2() > displaySize.w) {
+      rc.x = displaySize.w - rc.w;
       if (rc.x < 0) {
         rc.x = 0;
-        rc.w = ui::display_w();
+        rc.w = displaySize.w;
       }
     }
   }
@@ -311,6 +313,7 @@ void Menu::showPopup(const gfx::Point& pos)
   MenuBaseData* base = menubox->createBase();
   base->was_clicked = true;
   window->setMoveable(false);   // Can't move the window
+  window->setSizeable(false);   // Can't resize the window
 
   // Set children
   menubox->setMenu(this);
@@ -320,9 +323,10 @@ void Menu::showPopup(const gfx::Point& pos)
   window->remapWindow();
 
   // Menubox position
+  gfx::Size displaySize = display()->size();
   window->positionWindow(
-    base::clamp(pos.x, 0, ui::display_w() - window->bounds().w),
-    base::clamp(pos.y, 0, ui::display_h() - window->bounds().h));
+    base::clamp(pos.x, 0, displaySize.w - window->bounds().w),
+    base::clamp(pos.y, 0, displaySize.h - window->bounds().h));
 
   add_scrollbars_if_needed(window.get());
 
@@ -821,9 +825,10 @@ bool MenuItem::onProcessMessage(Message* msg)
 
         // Menubox position
         Rect pos = window->bounds();
+        Size displaySize = display()->size();
 
         if (inBar()) {
-          pos.x = base::clamp(bounds().x, 0, ui::display_w()-pos.w);
+          pos.x = base::clamp(bounds().x, 0, displaySize.w-pos.w);
           pos.y = std::max(0, bounds().y2());
         }
         else {
@@ -832,9 +837,9 @@ bool MenuItem::onProcessMessage(Message* msg)
           int x, y = bounds().y-3*guiscale();
           Rect r1(0, 0, pos.w, pos.h), r2(0, 0, pos.w, pos.h);
 
-          r1.x = x_left = base::clamp(x_left, 0, ui::display_w()-pos.w);
-          r2.x = x_right = base::clamp(x_right, 0, ui::display_w()-pos.w);
-          r1.y = r2.y = y = base::clamp(y, 0, ui::display_h()-pos.h);
+          r1.x = x_left = base::clamp(x_left, 0, displaySize.w-pos.w);
+          r2.x = x_right = base::clamp(x_right, 0, displaySize.w-pos.w);
+          r1.y = r2.y = y = base::clamp(y, 0, displaySize.h-pos.h);
 
           // Calculate both intersections
           gfx::Rect s1 = r1.createIntersection(old_pos);
@@ -1408,6 +1413,7 @@ MenuBoxWindow::MenuBoxWindow(MenuBox* menubox)
   : Window(WithoutTitleBar, "")
 {
   setMoveable(false); // Can't move the window
+  setSizeable(false); // Can't resize the window
   addChild(menubox);
   remapWindow();
 }
diff --git a/src/ui/message.cpp b/src/ui/message.cpp
index 504e21f27..71f326dc6 100644
--- a/src/ui/message.cpp
+++ b/src/ui/message.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,7 +13,6 @@
 
 #include "base/memory.h"
 #include "os/system.h"
-#include "ui/manager.h"
 #include "ui/widget.h"
 
 #include <cstring>
@@ -23,6 +22,7 @@ namespace ui {
 Message::Message(MessageType type, KeyModifiers modifiers)
   : m_type(type)
   , m_flags(0)
+  , m_display(nullptr)
   , m_recipient(nullptr)
   , m_commonAncestor(nullptr)
 {
@@ -36,6 +36,11 @@ Message::~Message()
 {
 }
 
+void Message::setDisplay(Display* display)
+{
+  m_display = display;
+}
+
 void Message::setRecipient(Widget* widget)
 {
   ASSERT(m_recipient == nullptr);
diff --git a/src/ui/message.h b/src/ui/message.h
index b8787360d..3c01a66df 100644
--- a/src/ui/message.h
+++ b/src/ui/message.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -20,6 +20,7 @@
 
 namespace ui {
 
+  class Display;
   class Timer;
   class Widget;
 
@@ -35,6 +36,7 @@ namespace ui {
     virtual ~Message();
 
     MessageType type() const { return m_type; }
+    Display* display() const { return m_display; }
     Widget* recipient() const { return m_recipient; }
     bool fromFilter() const { return hasFlag(FromFilter); }
     void setFromFilter(const bool state) { setFlag(FromFilter, state); }
@@ -50,6 +52,7 @@ namespace ui {
     bool onlyCmdPressed() const { return m_modifiers == kKeyCmdModifier; }
     bool onlyWinPressed() const { return m_modifiers == kKeyWinModifier; }
 
+    void setDisplay(Display* display);
     void setRecipient(Widget* widget);
     void removeRecipient(Widget* widget);
 
