Bug 1343450 - Convert nsDisplayCanvasBackgroundColor to WebRenderDisplayItemLayer. r=mattwoodrow

gfx/thebes/gfxPrefs.h

@@ -469,6 +469,7 @@ private:
   DECL_GFX_PREF(Live, "layers.advanced.image-layers",          LayersAllowImageLayers, bool, false);
   DECL_GFX_PREF(Live, "layers.advanced.outline-layers",        LayersAllowOutlineLayers, bool, false);
   DECL_GFX_PREF(Live, "layers.advanced.text-layers",           LayersAllowTextLayers, bool, false);
+  DECL_GFX_PREF(Live, "layers.advanced.canvas-background-color", LayersAllowCanvasBackgroundColorLayers, bool, false);
   DECL_GFX_PREF(Once, "layers.amd-switchable-gfx.enabled",     LayersAMDSwitchableGfxEnabled, bool, false);
   DECL_GFX_PREF(Once, "layers.async-pan-zoom.enabled",         AsyncPanZoomEnabledDoNotUseDirectly, bool, true);
   DECL_GFX_PREF(Once, "layers.async-pan-zoom.separate-event-thread", AsyncPanZoomSeparateEventThread, bool, false);

layout/generic/nsCanvasFrame.cpp

@@ -275,6 +275,10 @@ nsDisplayCanvasBackgroundColor::BuildLayer(nsDisplayListBuilder* aBuilder,
     return nullptr;
   }
 
+  if (aManager->GetBackendType() == layers::LayersBackend::LAYERS_WR) {
+    return BuildDisplayItemLayer(aBuilder, aManager, aContainerParameters);
+  }
+
   RefPtr<ColorLayer> layer = static_cast<ColorLayer*>
     (aManager->GetLayerBuilder()->GetLeafLayerFor(aBuilder, this));
   if (!layer) {
@@ -298,6 +302,27 @@ nsDisplayCanvasBackgroundColor::BuildLayer(nsDisplayListBuilder* aBuilder,
   return layer.forget();
 }
 
+void
+nsDisplayCanvasBackgroundColor::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
+                                                        nsTArray<WebRenderParentCommand>& aParentCommands,
+                                                        WebRenderDisplayItemLayer* aLayer)
+{
+  nsCanvasFrame* frame = static_cast<nsCanvasFrame*>(mFrame);
+  nsPoint offset = ToReferenceFrame();
+  nsRect bgClipRect = frame->CanvasArea() + offset;
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+
+  Rect devPxRect(Float(bgClipRect.x / appUnitsPerDevPixel),
+                 Float(bgClipRect.y / appUnitsPerDevPixel),
+                 Float(bgClipRect.width / appUnitsPerDevPixel),
+                 Float(bgClipRect.height / appUnitsPerDevPixel));
+
+  Rect transformedRect = aLayer->RelativeToParent(devPxRect);
+  aBuilder.PushRect(wr::ToWrRect(transformedRect),
+                    aBuilder.BuildClipRegion(wr::ToWrRect(transformedRect)),
+                    wr::ToWrColor(ToDeviceColor(mColor)));
+}
+
 #ifdef MOZ_DUMP_PAINTING
 void
 nsDisplayCanvasBackgroundColor::WriteDebugInfo(std::stringstream& aStream)

layout/generic/nsCanvasFrame.h

@@ -14,6 +14,7 @@
 #include "nsIScrollPositionListener.h"
 #include "nsDisplayList.h"
 #include "nsIAnonymousContentCreator.h"
+#include "gfxPrefs.h"
 
 class nsPresContext;
 class nsRenderingContext;
@@ -161,19 +162,22 @@ public:
     // We need to override so we don't consider border-radius.
     aOutFrames->AppendElement(mFrame);
   }
+  virtual already_AddRefed<Layer> BuildLayer(nsDisplayListBuilder* aBuilder,
+                                             LayerManager* aManager,
+                                             const ContainerLayerParameters& aContainerParameters) override;
+  virtual void CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
+                                       nsTArray<WebRenderParentCommand>& aParentCommands,
+                                       mozilla::layers::WebRenderDisplayItemLayer* aLayer) override;
 
   virtual LayerState GetLayerState(nsDisplayListBuilder* aBuilder,
                                    LayerManager* aManager,
                                    const ContainerLayerParameters& aParameters) override
   {
-    if (ForceActiveLayers()) {
+    if (ForceActiveLayers() || gfxPrefs::LayersAllowCanvasBackgroundColorLayers()) {
       return mozilla::LAYER_ACTIVE;
     }
     return mozilla::LAYER_NONE;
   }
-  virtual already_AddRefed<Layer> BuildLayer(nsDisplayListBuilder* aBuilder,
-                                             LayerManager* aManager,
-                                             const ContainerLayerParameters& aContainerParameters) override;
   virtual void Paint(nsDisplayListBuilder* aBuilder,
                      nsRenderingContext* aCtx) override;