Discard atlas after every MultiPictureDraw::draw

src/gpu/GrLayerCache.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrLayerCache_DEFINED
 #define GrLayerCache_DEFINED
 
 #include "GrAtlas.h"
 #include "GrPictureUtils.h"
 #include "GrRect.h"
 
 #include "SkChecksum.h"
 #include "SkMessageBus.h"
 #include "SkTDynamicHash.h"
 
 class SkPicture;
 
+// Set to 0 to disable caching of hoisted layers
+#define GR_CACHE_HOISTED_LAYERS 0
+
 // The layer cache listens for these messages to purge picture-related resources.
 struct GrPictureDeletedMessage {
     uint32_t pictureID;
 };
 
 // GrPictureInfo stores the atlas plots used by a single picture. A single 
 // plot may be used to store layers from multiple pictures.
 struct GrPictureInfo {
 public:
     // for SkTDynamicHash - just use the pictureID as the hash key
@@ skipping 211 matching lines @@
     SkDEBUGCODE(void validate() const;)
 
 #ifdef SK_DEVELOPER
     void writeLayersToDisk(const SkString& dirName);
 #endif
 
     static bool PlausiblyAtlasable(int width, int height) {
         return width <= kPlotWidth && height <= kPlotHeight;
     }
 
+#if !GR_CACHE_HOISTED_LAYERS
+    void purgeAll();
+#endif
+
 private:
     static const int kAtlasTextureWidth = 1024;
     static const int kAtlasTextureHeight = 1024;
 
     static const int kNumPlotsX = 2;
     static const int kNumPlotsY = 2;
 
     static const int kPlotWidth = kAtlasTextureWidth / kNumPlotsX;
     static const int kPlotHeight = kAtlasTextureHeight / kNumPlotsY;
 
@@ skipping 22 matching lines @@
     int fPlotLocks[kNumPlotsX * kNumPlotsY];
 
     // Inform the cache that layer's cached image is not currently required
     void unlock(GrCachedLayer* layer);
 
     void initAtlas();
     GrCachedLayer* createLayer(uint32_t pictureID, int start, int stop, 
                                const SkIRect& bounds, const SkMatrix& ctm, 
                                const SkPaint* paint);
 
-    void purgeAll();
-
     // Remove all the layers (and unlock any resources) associated with 'pictureID'
     void purge(uint32_t pictureID);
 
     void purgePlot(GrPlot* plot);
 
     // Try to find a purgeable plot and clear it out. Return true if a plot
     // was purged; false otherwise.
     bool purgePlot();
 
     void incPlotLock(int plotIdx) { ++fPlotLocks[plotIdx]; }
     void decPlotLock(int plotIdx) {
         SkASSERT(fPlotLocks[plotIdx] > 0);
         --fPlotLocks[plotIdx];
     }
 
     // for testing
     friend class TestingAccess;
     int numLayers() const { return fLayerHash.count(); }
 };
 
 #endif