@@ -72,6 +75,7 @@ namespace ui {
 
     MessageType m_type;       // Type of message
     int m_flags;              // Special flags for this message
+    Display* m_display;
     Widget* m_recipient;      // Recipient of this message
     Widget* m_commonAncestor; // Common ancestor between the Leave <-> Enter messages
     KeyModifiers m_modifiers; // Key modifiers pressed when message was created
@@ -101,7 +105,9 @@ namespace ui {
   class PaintMessage : public Message {
   public:
     PaintMessage(int count, const gfx::Rect& rect)
-      : Message(kPaintMessage), m_count(count), m_rect(rect) {
+      : Message(kPaintMessage)
+      , m_count(count)
+      , m_rect(rect) {
     }
 
     int count() const { return m_count; }
diff --git a/src/ui/move_region.cpp b/src/ui/move_region.cpp
index bd5b65a0e..8afefcb0d 100644
--- a/src/ui/move_region.cpp
+++ b/src/ui/move_region.cpp
@@ -22,9 +22,13 @@ namespace ui {
 
 using namespace gfx;
 
-void move_region(Manager* manager, const Region& region, int dx, int dy)
+void move_region(Display* display, const Region& region, int dx, int dy)
 {
-  os::Window* window = manager->nativeWindow();
+  ASSERT(display);
+  if (!display)
+    return;
+
+  os::Window* window = display->nativeWindow();
   ASSERT(window);
   if (!window)
     return;
@@ -43,7 +47,7 @@ void move_region(Manager* manager, const Region& region, int dx, int dy)
     surface->scrollTo(rc, dx, dy);
 
     rc.offset(dx, dy);
-    manager->dirtyRect(rc);
+    display->dirtyRect(rc);
   }
   // As rectangles in the region internals are separated by bands
   // through the y-axis, we can sort the rectangles by y-axis and then
@@ -87,7 +91,7 @@ void move_region(Manager* manager, const Region& region, int dx, int dy)
       surface->scrollTo(rc, dx, dy);
 
       rc.offset(dx, dy);
-      manager->dirtyRect(rc);
+      display->dirtyRect(rc);
     }
   }
 
diff --git a/src/ui/move_region.h b/src/ui/move_region.h
index e945fc231..74b3b5d7f 100644
--- a/src/ui/move_region.h
+++ b/src/ui/move_region.h
@@ -1,4 +1,5 @@
 // Aseprite UI Library
+// Copyright (C) 2019  Igara Studio S.A.
 // Copyright (C) 2001-2015  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -12,9 +13,9 @@
 
 namespace ui {
 
-  class Manager;
+  class Display;
 
-  void move_region(Manager* manager, const gfx::Region& region, int dx, int dy);
+  void move_region(Display* display, const gfx::Region& region, int dx, int dy);
 
 } // namespace ui
 
diff --git a/src/ui/overlay.cpp b/src/ui/overlay.cpp
index 18be98fb4..d28266524 100644
--- a/src/ui/overlay.cpp
+++ b/src/ui/overlay.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,14 +13,16 @@
 
 #include "os/surface.h"
 #include "os/system.h"
-#include "ui/manager.h"
+#include "ui/display.h"
 
 namespace ui {
 
-Overlay::Overlay(const os::SurfaceRef& overlaySurface,
+Overlay::Overlay(Display* display,
+                 const os::SurfaceRef& overlaySurface,
                  const gfx::Point& pos,
                  ZOrder zorder)
-  : m_surface(overlaySurface)
+  : m_display(display)
+  , m_surface(overlaySurface)
   , m_overlap(nullptr)
   , m_captured(nullptr)
   , m_pos(pos)
@@ -33,11 +35,8 @@ Overlay::~Overlay()
   ASSERT(!m_captured);
 
   if (m_surface) {
-    Manager* manager = Manager::getDefault();
-    if (manager)
-      manager->invalidateRect(gfx::Rect(m_pos.x, m_pos.y,
-                                        m_surface->width(),
-                                        m_surface->height()));
+    if (m_display)
+      m_display->invalidateRect(bounds());
     m_surface.reset();
   }
 
@@ -69,7 +68,7 @@ void Overlay::drawOverlay()
   os::SurfaceLock lock(m_surface.get());
   m_captured->drawRgbaSurface(m_surface.get(), m_pos.x, m_pos.y);
 
-  Manager::getDefault()->dirtyRect(
+  m_display->dirtyRect(
     gfx::Rect(m_pos.x, m_pos.y,
               m_surface->width(),
               m_surface->height()));
@@ -83,24 +82,27 @@ void Overlay::moveOverlay(const gfx::Point& newPos)
   m_pos = newPos;
 }
 
-void Overlay::captureOverlappedArea(os::Surface* screen)
+void Overlay::captureOverlappedArea()
 {
   if (!m_surface ||
       m_captured)
     return;
 
