Bug 1705877 - Add support for scaled cursors on GTK. r=stransky

I had overlooked the way to achieve this. This is possible using cairo
surfaces, but they only support integer scale factors, so we ceil and
potentially rasterize the image to a bigger size if needed.

Differential Revision: https://phabricator.services.mozilla.com/D112477

widget/gtk/WidgetStyleCache.cpp

@@ -515,16 +515,8 @@ static void LoadWidgetIconPixbuf(GtkWidget* aWidgetIcon) {
   gtk_icon_size_lookup(gtkIconSize, &iconWidth, &iconHeight);
 
   /* Those are available since Gtk+ 3.10 as well as GtkHeaderBar */
-  static auto sGtkIconThemeLookupIconForScalePtr =
-      (GtkIconInfo *
-       (*)(GtkIconTheme*, const gchar*, gint, gint, GtkIconLookupFlags))
-          dlsym(RTLD_DEFAULT, "gtk_icon_theme_lookup_icon_for_scale");
-  static auto sGdkCairoSurfaceCreateFromPixbufPtr =
-      (cairo_surface_t * (*)(const GdkPixbuf*, int, GdkWindow*))
-          dlsym(RTLD_DEFAULT, "gdk_cairo_surface_create_from_pixbuf");
-
   for (int scale = 1; scale < ICON_SCALE_VARIANTS + 1; scale++) {
-    GtkIconInfo* gtkIconInfo = sGtkIconThemeLookupIconForScalePtr(
+    GtkIconInfo* gtkIconInfo = gtk_icon_theme_lookup_icon_for_scale(
         gtk_icon_theme_get_default(), iconName, iconWidth, scale,
         (GtkIconLookupFlags)0);
 
@@ -539,7 +531,7 @@ static void LoadWidgetIconPixbuf(GtkWidget* aWidgetIcon) {
     g_object_unref(G_OBJECT(gtkIconInfo));
 
     cairo_surface_t* iconSurface =
-        sGdkCairoSurfaceCreateFromPixbufPtr(iconPixbuf, scale, nullptr);
+        gdk_cairo_surface_create_from_pixbuf(iconPixbuf, scale, nullptr);
     g_object_unref(iconPixbuf);
 
     nsAutoCString surfaceName;

widget/gtk/nsWindow.cpp

@@ -2388,18 +2388,11 @@ static GdkCursor* GetCursorForImage(const nsIWidget::Cursor& aCursor) {
   if (!aCursor.IsCustom()) {
     return nullptr;
   }
-  // FIXME: GTK doesn't provide an API for custom cursors that have more than
-  // native resolution, so this will scale the image instead, which is slightly
-  // unfortunate.
   nsIntSize size = nsIWidget::CustomCursorSize(aCursor);
-  GdkPixbuf* pixbuf =
-      nsImageToPixbuf::ImageToPixbuf(aCursor.mContainer, Some(size));
-  if (!pixbuf) {
-    return nullptr;
-  }
 
-  auto CleanupPixBuf =
-      mozilla::MakeScopeExit([&]() { g_object_unref(pixbuf); });
+  // NOTE: GTK only allows integer scale factors, so we ceil to the closest
+  // scale factor and then tell gtk to scale it down.
+  int32_t gtkScale = std::ceil(aCursor.mResolution);
 
   // Reject cursors greater than 128 pixels in some direction, to prevent
   // spoofing.
@@ -2412,6 +2405,13 @@ static GdkCursor* GetCursorForImage(const nsIWidget::Cursor& aCursor) {
     return nullptr;
   }
 
+  nsIntSize rasterSize = size * gtkScale;
+  GdkPixbuf* pixbuf =
+      nsImageToPixbuf::ImageToPixbuf(aCursor.mContainer, Some(rasterSize));
+  if (!pixbuf) {
+    return nullptr;
+  }
+
   // Looks like all cursors need an alpha channel (tested on Gtk 2.4.4). This
   // is of course not documented anywhere...
   // So add one if there isn't one yet
@@ -2424,8 +2424,20 @@ static GdkCursor* GetCursorForImage(const nsIWidget::Cursor& aCursor) {
     }
   }
 
-  return gdk_cursor_new_from_pixbuf(gdk_display_get_default(), pixbuf,
-                                    aCursor.mHotspotX, aCursor.mHotspotY);
+  auto CleanupPixBuf =
+      mozilla::MakeScopeExit([&]() { g_object_unref(pixbuf); });
+
+  cairo_surface_t* surface =
+      gdk_cairo_surface_create_from_pixbuf(pixbuf, gtkScale, nullptr);
+  if (!surface) {
+    return nullptr;
+  }
+
+  auto CleanupSurface =
+      mozilla::MakeScopeExit([&]() { cairo_surface_destroy(surface); });
+
+  return gdk_cursor_new_from_surface(gdk_display_get_default(), surface,
+                                     aCursor.mHotspotX, aCursor.mHotspotY);
 }
 
 void nsWindow::SetCursor(const Cursor& aCursor) {