Avoid capturing the mouse from widgets in background windows

This avoids clicking buttons that are not in the foreground/modal
window. At the same time the onBroadcastMouseMessage() functionality
was expanded in such a way that added widgets to the broadcast are the
only ones allowed to re-capture the mouse (even if they are not in the
current foreground window). This is required so the Editor can be
scrolled when we are visualizing a Filter window with preview.

New functions added to simplify some code:

* Manager::transferAsMouseDownMessage()
* Manager::allowCapture()
* base::contains()

Related to #4963 and #4973.

laf

@@ -1 +1 @@
-Subproject commit 339a0fa13584853bda8559de486e715e743a5763
+Subproject commit 65829107c838817987f3cf6374cc68c583e5d538

src/app/ui/font_entry.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (c) 2024  Igara Studio S.A.
+// Copyright (c) 2024-2025  Igara Studio S.A.
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
@@ -51,18 +51,12 @@ bool FontEntry::FontFace::onProcessMessage(Message* msg)
         MouseMessage* mouseMsg = static_cast<MouseMessage*>(msg);
         const gfx::Point screenPos = mouseMsg->display()->nativeWindow()->pointToScreen(
           mouseMsg->position());
-        Widget* pick = manager()->pickFromScreenPos(screenPos);
+        Manager* mgr = manager();
+        Widget* pick = mgr->pickFromScreenPos(screenPos);
         Widget* target = m_popup->getListBox();
 
         if (pick && (pick == target || pick->hasAncestor(target))) {
-          releaseMouse();
+          mgr->transferAsMouseDownMessage(this, pick, mouseMsg);
-
-          MouseMessage mouseMsg2(kMouseDownMessage,
-                                 *mouseMsg,
-                                 mouseMsg->positionForDisplay(pick->display()));
-          mouseMsg2.setRecipient(pick);
-          mouseMsg2.setDisplay(pick->display());
-          pick->sendMessage(&mouseMsg2);
           return true;
         }
       }

src/app/ui/toolbar.cpp

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -266,17 +266,10 @@ bool ToolBar::onProcessMessage(Message* msg)
       // mouse over the ToolBar.
       if (hasCapture()) {
         MouseMessage* mouseMsg = static_cast<MouseMessage*>(msg);
-        Widget* pick = manager()->pickFromScreenPos(mouseMsg->screenPosition());
+        Manager* mgr = manager();
+        Widget* pick = mgr->pickFromScreenPos(mouseMsg->screenPosition());
         if (ToolStrip* strip = dynamic_cast<ToolStrip*>(pick)) {
-          releaseMouse();
+          mgr->transferAsMouseDownMessage(this, strip, mouseMsg);
-
-          MouseMessage* mouseMsg2 = new MouseMessage(
-            kMouseDownMessage,
-            *mouseMsg,
-            mouseMsg->positionForDisplay(strip->display()));
-          mouseMsg2->setRecipient(strip);
-          mouseMsg2->setDisplay(strip->display());
-          manager()->enqueueMessage(mouseMsg2);
         }
       }
       break;
@@ -755,16 +748,10 @@ bool ToolBar::ToolStrip::onProcessMessage(Message* msg)
         if (m_hotTool)
           m_toolbar->selectTool(m_hotTool);
 
-        Widget* pick = manager()->pickFromScreenPos(mouseMsg->screenPosition());
+        Manager* mgr = manager();
+        Widget* pick = mgr->pickFromScreenPos(mouseMsg->screenPosition());
         if (ToolBar* bar = dynamic_cast<ToolBar*>(pick)) {
-          releaseMouse();
+          mgr->transferAsMouseDownMessage(this, bar, mouseMsg);
-
-          MouseMessage* mouseMsg2 = new MouseMessage(kMouseDownMessage,
-                                                     *mouseMsg,
-                                                     mouseMsg->positionForDisplay(pick->display()));
-          mouseMsg2->setRecipient(bar);
-          mouseMsg2->setDisplay(pick->display());
-          manager()->enqueueMessage(mouseMsg2);
         }
       }
       break;

src/ui/combobox.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2023  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -503,18 +503,17 @@ bool ComboBoxEntry::onProcessMessage(Message* msg)
         MouseMessage* mouseMsg = static_cast<MouseMessage*>(msg);
         gfx::Point screenPos = mouseMsg->display()->nativeWindow()->pointToScreen(
           mouseMsg->position());
-        Widget* pick = manager()->pickFromScreenPos(screenPos);
+        Manager* mgr = manager();
+        Widget* pick = mgr->pickFromScreenPos(screenPos);
         Widget* listbox = m_comboBox->m_listbox;
 