+  os::Surface* displaySurface = m_display->surface();
+  os::SurfaceLock lockDisplaySurface(displaySurface);
+
   if (!m_overlap) {
     // Use the same color space for the overlay as in the screen
     m_overlap = os::instance()->makeSurface(m_surface->width(),
                                             m_surface->height(),
-                                            screen->colorSpace());
+                                            displaySurface->colorSpace());
   }
 
   os::SurfaceLock lock(m_overlap.get());
-  screen->blitTo(m_overlap.get(), m_pos.x, m_pos.y, 0, 0,
-                 m_overlap->width(), m_overlap->height());
+  displaySurface->blitTo(m_overlap.get(), m_pos.x, m_pos.y, 0, 0,
+                         m_overlap->width(), m_overlap->height());
 
-  m_captured = screen;
+  m_captured = displaySurface;
 }
 
 void Overlay::restoreOverlappedArea(const gfx::Rect& restoreBounds)
@@ -118,8 +120,7 @@ void Overlay::restoreOverlappedArea(const gfx::Rect& restoreBounds)
   m_overlap->blitTo(m_captured, 0, 0, m_pos.x, m_pos.y,
                     m_overlap->width(), m_overlap->height());
 
-  Manager::getDefault()->dirtyRect(bounds());
-
+  m_display->dirtyRect(bounds());
   m_captured = nullptr;
 }
 
diff --git a/src/ui/overlay.h b/src/ui/overlay.h
index 79ed040eb..057305267 100644
--- a/src/ui/overlay.h
+++ b/src/ui/overlay.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -20,6 +20,7 @@ namespace os {
 }
 
 namespace ui {
+  class Display;
 
   class Overlay;
   using OverlayRef = base::Ref<Overlay>;
@@ -31,7 +32,8 @@ namespace ui {
       MouseZOrder = 5000
     };
 
-    Overlay(const os::SurfaceRef& overlaySurface,
+    Overlay(Display* display,
+            const os::SurfaceRef& overlaySurface,
             const gfx::Point& pos,
             ZOrder zorder = NormalZOrder);
     ~Overlay();
@@ -41,7 +43,7 @@ namespace ui {
     const gfx::Point& position() const { return m_pos; }
     gfx::Rect bounds() const;
 
-    void captureOverlappedArea(os::Surface* screen);
+    void captureOverlappedArea();
     void restoreOverlappedArea(const gfx::Rect& restoreBounds);
 
     void drawOverlay();
@@ -52,6 +54,7 @@ namespace ui {
     }
 
   private:
+    Display* m_display;
     os::SurfaceRef m_surface;
     os::SurfaceRef m_overlap;
 
diff --git a/src/ui/overlay_manager.cpp b/src/ui/overlay_manager.cpp
index 5bf0fd4bf..e2b1cf69f 100644
--- a/src/ui/overlay_manager.cpp
+++ b/src/ui/overlay_manager.cpp
@@ -11,8 +11,6 @@
 
 #include "ui/overlay_manager.h"
 
-#include "os/surface.h"
-#include "os/window.h"
 #include "ui/manager.h"
 #include "ui/overlay.h"
 
@@ -68,11 +66,6 @@ void OverlayManager::restoreOverlappedAreas(const gfx::Rect& restoreBounds)
   if (m_overlays.empty())
     return;
 
-  // TODO can we remove this?
-  Manager* manager = Manager::getDefault();
-  if (!manager)
-    return;
-
   for (auto& overlay : *this)
     overlay->restoreOverlappedArea(restoreBounds);
 }
@@ -82,15 +75,8 @@ void OverlayManager::drawOverlays()
   if (m_overlays.empty())
     return;
 
-  Manager* manager = Manager::getDefault();
-  if (!manager)
-    return;
-
-  os::Surface* windowSurface = manager->nativeWindow()->surface();
-  os::SurfaceLock lock(windowSurface);
-
   for (auto& overlay : *this)
-    overlay->captureOverlappedArea(windowSurface);
+    overlay->captureOverlappedArea();
 
   for (auto& overlay : *this)
     overlay->drawOverlay();
diff --git a/src/ui/slider.cpp b/src/ui/slider.cpp
index 01897a0f6..190de3291 100644
--- a/src/ui/slider.cpp
+++ b/src/ui/slider.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,7 +13,6 @@
 
 #include "base/clamp.h"
 #include "os/font.h"
-#include "ui/manager.h"
 #include "ui/message.h"
 #include "ui/size_hint_event.h"
 #include "ui/system.h"
diff --git a/src/ui/system.cpp b/src/ui/system.cpp
index b80e01f85..0077a6996 100644
--- a/src/ui/system.cpp
+++ b/src/ui/system.cpp
@@ -36,17 +36,15 @@ namespace ui {
 base::thread::native_id_type main_gui_thread;
 
 // Current mouse cursor type.
-
 static CursorType mouse_cursor_type = kOutsideDisplay;
 static const Cursor* mouse_cursor_custom = nullptr;
 static const Cursor* mouse_cursor = nullptr;
-static os::Window* mouse_window = nullptr;
+static Display* mouse_display = nullptr;
 static OverlayRef mouse_cursor_overlay = nullptr;
 static bool use_native_mouse_cursor = true;
 static bool support_native_custom_cursor = false;
 
