Bug 1574592 - Add CompositorWidget::GetOpaqueWidgetRegion. r=mattwoodrow

This lets LayerManagerComposite and RendererOGL set the correct opaque region
on the native layer.

Differential Revision: https://phabricator.services.mozilla.com/D42401

--HG--
extra : moz-landing-system : lando

widget/CompositorWidget.h

@@ -252,6 +252,24 @@ class CompositorWidget {
    */
   virtual already_AddRefed<gfx::SourceSurface> EndBackBufferDrawing();
 
+#ifdef XP_MACOSX
+  /**
+   * Return the opaque region of the widget. This is racy and can only be used
+   * on macOS, where the widget works around the raciness.
+   * Bug 1576491 tracks fixing this properly.
+   * The problem with this method is that it can return values "from the future"
+   * - the compositor might be working on frame N but the widget will return its
+   * opaque region from frame N + 1.
+   * It is believed that this won't lead to visible glitches on macOS due to the
+   * SuspendAsyncCATransactions call when the vibrant region changes or when the
+   * window resizes. Whenever the compositor uses an opaque region that's a
+   * frame ahead, the result it renders won't be shown on the screen; instead,
+   * the next composite will happen with the correct display list, and that's
+   * what's shown on the screen once the FlushRendering call completes.
+   */
+  virtual LayoutDeviceIntRegion GetOpaqueWidgetRegion() { return {}; }
+#endif
+
   /**
    * Observe or unobserve vsync.
    */

widget/InProcessCompositorWidget.cpp

@@ -110,6 +110,12 @@ uintptr_t InProcessCompositorWidget::GetWidgetKey() {
 
 nsIWidget* InProcessCompositorWidget::RealWidget() { return mWidget; }
 
+#ifdef XP_MACOSX
+LayoutDeviceIntRegion InProcessCompositorWidget::GetOpaqueWidgetRegion() {
+  return mWidget->GetOpaqueWidgetRegion();
+}
+#endif
+
 void InProcessCompositorWidget::ObserveVsync(VsyncObserver* aObserver) {
   if (RefPtr<CompositorVsyncDispatcher> cvd =
           mWidget->GetCompositorVsyncDispatcher()) {

widget/InProcessCompositorWidget.h

@@ -38,6 +38,9 @@ class InProcessCompositorWidget : public CompositorWidget {
   virtual bool InitCompositor(layers::Compositor* aCompositor) override;
   virtual LayoutDeviceIntSize GetClientSize() override;
   virtual uint32_t GetGLFrameBufferFormat() override;
+#ifdef XP_MACOSX
+  virtual LayoutDeviceIntRegion GetOpaqueWidgetRegion() override;
+#endif
   virtual void ObserveVsync(VsyncObserver* aObserver) override;
   virtual uintptr_t GetWidgetKey() override;
 

widget/cocoa/nsChildView.h

@@ -568,6 +568,8 @@ class nsChildView final : public nsBaseWidget {
 
   virtual LayoutDeviceIntPoint GetClientOffset() override;
 
+  virtual LayoutDeviceIntRegion GetOpaqueWidgetRegion() override;
+
   void DispatchAPZWheelInputEvent(mozilla::InputData& aEvent, bool aCanTriggerSwipe);
   nsEventStatus DispatchAPZInputEvent(mozilla::InputData& aEvent);
 

widget/cocoa/nsChildView.mm

@@ -1590,6 +1590,11 @@ LayoutDeviceIntPoint nsChildView::WidgetToScreenOffset() {
   NS_OBJC_END_TRY_ABORT_BLOCK_RETURN(LayoutDeviceIntPoint(0, 0));
 }
 
+LayoutDeviceIntRegion nsChildView::GetOpaqueWidgetRegion() {
+  auto opaqueRegion = mOpaqueRegion.Lock();
+  return *opaqueRegion;
+}
+
 nsresult nsChildView::SetTitle(const nsAString& title) {
   // child views don't have titles
   return NS_OK;

widget/nsBaseWidget.h

@@ -476,6 +476,9 @@ class nsBaseWidget : public nsIWidget, public nsSupportsWeakReference {
   }
   virtual uint32_t GetGLFrameBufferFormat();
   virtual bool CompositorInitiallyPaused() { return false; }
+#ifdef XP_MACOSX
+  virtual LayoutDeviceIntRegion GetOpaqueWidgetRegion() { return {}; }
+#endif
 
  protected:
   void ResolveIconName(const nsAString& aIconName, const nsAString& aIconSuffix,