Fix rendering artifacts in pull-saveLayers-forward mode

src/gpu/SkGpuDevice.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGpuDevice.h"
 
 #include "effects/GrBicubicEffect.h"
@@ skipping 1979 matching lines @@
                     kSaveLayerMaxSize < info.fSize.fHeight ||
                     info.fIsNested) {
                     continue;            // this layer is unsuitable
                 }
 
                 pullForward[j] = true;
             }
         }
     } else {
         // In this case there is no BBH associated with the picture. Pre-render
-        // all the layers
-        // TODO: intersect the bounds of each layer with the clip region to
-        // reduce the number of pre-rendered layers
+        // all the layers that intersect the drawn region
         for (int j = 0; j < gpuData->numSaveLayers(); ++j) {
             const GPUAccelData::SaveLayerInfo& info = gpuData->saveLayerInfo(j);
 
+            SkIRect layerRect = SkIRect::MakeXYWH(info.fOffset.fX,
+                                                  info.fOffset.fY,
+                                                  info.fSize.fWidth,
+                                                  info.fSize.fHeight);
+
+            if (!SkIRect::Intersects(query, layerRect)) {
+                continue;
+            }
+
             // TODO: once this code is more stable unsuitable layers can
             // just be omitted during the optimization stage
             if (!info.fValid ||
                 kSaveLayerMaxSize < info.fSize.fWidth ||
                 kSaveLayerMaxSize < info.fSize.fHeight ||
                 info.fIsNested) {
                 continue;
             }
 
             pullForward[j] = true;
@@ skipping 69 matching lines @@
         GrCachedLayer* layer = fContext->getLayerCache()->findLayerOrCreate(picture, i);
 
         if (NULL != layer->getTexture()) {
             fContext->unlockScratchTexture(layer->getTexture());
             layer->setTexture(NULL);
         }
     }
 
     return true;
 }