[lua] Add initial version Dialog:canvas() (aseprite/api#87)

Right now it just creates a plain widget, but now we can specify
hexpand/vexpand arguments too so we can create a canvas with a fixed
size or with dynamic size (e.g. to use the whole dialog client area).

The onpaint event is not functional yet.

src/app/CMakeLists.txt

@@ -165,6 +165,7 @@ if(ENABLE_SCRIPTING)
     script/app_fs_object.cpp
     script/app_object.cpp
     script/brush_class.cpp
+    script/canvas_widget.cpp
     script/cel_class.cpp
     script/cels_class.cpp
     script/color_class.cpp

src/app/script/canvas_widget.cpp

@@ -0,0 +1,80 @@
+// Aseprite
+// Copyright (c) 2022  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#include "app/script/canvas_widget.h"
+
+#include "app/ui/skin/skin_theme.h"
+#include "os/system.h"
+#include "ui/message.h"
+#include "ui/paint_event.h"
+#include "ui/resize_event.h"
+#include "ui/size_hint_event.h"
+
+#ifdef ENABLE_UI
+
+namespace app {
+namespace script {
+
+// static
+ui::WidgetType Canvas::Type()
+{
+  static ui::WidgetType type = ui::kGenericWidget;
+  if (type == ui::kGenericWidget)
+    type = ui::register_widget_type();
+  return type;
+}
+
+Canvas::Canvas() : ui::Widget(Type())
+{
+}
+
+void Canvas::onInitTheme(ui::InitThemeEvent& ev)
+{
+  Widget::onInitTheme(ev);
+
+  gfx::Color bg;
+  if (auto theme = skin::SkinTheme::get(this))
+    bg = theme->colors.windowFace();
+  else
+    bg = gfx::rgba(0, 0, 0);
+  setBgColor(bg);
+}
+
+void Canvas::onResize(ui::ResizeEvent& ev)
+{
+  Widget::onResize(ev);
+  if (os::instance() && !ev.bounds().isEmpty()) {
+    const int w = ev.bounds().w;
+    const int h = ev.bounds().h;
+
+    if (!m_surface ||
+        m_surface->width() != w ||
+        m_surface->height() != h) {
+      m_surface = os::instance()->makeSurface(w, h);
+
+      os::Paint p;
+      p.color(bgColor());
+      m_surface->drawRect(m_surface->bounds(), p);
+    }
+  }
+  else
+    m_surface.reset();
+}
+
+void Canvas::onPaint(ui::PaintEvent& ev)
+{
+  Paint(ev);
+
+  auto g = ev.graphics();
+  const gfx::Rect rc = clientBounds();
+  if (m_surface)
+    g->drawSurface(m_surface.get(), rc.x, rc.y);
+}
+
+} // namespace script
+} // namespace app
+
+#endif // ENABLE_UI

src/app/script/canvas_widget.h

@@ -0,0 +1,38 @@
+// Aseprite
+// Copyright (c) 2022  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifndef APP_SCRIPT_CANVAS_H_INCLUDED
+#define APP_SCRIPT_CANVAS_H_INCLUDED
+#pragma once
+
+#include "os/surface.h"
+#include "ui/widget.h"
+
+namespace app {
+namespace script {
+
+// The canvas widget of a Dialog() created with Dialog:canvas{ ... }
+// This is a generic widget where all its events can be listened.
+class Canvas : public ui::Widget {
+public:
+  static ui::WidgetType Type();
+
+  Canvas();
+
+  obs::signal<void(ui::PaintEvent&)> Paint;
+
+private:
+  void onInitTheme(ui::InitThemeEvent& ev) override;
+  void onResize(ui::ResizeEvent& ev) override;
+  void onPaint(ui::PaintEvent& ev) override;
+
+  os::SurfaceRef m_surface;
+};
+
+} // namespace script
+} // namespace app
+
+#endif