         if (pick != nullptr && (pick == listbox || pick->hasAncestor(listbox))) {
-          releaseMouse();
+          mgr->transferAsMouseDownMessage(this,
-
+                                          pick,
-          MouseMessage mouseMsg2(kMouseDownMessage,
+                                          mouseMsg,
-                                 *mouseMsg,
+                                          // Send the message right now, if we enqueue
-                                 mouseMsg->positionForDisplay(pick->display()));
+                                          // the message the popup window is closed.
-          mouseMsg2.setRecipient(pick);
+                                          true);
-          mouseMsg2.setDisplay(pick->display());
-          pick->sendMessage(&mouseMsg2);
           return true;
         }
       }

src/ui/int_entry.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019-2022  Igara Studio S.A.
+// Copyright (C) 2019-2025  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -89,17 +89,11 @@ bool IntEntry::onProcessMessage(Message* msg)
     case kMouseMoveMessage:
       if (hasCapture()) {
         MouseMessage* mouseMsg = static_cast<MouseMessage*>(msg);
-        Widget* pick = manager()->pickFromScreenPos(
+        Manager* mgr = manager();
+        Widget* pick = mgr->pickFromScreenPos(
           display()->nativeWindow()->pointToScreen(mouseMsg->position()));
         if (pick == m_slider.get()) {
-          releaseMouse();
+          mgr->transferAsMouseDownMessage(this, pick, mouseMsg);
-
-          MouseMessage mouseMsg2(kMouseDownMessage,
-                                 *mouseMsg,
-                                 mouseMsg->positionForDisplay(pick->display()));
-          mouseMsg2.setRecipient(pick);
-          mouseMsg2.setDisplay(pick->display());
-          pick->sendMessage(&mouseMsg2);
         }
       }
       break;

src/ui/manager.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -13,6 +13,7 @@
 // #define DEBUG_PAINT_MESSAGES      1
 // #define LIMIT_DISPATCH_TIME       1
 #define GARBAGE_TRACE(...) // TRACE(__VA_ARGS__)
+#define CAPTURE_TRACE(...) // TRACE(__VA_ARGS__)
 
 #ifdef HAVE_CONFIG_H
   #include "config.h"
@@ -21,6 +22,8 @@
 #include "ui/manager.h"
 
 #include "base/concurrent_queue.h"
+#include "base/contains.h"
+#include "base/remove_from_container.h"
 #include "base/scoped_value.h"
 #include "base/thread.h"
 #include "base/time.h"
@@ -183,8 +186,7 @@ os::Hit handle_native_hittest(os::Window* osWindow, const gfx::Point& pos)
 bool Manager::widgetAssociatedToManager(Widget* widget)
 {
   return (focus_widget == widget || mouse_widget == widget || capture_widget == widget ||
-          std::find(mouse_widgets_list.begin(), mouse_widgets_list.end(), widget) !=
+          base::contains(mouse_widgets_list, widget));
-            mouse_widgets_list.end());
 }
 
 Manager::Manager(const os::WindowRef& nativeWindow)
@@ -889,12 +891,12 @@ void Manager::enqueueMessage(Message* msg)
     concurrent_msg_queue.push(msg);
 }
 
-Window* Manager::getTopWindow()
+Window* Manager::getTopWindow() const
 {
   return static_cast<Window*>(UI_FIRST_WIDGET(children()));
 }
 
-Window* Manager::getDesktopWindow()
+Window* Manager::getDesktopWindow() const
 {
   for (auto child : children()) {
     Window* window = static_cast<Window*>(child);
@@ -904,7 +906,7 @@ Window* Manager::getDesktopWindow()
   return nullptr;
 }
 
-Window* Manager::getForegroundWindow()
+Window* Manager::getForegroundWindow() const
 {
   for (auto child : children()) {
     Window* window = static_cast<Window*>(child);
@@ -1033,8 +1035,33 @@ void Manager::setMouse(Widget* widget)
   }
 }
 