 // Mouse information (button and position).
-
 static gfx::Point m_mouse_pos;
 static int mouse_cursor_scale = 1;
 
@@ -58,7 +56,9 @@ static void update_mouse_overlay(const Cursor* cursor)
 
   if (mouse_cursor && mouse_scares == 0) {
     if (!mouse_cursor_overlay) {
+      ASSERT(mouse_display);
       mouse_cursor_overlay = base::make_ref<Overlay>(
+        mouse_display,
         mouse_cursor->getSurface(),
         get_mouse_position(),
         Overlay::MouseZOrder);
@@ -83,20 +83,22 @@ static bool update_custom_native_cursor(const Cursor* cursor)
 
   // Check if we can use a custom native mouse in this platform
   if (support_native_custom_cursor &&
-      mouse_window) {
+      mouse_display) {
+    os::Window* nativeWindow = mouse_display->nativeWindow();
+
     if (cursor) {
-      result = mouse_window->setNativeMouseCursor(
+      result = nativeWindow->setNativeMouseCursor(
         // The surface is already scaled by guiscale()
         cursor->getSurface().get(),
         cursor->getFocus(),
         // We scale the cursor by the os::Display scale
-        mouse_window->scale() * mouse_cursor_scale);
+        nativeWindow->scale() * mouse_cursor_scale);
     }
     else if (mouse_cursor_type == kOutsideDisplay) {
-      result = mouse_window->setNativeMouseCursor(os::NativeCursor::Arrow);
+      result = nativeWindow->setNativeMouseCursor(os::NativeCursor::Arrow);
     }
     else {
-      result = mouse_window->setNativeMouseCursor(os::NativeCursor::Hidden);
+      result = nativeWindow->setNativeMouseCursor(os::NativeCursor::Hidden);
     }
   }
 
@@ -146,8 +148,8 @@ static void update_mouse_cursor()
   }
 
   // Set native cursor
-  if (mouse_window) {
-    bool ok = mouse_window->setNativeMouseCursor(nativeCursor);
+  if (mouse_display) {
+    bool ok = mouse_display->nativeWindow()->setNativeMouseCursor(nativeCursor);
 
     // It looks like the specific native cursor is not supported,
     // so we can should use the internal overlay (even when we
@@ -166,7 +168,8 @@ static void update_mouse_cursor()
   }
 
   // Try to use a custom native cursor if it's possible
-  if (nativeCursor == os::NativeCursor::Hidden &&
+  if (mouse_display &&
+      nativeCursor == os::NativeCursor::Hidden &&
       !update_custom_native_cursor(cursor)) {
     // Or an overlay as last resource
     update_mouse_overlay(cursor);
@@ -207,7 +210,7 @@ UISystem::~UISystem()
 
   details::exitWidgets();
 
-  _internal_set_mouse_window(nullptr);
+  _internal_set_mouse_display(nullptr);
   if (!update_custom_native_cursor(nullptr))
     update_mouse_overlay(nullptr);
 
@@ -215,29 +218,24 @@ UISystem::~UISystem()
   g_instance = nullptr;
 }
 
-void _internal_set_mouse_window(os::Window* window)
+void _internal_set_mouse_display(Display* display)
 {
   CursorType cursor = get_mouse_cursor();
   set_mouse_cursor(kNoCursor);
-  mouse_window = window;
-  if (window)
+  mouse_display = display;
+  if (display)
     set_mouse_cursor(cursor);  // Restore mouse cursor
 }
 
-int display_w()
+void _internal_free_mouse_display(Display* display)
 {
-  if (mouse_window)
-    return mouse_window->width() / mouse_window->scale();
-  else
-    return 1;
+  if (mouse_display == display)
+    _internal_set_mouse_display(nullptr);
 }
 
-int display_h()
+gfx::Size get_desktop_size()
 {
-  if (mouse_window)
-    return mouse_window->height() / mouse_window->scale();
-  else
-    return 1;
+  return Manager::getDefault()->display()->size();
 }
 
 void set_clipboard_text(const std::string& text)
@@ -331,8 +329,8 @@ const gfx::Point& get_mouse_position()
 
 void set_mouse_position(const gfx::Point& newPos)
 {
-  if (mouse_window)
-    mouse_window->setMousePosition(newPos);
+  if (mouse_display)
+    mouse_display->nativeWindow()->setMousePosition(newPos);
 
   _internal_set_mouse_position(newPos);
 }
diff --git a/src/ui/system.h b/src/ui/system.h
index 79c8842c3..cbede9855 100644
--- a/src/ui/system.h
+++ b/src/ui/system.h
@@ -16,12 +16,11 @@
 #include <functional>
 #include <string>
 
-namespace os { class Window; }
-
 namespace ui {
 
   class ClipboardDelegate;
   class Cursor;
+  class Display;
   class Widget;
 
   class UISystem {
@@ -41,8 +40,7 @@ namespace ui {
     ClipboardDelegate* m_clipboardDelegate;
   };
 