src/app/script/dialog_class.cpp

@@ -13,6 +13,7 @@
 #include "app/color.h"
 #include "app/color_utils.h"
 #include "app/file_selector.h"
+#include "app/script/canvas_widget.h"
 #include "app/script/engine.h"
 #include "app/script/luacpp.h"
 #include "app/ui/color_button.h"
@@ -334,6 +335,9 @@ int Dialog_add_widget(lua_State* L, Widget* widget)
   const char* label = nullptr;
   std::string id;
   bool visible = true;
+  bool hexpand = true;
+  // Canvas is vertically expansive by default too
+  bool vexpand = (widget->type() == Canvas::Type());
 
   // This is to separate different kind of widgets without label in
   // different rows.
@@ -380,6 +384,15 @@ int Dialog_add_widget(lua_State* L, Widget* widget)
       widget->setVisible(visible);
     }
     lua_pop(L, 1);
+
+    // Expand horizontally/vertically, it allows to indicate that a
+    // specific widget is not expansive (e.g. a canvas with a fixed
+    // size)
+    type = lua_getfield(L, 2, "hexpand");
+    type = lua_getfield(L, 2, "vexpand");
+    if (type != LUA_TNIL) hexpand = lua_toboolean(L, -2);
+    if (type != LUA_TNIL) vexpand = lua_toboolean(L, -1);
+    lua_pop(L, 2);
   }
 
   if (label || !dlg->hbox) {
@@ -398,11 +411,15 @@ int Dialog_add_widget(lua_State* L, Widget* widget)
     auto hbox = new ui::HBox;
     if (widget->type() == ui::kButtonWidget)
       hbox->enableFlags(ui::HOMOGENEOUS);
-    dlg->grid.addChildInCell(hbox, 1, 1, ui::HORIZONTAL | ui::TOP);
+
+    dlg->grid.addChildInCell(
+      hbox, 1, 1,
+      ui::HORIZONTAL | (vexpand ? ui::VERTICAL: ui::TOP));
+
     dlg->hbox = hbox;
   }
 
-  widget->setExpansive(true);
+  widget->setExpansive(hexpand);
   dlg->hbox->addChild(widget);
 
   lua_pushvalue(L, 1);
@@ -872,6 +889,43 @@ int Dialog_file(lua_State* L)
   return Dialog_add_widget(L, widget);
 }
 
+int Dialog_canvas(lua_State* L)
+{
+  auto widget = new Canvas;
+
+  if (lua_istable(L, 2)) {
+    gfx::Size sz(0, 0);
+
+    int type = lua_getfield(L, 2, "width");
+    if (type != LUA_TNIL) {
+      sz.w = lua_tointegerx(L, -1, nullptr);
+    }
+    lua_pop(L, 1);
+
+    type = lua_getfield(L, 2, "height");
+    if (type != LUA_TNIL) {
+      sz.h = lua_tointegerx(L, -1, nullptr);
+    }
+    lua_pop(L, 1);
+
+    widget->setSizeHint(sz);
+
+    if (lua_istable(L, 2)) {
+      int type = lua_getfield(L, 2, "onpaint");
+      if (type == LUA_TFUNCTION) {
+        Dialog_connect_signal(
+          L, 1, widget->Paint,
+          [](lua_State* L, ui::PaintEvent& ev) {
+            // TODO
+          });
+      }
+      lua_pop(L, 1);
+    }
+  }
+
+  return Dialog_add_widget(L, widget);
+}
+
 int Dialog_modify(lua_State* L)
 {
   auto dlg = get_obj<Dialog>(L, 1);
@@ -1275,6 +1329,7 @@ const luaL_Reg Dialog_methods[] = {
   { "color", Dialog_color },
   { "shades", Dialog_shades },
   { "file", Dialog_file },
+  { "canvas", Dialog_canvas },
   { "modify", Dialog_modify },
   { nullptr, nullptr }
 };