Bug 854873. Keep scissor rect enabled. r=kats,nical

gfx/layers/Compositor.h

@@ -399,6 +399,12 @@ public:
   virtual nsIWidget* GetWidget() const { return nullptr; }
   virtual const nsIntSize& GetWidgetSize() = 0;
 
+  // Call before and after any rendering not done by this compositor but which
+  // might affect the compositor's internal state or the state of any APIs it
+  // uses. For example, internal GL state.
+  virtual void SaveState() {}
+  virtual void RestoreState() {}
+
   /**
    * Debug-build assertion that can be called to ensure code is running on the
    * compositor thread.

gfx/layers/composite/LayerManagerComposite.cpp

@@ -348,19 +348,23 @@ LayerManagerComposite::Render()
   }
 
   // Allow widget to render a custom background.
+  mCompositor->SaveState();
   mCompositor->GetWidget()->DrawWindowUnderlay(this, nsIntRect(actualBounds.x,
                                                                actualBounds.y,
                                                                actualBounds.width,
                                                                actualBounds.height));
+  mCompositor->RestoreState();
 
   // Render our layers.
   RootLayer()->RenderLayer(nsIntPoint(0, 0), clipRect);
 
   // Allow widget to render a custom foreground.
+  mCompositor->SaveState();
   mCompositor->GetWidget()->DrawWindowOverlay(this, nsIntRect(actualBounds.x,
                                                               actualBounds.y,
                                                               actualBounds.width,
                                                               actualBounds.height));
+  mCompositor->RestoreState();
 
   // Debugging
   RenderDebugOverlay(actualBounds);

gfx/layers/opengl/CompositorOGL.cpp

@@ -510,7 +510,7 @@ CompositorOGL::Initialize()
   if (console) {
     nsString msg;
     msg +=
-      NS_LITERAL_STRING("OpenGL LayerManager Initialized Succesfully.\nVersion: ");
+      NS_LITERAL_STRING("OpenGL compositor Initialized Succesfully.\nVersion: ");
     msg += NS_ConvertUTF8toUTF16(
       nsDependentCString((const char*)mGLContext->fGetString(LOCAL_GL_VERSION)));
     msg += NS_LITERAL_STRING("\nVendor: ");
@@ -817,6 +817,8 @@ CompositorOGL::BeginFrame(const Rect *aClipRectIn, const gfxMatrix& aTransform,
                                  LOCAL_GL_ONE, LOCAL_GL_ONE);
   mGLContext->fEnable(LOCAL_GL_BLEND);
 
+  mGLContext->fEnable(LOCAL_GL_SCISSOR_TEST);
+
   if (!aClipRectIn) {
     mGLContext->fScissor(0, 0, width, height);
     if (aClipRectOut) {
@@ -826,8 +828,6 @@ CompositorOGL::BeginFrame(const Rect *aClipRectIn, const gfxMatrix& aTransform,
     mGLContext->fScissor(aClipRectIn->x, aClipRectIn->y, aClipRectIn->width, aClipRectIn->height);
   }
 
-  mGLContext->fEnable(LOCAL_GL_SCISSOR_TEST);
-
   // If the Android compositor is being used, this clear will be done in
   // DrawWindowUnderlay. Make sure the bits used here match up with those used
   // in mobile/android/base/gfx/LayerRenderer.java
@@ -986,8 +986,12 @@ CompositorOGL::DrawQuad(const Rect& aRect, const Rect& aClipRect,
   PROFILER_LABEL("CompositorOGL", "DrawQuad");
   MOZ_ASSERT(mFrameInProgress, "frame not started");
 
+  Rect clipRect = aClipRect;
+  if (!mTarget) {
+    clipRect.MoveBy(mRenderOffset.x, mRenderOffset.y);
+  }
   IntRect intClipRect;
-  aClipRect.ToIntRect(&intClipRect);
+  clipRect.ToIntRect(&intClipRect);
   mGLContext->PushScissorRect(nsIntRect(intClipRect.x, intClipRect.y,
                                         intClipRect.width, intClipRect.height));
 
@@ -1441,6 +1445,21 @@ CompositorOGL::GetMaxTextureSize() const
   return texSize;
 }
 
+void
+CompositorOGL::SaveState()
+{
+  mGLContext->PushScissorRect();
+}
+
+void
+CompositorOGL::RestoreState()
+{
+  // Restore state that might be changed by drawBackground/drawForeground in
+  // mobile/android/base/gfx/LayerRenderer.java
+  mGLContext->fEnable(LOCAL_GL_SCISSOR_TEST);
+  mGLContext->PopScissorRect();
+}
+
 void
 CompositorOGL::MakeCurrent(MakeCurrentFlags aFlags) {
   if (mDestroyed) {

gfx/layers/opengl/CompositorOGL.h

@@ -158,6 +158,9 @@ public:
     return gfx::FORMAT_R8G8B8A8;
   }
 
+  virtual void SaveState() MOZ_OVERRIDE;
+  virtual void RestoreState() MOZ_OVERRIDE;
+
   /**
    * The compositor provides with temporary textures for use with direct
    * textruing like gralloc texture.

mobile/android/base/gfx/LayerRenderer.java

@@ -580,6 +580,9 @@ public class LayerRenderer implements Tabs.OnTabsChangedListener {
 
         /** This function is invoked via JNI; be careful when modifying signature. */
         public void drawBackground() {
+            // Any GL state which is changed here must be restored in
+            // CompositorOGL::RestoreState
+
             GLES20.glDisable(GLES20.GL_SCISSOR_TEST);
 
             // Draw the overscroll background area as a solid color
@@ -612,6 +615,9 @@ public class LayerRenderer implements Tabs.OnTabsChangedListener {
 
         /** This function is invoked via JNI; be careful when modifying signature. */
         public void drawForeground() {
+            // Any GL state which is changed here must be restored in
+            // CompositorOGL::RestoreState
+
             /* Draw any extra layers that were added (likely plugins) */
             if (mExtraLayers.size() > 0) {
                 for (Layer layer : mExtraLayers) {