-  int display_w();
-  int display_h();
+  gfx::Size get_desktop_size();
 
   void set_clipboard_text(const std::string& text);
   bool get_clipboard_text(std::string& text);
@@ -61,7 +59,8 @@ namespace ui {
   void hide_mouse_cursor();
   void show_mouse_cursor();
 
-  void _internal_set_mouse_window(os::Window* window);
+  void _internal_set_mouse_display(Display* display);
+  void _internal_free_mouse_display(Display* display);
   void _internal_no_mouse_position();
   void _internal_set_mouse_position(const gfx::Point& newPos);
 
diff --git a/src/ui/tooltips.cpp b/src/ui/tooltips.cpp
index e108589f8..cf5815554 100644
--- a/src/ui/tooltips.cpp
+++ b/src/ui/tooltips.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -122,7 +122,11 @@ void TooltipManager::onTick()
     if (!arrowAlign)
       target.setOrigin(ui::get_mouse_position()+12*guiscale());
 
-    if (m_tipWindow->pointAt(arrowAlign, target)) {
+    if (m_tipWindow->pointAt(arrowAlign,
+                             target,
+                             m_target.widget->display())) {
+      // TODO create a native transparent window for the tooltip
+      m_tipWindow->setDisplay(m_target.widget->display());
       m_tipWindow->openWindow();
     }
     else {
@@ -161,7 +165,9 @@ void TipWindow::setCloseOnKeyDown(bool state)
   m_closeOnKeyDown = state;
 }
 
-bool TipWindow::pointAt(int arrowAlign, const gfx::Rect& target)
+bool TipWindow::pointAt(int arrowAlign,
+                        const gfx::Rect& target,
+                        const ui::Display* display)
 {
   // TODO merge this code with the new ui::fit_bounds() algorithm
 
@@ -212,8 +218,9 @@ bool TipWindow::pointAt(int arrowAlign, const gfx::Rect& target)
         break;
     }
 
-    x = base::clamp(x, 0, ui::display_w()-w);
-    y = base::clamp(y, 0, ui::display_h()-h);
+    auto displayBounds = display->bounds();
+    x = base::clamp(x, displayBounds.x, displayBounds.x2()-w);
+    y = base::clamp(y, displayBounds.y, displayBounds.y2()-h);
 
     if (m_target.intersects(gfx::Rect(x, y, w, h))) {
       switch (trycount) {
diff --git a/src/ui/tooltips.h b/src/ui/tooltips.h
index da5e990f0..cb9cf69c4 100644
--- a/src/ui/tooltips.h
+++ b/src/ui/tooltips.h
@@ -1,4 +1,5 @@
 // Aseprite UI Library
+// Copyright (C) 2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -18,6 +19,7 @@
 
 namespace ui {
 
+  class Display;
   class TextBox;
   class TipWindow;
 
@@ -70,7 +72,9 @@ namespace ui {
 
     // Returns false there is no enough screen space to show the
     // window.
-    bool pointAt(int arrowAlign, const gfx::Rect& target);
+    bool pointAt(int arrowAlign,
+                 const gfx::Rect& target,
+                 const ui::Display* display);
 
     TextBox* textBox() const { return m_textBox; }
 
diff --git a/src/ui/ui.h b/src/ui/ui.h
index c11df9cdd..5c49d9c40 100644
--- a/src/ui/ui.h
+++ b/src/ui/ui.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -19,6 +19,7 @@
 #include "ui/component.h"
 #include "ui/cursor.h"
 #include "ui/cursor_type.h"
+#include "ui/display.h"
 #include "ui/entry.h"
 #include "ui/event.h"
 #include "ui/fit_bounds.h"
diff --git a/src/ui/view.cpp b/src/ui/view.cpp
index 1d53cffc3..0403e1792 100644
--- a/src/ui/view.cpp
+++ b/src/ui/view.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,8 +13,8 @@
 
 #include "base/clamp.h"
 #include "gfx/size.h"
+#include "ui/display.h"
 #include "ui/intern.h"
-#include "ui/manager.h"
 #include "ui/message.h"
 #include "ui/move_region.h"
 #include "ui/resize_event.h"
@@ -28,8 +28,8 @@
 
 #ifdef DEBUG_SCROLL_EVENTS
 #include "base/thread.h"
-#include "os/display.h"
 #include "os/surface.h"
+#include "os/window.h"
 #endif
 
 #include <algorithm>
@@ -289,9 +289,9 @@ void View::onSetViewScroll(const gfx::Point& pt)
 
   // Remove invalid region in the screen (areas that weren't
   // re-painted yet)
-  Manager* manager = this->manager();
-  if (manager)
-    validRegion -= manager->getInvalidRegion();
+  Display* display = this->display();
+  if (display)
+    validRegion -= display->getInvalidRegion();
 