-void Manager::setCapture(Widget* widget)
+void Manager::setCapture(Widget* widget, bool force)
 {
+  ASSERT(widget);
+  if (!widget)
+    return;
+
+  CAPTURE_TRACE("Manager::setCapture %s\n", typeid(*widget).name());
+  if (!force &&
+      // The given "widget" cannot capture the mouse if it's not
+      // "clickable".  The definition of "clickable" generally means
+      // that the widget is in the current foreground/modal window, or
+      // in the desktop window (or in any floating non-modal window).
+      // But it can also be in a top window, e.g. a combobox popup.
+      !isWidgetClickable(widget) &&
+      // In some special cases, a widget transfers a mouse message to
+      // another widget which doesn't belong to the current foreground
+      // modal window, this is done using onBroadcastMouseMessage()
+      // and/or transferAsMouseDownMessage(), so here we allow capturing
+      // the mouse from widgets inside the "mouse_widgets_list"
+      // (widgets that are allowed to capture the mouse / added with
+      // allowCapture() function).
+      (widget != mouse_widget && !base::contains(mouse_widgets_list, widget))) {
+    CAPTURE_TRACE("-> FILTERED!\n");
+    return;
+  }
+  CAPTURE_TRACE("-> OK\n");
+
   // To set the capture, we set first the mouse_widget (because
   // mouse_widget shouldn't be != capture_widget)
   setMouse(widget);
@@ -1048,6 +1075,13 @@ void Manager::setCapture(Widget* widget)
     display->nativeWindow()->captureMouse();
 }
 
+void Manager::allowCapture(Widget* widget)
+{
+  ASSERT(widget);
+  if (!base::contains(mouse_widgets_list, widget))
+    mouse_widgets_list.push_back(widget);
+}
+
 // Sets the focus to the "magnetic" widget inside the window
 void Manager::attractFocus(Widget* widget)
 {
@@ -1082,6 +1116,8 @@ void Manager::freeMouse()
 void Manager::freeCapture()
 {
   if (capture_widget) {
+    CAPTURE_TRACE("Manager::freeCapture() %s\n", typeid(*capture_widget).name());
+
     Display* display = capture_widget->display();
 
     capture_widget->disableFlags(HAS_CAPTURE);
@@ -1113,9 +1149,7 @@ void Manager::freeWidget(Widget* widget)
   if (widget->hasMouse() || (widget == mouse_widget))
     freeMouse();
 
-  auto it = std::find(mouse_widgets_list.begin(), mouse_widgets_list.end(), widget);
+  base::remove_from_container(mouse_widgets_list, widget);
-  if (it != mouse_widgets_list.end())
-    mouse_widgets_list.erase(it);
 
   ASSERT(!Manager::widgetAssociatedToManager(widget));
 }
@@ -1279,6 +1313,53 @@ Widget* Manager::pickFromScreenPos(const gfx::Point& screenPos) const
   return Widget::pickFromScreenPos(screenPos);
 }
 
+void Manager::transferAsMouseDownMessage(Widget* from,
+                                         Widget* to,
+                                         const MouseMessage* mouseMsg,
+                                         const bool sendNow)
+{
+  ASSERT(to);
+  ASSERT(from);
+
+  // Remove the capture from the "from" widget.
+  if (from->hasCapture())
+    from->releaseMouse();
+
+  // Allow the "to" widget to re-capture the mouse.
+  allowCapture(to);
+
+  // We enqueue a copy of the mouse message but as a kMouseDownMessage.
+  auto mouseMsg2 = std::make_unique<MouseMessage>(kMouseDownMessage,
+                                                  *mouseMsg,
+                                                  mouseMsg->positionForDisplay(to->display()));
+  mouseMsg2->setRecipient(to);
+  mouseMsg2->setDisplay(to->display());
+
+  if (sendNow)
+    to->sendMessage(mouseMsg2.get());
+  else
+    enqueueMessage(mouseMsg2.release());
+}
+
+bool Manager::isWidgetClickable(const Widget* widget) const
+{
+  Window* widgetWindow = widget->window();
+  if (!widgetWindow)
+    return false;
+
+  for (auto* child : children()) {
+    Window* window = static_cast<Window*>(child);
+
+    if (widgetWindow == window)
+      return true;
+
+    if (window->isForeground() || window->isDesktop())
+      break;
+  }
+
+  return false;
+}
+
 void Manager::_closingAppWithException()
 {
   redrawState = RedrawState::ClosingApp;

src/ui/manager.h

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -72,9 +72,9 @@ public:
   void addToGarbage(Widget* widget);
   void collectGarbage();
 
-  Window* getTopWindow();
+  Window* getTopWindow() const;
-  Window* getDesktopWindow();
+  Window* getDesktopWindow() const;
-  Window* getForegroundWindow();
+  Window* getForegroundWindow() const;
   Display* getForegroundDisplay();
 
   Widget* getFocus();
@@ -83,7 +83,7 @@ public:
 
   void setFocus(Widget* widget);
   void setMouse(Widget* widget);
-  void setCapture(Widget* widget);
+  void setCapture(Widget* widget, bool force = false);
   void attractFocus(Widget* widget);
   void focusFirstChild(Widget* widget);
   void freeFocus();
@@ -107,6 +107,30 @@ public:
 
