Add CTM to the cached layers' key and reduce render target pingponging in layer pre-rendering

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
 
@@ skipping 26 matching lines @@
 
     GrAtlas::ClientPlotUsage  fPlotUsage;
 };
 
 // GrCachedLayer encapsulates the caching information for a single saveLayer.
 //
 // Atlased layers get a ref to the backing GrTexture while non-atlased layers
 // get a ref to the GrTexture in which they reside. In both cases 'fRect' 
 // contains the layer's extent in its texture.
 // Atlased layers also get a pointer to the plot in which they reside.
-// For non-atlased layers the lock field just corresponds to locking in
-// the resource cache. For atlased layers it implements an additional level
+// For non-atlased layers, the lock field just corresponds to locking in
+// the resource cache. For atlased layers, it implements an additional level
 // of locking to allow atlased layers to be reused multiple times.
 struct GrCachedLayer {
 public:
     // For SkTDynamicHash
     struct Key {
-        Key(uint32_t pictureID, int layerID) : fPictureID(pictureID) , fLayerID(layerID) {}
+        Key(uint32_t pictureID, int start, int stop, const SkMatrix& ctm) 
+        : fPictureID(pictureID)
+        , fStart(start)
+        , fStop(stop)
+        , fCTM(ctm) {
+            fCTM.getType(); // force initialization of type so hashes match
+
+            // Key needs to be tightly packed.
+            GR_STATIC_ASSERT(sizeof(Key) == sizeof(uint32_t) + 2 * sizeof(int) + 
+                                            9 * sizeof(SkScalar) + sizeof(uint32_t));
+        }
 
         bool operator==(const Key& other) const {
-            return fPictureID == other.fPictureID && fLayerID == other.fLayerID;
+            return fPictureID == other.fPictureID &&
+                   fStart == other.fStart &&
+                   fStop == other.fStop &&
+                   fCTM.cheapEqualTo(other.fCTM);
         }
 
-        uint32_t getPictureID() const { return fPictureID; }
-        int      getLayerID() const { return fLayerID; }
+        uint32_t pictureID() const { return fPictureID; }
+        int start() const { return fStart; }
+        int stop() const { return fStop; }
+        const SkMatrix& ctm() const { return fCTM; }
 
     private:
         // ID of the picture of which this layer is a part
         const uint32_t fPictureID;
-        // fLayerID is the index of this layer in the picture (one of 0 .. #layers).
-        const int      fLayerID;
+        // The range of commands in the picture this layer represents
+        const int      fStart;
+        const int      fStop;
+        // The CTM applied to this layer in the picture
+        SkMatrix       fCTM;
     };
 
     static const Key& GetKey(const GrCachedLayer& layer) { return layer.fKey; }
     static uint32_t Hash(const Key& key) { 
-        return SkChecksum::Mix((key.getPictureID() << 16) | key.getLayerID());
+        return SkChecksum::Murmur3(reinterpret_cast<const uint32_t*>(&key), sizeof(Key));
     }
 
     // GrCachedLayer proper
-    GrCachedLayer(uint32_t pictureID, int layerID) 
-        : fKey(pictureID, layerID)
+    GrCachedLayer(uint32_t pictureID, int start, int stop, const SkMatrix& ctm) 
+        : fKey(pictureID, start, stop, ctm)
         , fTexture(NULL)
         , fRect(GrIRect16::MakeEmpty())
         , fPlot(NULL)
         , fLocked(false) {
-        SkASSERT(SK_InvalidGenID != pictureID && layerID >= 0);
+        SkASSERT(SK_InvalidGenID != pictureID && start >= 0 && stop >= 0);
     }
 
     ~GrCachedLayer() {
         SkSafeUnref(fTexture);
     }
 
-    uint32_t pictureID() const { return fKey.getPictureID(); }
-    int layerID() const { return fKey.getLayerID(); }
+    uint32_t pictureID() const { return fKey.pictureID(); }
+    int start() const { return fKey.start(); }
+    int stop() const { return fKey.stop(); }
+    const SkMatrix& ctm() const { return fKey.ctm(); }
 
     void setTexture(GrTexture* texture, const GrIRect16& rect) {
         SkRefCnt_SafeAssign(fTexture, texture);
         fRect = rect;
     }
     GrTexture* texture() { return fTexture; }
     const GrIRect16& rect() const { return fRect; }
 
     void setPlot(GrPlot* plot) {
         SkASSERT(NULL == fPlot);
@@ skipping 43 matching lines @@
 // classes.
 class GrLayerCache {
 public:
     GrLayerCache(GrContext*);
     ~GrLayerCache();
 
     // As a cache, the GrLayerCache can be ordered to free up all its cached
     // elements by the GrContext
     void freeAll();
 
-    GrCachedLayer* findLayer(const SkPicture* picture, int layerID);
-    GrCachedLayer* findLayerOrCreate(const SkPicture* picture, int layerID);
+    GrCachedLayer* findLayer(const SkPicture* picture, int start, int stop, const SkMatrix& ctm);
+    GrCachedLayer* findLayerOrCreate(const SkPicture* picture, 
+                                     int start, int stop, 
+                                     const SkMatrix& ctm);
     
     // Inform the cache that layer's cached image is now required. Return true
     // if it was found in the ResourceCache and doesn't need to be regenerated.
     // If false is returned the caller should (re)render the layer into the
     // newly acquired texture.
     bool lock(GrCachedLayer* layer, const GrTextureDesc& desc);
 
     // Inform the cache that layer's cached image is not currently required
     void unlock(GrCachedLayer* layer);
 
@@ skipping 33 matching lines @@
 
     // This implements a plot-centric locking mechanism (since the atlas
     // backing texture is always locked). Each layer that is locked (i.e.,
     // needed for the current rendering) in a plot increments the plot lock
     // count for that plot. Similarly, once a rendering is complete all the
     // layers used in it decrement the lock count for the used plots.
     // Plots with a 0 lock count are open for recycling/purging.
     int fPlotLocks[kNumPlotsX * kNumPlotsY];
 
     void initAtlas();
-    GrCachedLayer* createLayer(const SkPicture* picture, int layerID);
+    GrCachedLayer* createLayer(const SkPicture* picture, int start, int stop, const SkMatrix& ctm);
 
     // Remove all the layers (and unlock any resources) associated with 'pictureID'
     void purge(uint32_t pictureID);
 
     static bool PlausiblyAtlasable(int width, int height) {
         return width <= kPlotWidth && height <= kPlotHeight;
     }
 
     // Try to find a purgeable plot and clear it out. Return true if a plot
     // was purged; false otherwise.
     bool purgePlot();
 
     // for testing
     friend class TestingAccess;
     int numLayers() const { return fLayerHash.count(); }
 };
 
 #endif