   // Add extra regions that cannot be scrolled (this can be customized
   // by subclassing ui::View). We use two ScrollRegionEvent, this
@@ -327,27 +327,25 @@ void View::onSetViewScroll(const gfx::Point& pt)
     invalidRegion -= movable;   // Remove the moved region as invalid
     movable.offset(-delta);
 
-    ui::move_region(manager, movable, delta.x, delta.y);
+    ui::move_region(display, movable, delta.x, delta.y);
   }
 
 #ifdef DEBUG_SCROLL_EVENTS
   // Paint invalid region with red fill
-  {
-    auto display = manager->getDisplay();
-    if (display)
-      display->invalidateRegion(
-        gfx::Region(gfx::Rect(0, 0, display_w(), display_h())));
+  if (auto nativeWindow = display->nativeWindow()) {
+    nativeWindow->invalidateRegion(gfx::Region(display->bounds()));
     base::this_thread::sleep_for(0.002);
     {
-      os::Surface* surface = display->getSurface();
+      os::Surface* surface = nativeWindow->surface();
       os::SurfaceLock lock(surface);
+      os::Paint p;
+      p.style(os::Paint::Fill);
+      p.color(gfx::rgba(255, 0, 0));
       for (const auto& rc : invalidRegion)
-        surface->fillRect(gfx::rgba(255, 0, 0), rc);
+        surface->drawRect(rc, p);
     }
-    if (display)
-      display->invalidateRegion(
-        gfx::Region(gfx::Rect(0, 0, display_w(), display_h())));
-    base::this_thread::sleep_for(0.002);
+    nativeWindow->invalidateRegion(gfx::Region(display->bounds()));
+    base::this_thread::sleep_for(0.02);
   }
 #endif
 
diff --git a/src/ui/widget.cpp b/src/ui/widget.cpp
index 61d88cee7..007ad1982 100644
--- a/src/ui/widget.cpp
+++ b/src/ui/widget.cpp
@@ -420,6 +420,14 @@ Manager* Widget::manager() const
   return Manager::getDefault();
 }
 
+Display* Widget::display() const
+{
+  if (Window* win = this->window())
+    return win->display();
+  else
+    return manager()->display();
+}
+
 int Widget::getChildIndex(Widget* child)
 {
   auto it = std::find(m_children.begin(), m_children.end(), child);
@@ -754,36 +762,31 @@ void Widget::getRegion(gfx::Region& region)
 
 void Widget::getDrawableRegion(gfx::Region& region, DrawableRegionFlags flags)
 {
-  Widget* window, *manager, *view;
-
   getRegion(region);
 
   // Cut the top windows areas
   if (flags & kCutTopWindows) {
-    window = this->window();
-    manager = (window ? window->manager(): nullptr);
+    Window* window = this->window();
+    Display* display = this->display();
 
-    while (manager) {
-      const WidgetsList& windows_list = manager->children();
-      WidgetsList::const_reverse_iterator it =
-        std::find(windows_list.rbegin(), windows_list.rend(), window);
+    const auto& uiWindows = display->getWindows();
 
-      if (!windows_list.empty() &&
-          window != windows_list.front() &&
-          it != windows_list.rend()) {
-        // Subtract the rectangles
-        for (++it; it != windows_list.rend(); ++it) {
-          if (!(*it)->isVisible())
-            continue;
+    // Reverse iterator
+    auto it = std::find(uiWindows.rbegin(),
+                        uiWindows.rend(), window);
 
-          Region reg1;
-          (*it)->getRegion(reg1);
-          region.createSubtraction(region, reg1);
-        }
+    if (!uiWindows.empty() &&
+        window != uiWindows.front() &&
+        it != uiWindows.rend()) {
+      // Subtract the rectangles of each window
+      for (++it; it != uiWindows.rend(); ++it) {
+        if (!(*it)->isVisible())
+          continue;
+
+        Region reg1;
+        (*it)->getRegion(reg1);
+        region -= reg1;
       }
-
-      window = manager->window();
-      manager = (window ? window->manager(): nullptr);
     }
   }
 
@@ -804,7 +807,7 @@ void Widget::getDrawableRegion(gfx::Region& region, DrawableRegionFlags flags)
         else {
           reg1.createIntersection(reg2, reg3);
         }
-        region.createSubtraction(region, reg1);
+        region -= reg1;
       }
     }
   }
@@ -813,36 +816,35 @@ void Widget::getDrawableRegion(gfx::Region& region, DrawableRegionFlags flags)
   if (!hasFlags(DECORATIVE)) {
     Widget* p = this->parent();
     while (p) {
-      region.createIntersection(
-        region, Region(p->childrenBounds()));
+      region &= Region(p->childrenBounds());
       p = p->parent();
     }
   }
   else {
     Widget* p = parent();
     if (p) {
-      region.createIntersection(
-        region, Region(p->bounds()));
+      region &= Region(p->bounds());
     }
   }
 
   // Limit to the manager area
-  window = this->window();
-  manager = (window ? window->manager(): nullptr);
+  {
+    Window* window = this->window();
+    Manager* manager = (window ? window->manager(): nullptr);
+    while (manager) {
+      View* view = View::getView(manager);
 