   Widget* pickFromScreenPos(const gfx::Point& screenPos) const override;
 
+  // Transfers the given MouseMessage received "from" (generally a
+  // kMouseMoveMessage) to the given "to" widget, sending a copy of
+  // the message but changing its type to kMouseDownMessage. By
+  // default it enqueues the message.
+  //
+  // If "from" has the mouse capture, it will be released as it is
+  // highly probable that the "to" widget will recapture the mouse
+  // again.
+  //
+  // This is used in cases were the user presses the mouse button on
+  // one widget, and then drags the mouse to another widget. With this
+  // we can transfer the mouse capture between widgets (from -> to)
+  // simulating a kMouseDownMessage for the new widget "to".
+  void transferAsMouseDownMessage(Widget* from,
+                                  Widget* to,
+                                  const MouseMessage* mouseMsg,
+                                  bool sendNow = false);
+
+  // Returns true if the widget is accessible with the mouse, i.e. the
+  // widget is in the current foreground window (or a top window above
+  // the foreground, e.g. a combobox popup), or there is no foreground
+  // window and the widget is in the desktop window.
+  bool isWidgetClickable(const Widget* widget) const;
+
   void _openWindow(Window* window, bool center);
   void _closeWindow(Window* window, bool redraw_background);
   void _runModalWindow(Window* window);
@@ -164,6 +188,7 @@ private:
                           const double magnification);
   bool handleWindowZOrder();
   void updateMouseWidgets(const gfx::Point& mousePos, Display* display);
+  void allowCapture(Widget* widget);
 
   int pumpQueue();
   bool sendMessageToWidget(Message* msg, Widget* widget);

src/ui/view.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -186,7 +186,7 @@ void View::updateView(const bool restoreScrollPos)
   // Restore the mouse capture if it changed, which means that a
   // scroll bar (when it was temporarily removed) lost the capture.
   if (man && man->getCapture() != mouseCapture && mouseCapture->isVisible())
-    man->setCapture(mouseCapture);
+    man->setCapture(mouseCapture, true); // Force the capture
 }
 
 Viewport* View::viewport()

src/ui/widget.cpp

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -1507,22 +1507,15 @@ void Widget::releaseMouse()
   }
 }
 
-bool Widget::offerCapture(ui::MouseMessage* mouseMsg, int widget_type)
+bool Widget::offerCapture(ui::MouseMessage* mouseMsg, const WidgetType widgetType)
 {
   if (hasCapture()) {
     const gfx::Point screenPos = mouseMsg->display()->nativeWindow()->pointToScreen(
       mouseMsg->position());
-    auto man = manager();
+    Manager* mgr = manager();
-    Widget* pick = (man ? man->pickFromScreenPos(screenPos) : nullptr);
+    Widget* pick = (mgr ? mgr->pickFromScreenPos(screenPos) : nullptr);
-    if (pick && pick != this && pick->type() == widget_type) {
+    if (pick && pick != this && pick->type() == widgetType) {
-      releaseMouse();
+      mgr->transferAsMouseDownMessage(this, pick, mouseMsg);
-
-      MouseMessage* mouseMsg2 = new MouseMessage(kMouseDownMessage,
-                                                 *mouseMsg,
-                                                 mouseMsg->positionForDisplay(pick->display()));
-      mouseMsg2->setDisplay(pick->display());
-      mouseMsg2->setRecipient(pick);
-      man->enqueueMessage(mouseMsg2);
       return true;
     }
   }

src/ui/widget.h

@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2018-2024  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -336,6 +336,11 @@ public:
 
   void requestFocus();
   void releaseFocus();
+
+  // Captures the mouse to continue receiving its messages until we
+  // release the capture. Useful for widgets with painting-like
+  // capabilities, where we want to keep track of the mouse until the
+  // user releases the mouse button, or drag-and-drop behaviors.
   void captureMouse();
   void releaseMouse();
 
@@ -371,9 +376,9 @@ public:
   // the widget bounds.
   gfx::Point mousePosInClientBounds() const { return toClient(mousePosInDisplay()); }
 
-  // Offer the capture to widgets of the given type. Returns true if
+  // Offers the capture to widgets of the given type. Returns true if
   // the capture was passed to other widget.
-  bool offerCapture(MouseMessage* mouseMsg, int widget_type);
+  bool offerCapture(MouseMessage* mouseMsg, WidgetType widgetType);
 
   // Returns lower-case letter that represet the mnemonic of the widget
   // (the underscored character, i.e. the letter after & symbol).