-  while (manager) {
-    view = View::getView(manager);
+      Rect cpos;
+      if (view)
+        cpos = static_cast<View*>(view)->viewportBounds();
+      else
+        cpos = manager->childrenBounds();
 
-    Rect cpos;
-    if (view)
-      cpos = static_cast<View*>(view)->viewportBounds();
-    else
-      cpos = manager->childrenBounds();
+      region &= Region(cpos);
 
-    region.createIntersection(region, Region(cpos));
-
-    window = manager->window();
-    manager = (window ? window->manager(): nullptr);
+      window = manager->window();
+      manager = (window ? window->manager(): nullptr);
+    }
   }
 }
 
@@ -980,6 +982,7 @@ void Widget::flushRedraw()
     processing.push(this);
   }
 
+  Display* display = this->display();
   Manager* manager = this->manager();
   ASSERT(manager);
   if (!manager)
@@ -1018,13 +1021,14 @@ void Widget::flushRedraw()
       for (c=0; c<nrects; ++c, ++it, --count) {
         // Create the draw message
         msg = new PaintMessage(count, *it);
+        msg->setDisplay(display);
         msg->setRecipient(widget);
 
         // Enqueue the draw message
         manager->enqueueMessage(msg);
       }
 
-      manager->addInvalidRegion(widget->m_updateRegion);
+      display->addInvalidRegion(widget->m_updateRegion);
       widget->m_updateRegion.clear();
     }
   }
@@ -1040,6 +1044,8 @@ void Widget::paint(Graphics* graphics,
   std::queue<Widget*> processing;
   processing.push(this);
 
+  Display* display = this->display();
+
   while (!processing.empty()) {
     Widget* widget = processing.front();
     processing.pop();
@@ -1059,17 +1065,17 @@ void Widget::paint(Graphics* graphics,
     region.createIntersection(region, drawRegion);
 
     Graphics graphics2(
+      display,
       base::AddRef(graphics->getInternalSurface()),
       widget->bounds().x,
       widget->bounds().y);
     graphics2.setFont(AddRef(widget->font()));
 
-    for (Region::const_iterator
-           it = region.begin(),
-           end = region.end(); it != end; ++it) {
-      IntersectClip clip(&graphics2, Rect(*it).offset(
-          -widget->bounds().x,
-          -widget->bounds().y));
+    for (const gfx::Rect& rc : region) {
+      IntersectClip clip(&graphics2,
+                         Rect(rc).offset(
+                           -widget->bounds().x,
+                           -widget->bounds().y));
       widget->paintEvent(&graphics2, isBg);
     }
   }
@@ -1089,14 +1095,22 @@ bool Widget::paintEvent(Graphics* graphics,
     enableFlags(HIDDEN);
 
     if (parent()) {
-      gfx::Region rgn(parent()->bounds());
-      rgn.createIntersection(
-        rgn,
-        gfx::Region(
+      if (parent()->display() == display()) {
+        gfx::Region rgn(parent()->bounds());
+        rgn &= gfx::Region(
           graphics->getClipBounds().offset(
             graphics->getInternalDeltaX(),
-            graphics->getInternalDeltaY())));
-      parent()->paint(graphics, rgn, true);
+            graphics->getInternalDeltaY()));
+        parent()->paint(graphics, rgn, true);
+      }
+      else {
+        // TODO clear surface with transparent color, the following
+        //      line doesn't work because we have to specify the
+        //      SkBlendMode::kSrc mode instead of
+        //      SkBlendMode::kSrcOver
+
+        //graphics->fillRect(gfx::rgba(0, 0, 0, 0), clientBounds());
+      }
     }
 
     disableFlags(HIDDEN);
@@ -1152,17 +1166,19 @@ void Widget::invalidateRegion(const Region& region)
 class DeleteGraphicsAndSurface {
 public:
   DeleteGraphicsAndSurface(const gfx::Rect& clip,
-                           const os::SurfaceRef& surface)
-    : m_pt(clip.origin()), m_surface(surface) {
+                           const os::SurfaceRef& surface,
+                           os::SurfaceRef& dst)
+    : m_pt(clip.origin())
+    , m_surface(surface)
+    , m_dst(dst) {
   }
 
   void operator()(Graphics* graphics) {
     {
-      os::Surface* dst = os::instance()->defaultWindow()->surface();
       os::SurfaceLock lockSrc(m_surface.get());
-      os::SurfaceLock lockDst(dst);
+      os::SurfaceLock lockDst(m_dst.get());
       m_surface->blitTo(
-        dst, 0, 0, m_pt.x, m_pt.y,
+        m_dst.get(), 0, 0, m_pt.x, m_pt.y,
         m_surface->width(), m_surface->height());
     }
     m_surface.reset();
@@ -1172,25 +1188,27 @@ public:
 private:
   gfx::Point m_pt;
   os::SurfaceRef m_surface;
+  os::SurfaceRef m_dst;
 };
 
 GraphicsPtr Widget::getGraphics(const gfx::Rect& clip)
 {
   GraphicsPtr graphics;
-  os::SurfaceRef surface;
-  os::Surface* defaultSurface = os::instance()->defaultWindow()->surface();
+  Display* display = this->display();
+  os::SurfaceRef dstSurface = AddRef(display->surface());
 
   // In case of double-buffering, we need to create the temporary
   // buffer only if the default surface is the screen.
-  if (isDoubleBuffered() && defaultSurface->isDirectToScreen()) {
-    surface = os::instance()->makeSurface(clip.w, clip.h);
-    graphics.reset(new Graphics(surface, -clip.x, -clip.y),
-                   DeleteGraphicsAndSurface(clip, surface));
+  if (isDoubleBuffered() && dstSurface->isDirectToScreen()) {
+    os::SurfaceRef surface =
+      os::instance()->makeSurface(clip.w, clip.h);
+    graphics.reset(new Graphics(display, surface, -clip.x, -clip.y),
+                   DeleteGraphicsAndSurface(clip, surface,
+                                            dstSurface));
   }
   // In other case, we can draw directly onto the screen.
   else {
-    surface = AddRef(defaultSurface);
-    graphics.reset(new Graphics(surface, bounds().x, bounds().y));
+    graphics.reset(new Graphics(display, dstSurface, bounds().x, bounds().y));
   }
 
   graphics->setFont(AddRef(font()));
diff --git a/src/ui/widget.h b/src/ui/widget.h
index eadd36d42..74f496e3c 100644
--- a/src/ui/widget.h
+++ b/src/ui/widget.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -29,6 +29,7 @@
 
 namespace ui {
 
+  class Display;
   class InitThemeEvent;
   class KeyMessage;
   class LoadLayoutEvent;
@@ -161,6 +162,7 @@ namespace ui {
     Window* window() const;
     Widget* parent() const { return m_parent; }
     Manager* manager() const;
+    Display* display() const;
 
     // Returns a list of children.
     const WidgetsList& children() const { return m_children; }
diff --git a/src/ui/window.cpp b/src/ui/window.cpp
index 8ef052b2d..d0c2e6435 100644
--- a/src/ui/window.cpp
+++ b/src/ui/window.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2020  Igara Studio S.A.
+// Copyright (C) 2018-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,6 +13,7 @@
 
 #include "gfx/size.h"
 #include "ui/button.h"
+#include "ui/display.h"
 #include "ui/graphics.h"
 #include "ui/intern.h"
 #include "ui/label.h"
@@ -107,6 +108,7 @@ protected:
 
 Window::Window(Type type, const std::string& text)
   : Widget(kWindowWidget)
+  , m_display(nullptr)
   , m_closer(nullptr)
   , m_titleLabel(nullptr)
   , m_closeButton(nullptr)
@@ -133,6 +135,27 @@ Window::~Window()
   manager()->_closeWindow(this, isVisible());
 }
 
+Display* Window::display() const
+{
+  if (m_display)
+    return m_display;
+  else if (auto man = manager())
+    return man->display();
+  else
+    return nullptr;
+}
+
+void Window::setDisplay(Display* display)
+{
+  if (m_display)
+    m_display->removeWindow(this);
+
+  m_display = display;
+
+  if (m_display)
+    m_display->addWindow(this);
+}
+
 void Window::setAutoRemap(bool state)
 {
   m_isAutoRemap = state;
@@ -658,12 +681,13 @@ void Window::moveWindow(const gfx::Rect& rect, bool use_blit)
     moveableRegion.createIntersection(oldDrawableRegion, reg1);
 
     // Move the window's graphics
-    ScreenGraphics g;
+    Display* display = this->display();
+    ScreenGraphics g(display);
     hide_mouse_cursor();
     {
       IntersectClip clip(&g, man_pos);
       if (clip) {
-        ui::move_region(manager, moveableRegion, dx, dy);
+        ui::move_region(display, moveableRegion, dx, dy);
       }
     }
     show_mouse_cursor();
diff --git a/src/ui/window.h b/src/ui/window.h
index 069264b9c..04b751b6e 100644
--- a/src/ui/window.h
+++ b/src/ui/window.h
@@ -1,4 +1,5 @@
 // Aseprite UI Library
+// Copyright (C) 2019-2021  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -27,6 +28,9 @@ namespace ui {
     explicit Window(Type type, const std::string& text = "");
     ~Window();
 
+    Display* display() const;
+    void setDisplay(Display* display);
+
     Widget* closer() const { return m_closer; }
 
     void setAutoRemap(bool state);
@@ -77,6 +81,7 @@ namespace ui {
     void limitSize(int* w, int* h);
     void moveWindow(const gfx::Rect& rect, bool use_blit);
 
+    Display* m_display;
     Widget* m_closer;
     Label* m_titleLabel;
     ButtonBase* m_closeButton;