Make GrLayerCache use multiple plots in its atlas

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
 
 #define USE_ATLAS 0
 
 #include "GrAllocPool.h"
 #include "GrAtlas.h"
 #include "GrTHashTable.h"
 #include "GrPictureUtils.h"
 #include "GrRect.h"
 
-class GrGpu;
 class SkPicture;
 
+// 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:
+    GrPictureInfo(uint32_t pictureID) : fPictureID(pictureID) { }
+
+    uint32_t fPictureID;
+
+    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.
-//
-// TODO: can we easily reuse the empty space in the non-atlased GrTexture's?
+// Atlased layers also get a pointer to the plot in which they reside.
 struct GrCachedLayer {
 public:
     GrCachedLayer(uint32_t pictureID, int layerID) 
-        : fAtlased(false) {
+        : fPlot(NULL) {
         fPictureID = pictureID;
         fLayerID = layerID;
         fTexture = NULL;
         fRect = GrIRect16::MakeEmpty();
     }
 
     uint32_t pictureID() const { return fPictureID; }
     int layerID() const { return fLayerID; }
 
     // This call takes over the caller's ref
     void setTexture(GrTexture* texture, const GrIRect16& rect) {
         if (NULL != fTexture) {
             fTexture->unref();
         }
 
         fTexture = texture; // just take over caller's ref
         fRect = rect;
     }
     GrTexture* texture() { return fTexture; }
     const GrIRect16& rect() const { return fRect; }
 
-    void setAtlased(bool atlased) { fAtlased = atlased; }
-    bool isAtlased() const { return fAtlased; }
+    void setPlot(GrPlot* plot) {
+        SkASSERT(NULL == fPlot);
+        fPlot = plot;
+    }
+    GrPlot* plot() { return fPlot; }
 
-    SkDEBUGCODE(void validate(GrTexture* backingTexture) const;)
+    bool isAtlased() const { return NULL != fPlot; }
+
+    SkDEBUGCODE(void validate(const GrTexture* backingTexture) const;)
 
 private:
     // ID of the picture of which this layer is a part
     uint32_t        fPictureID;
 
     // fLayerID is only valid when fPicture != kInvalidGenID in which case it
     // is the index of this layer in the picture (one of 0 .. #layers).
     int             fLayerID;
 
     // fTexture is a ref on the atlasing texture for atlased layers and a
     // ref on a GrTexture for non-atlased textures. In both cases, if this is
     // non-NULL, that means that the texture is locked in the texture cache.
     GrTexture*      fTexture;
 
-    // True if this layer is in an atlas; false otherwise.
-    bool            fAtlased;
-
     // For both atlased and non-atlased layers 'fRect' contains the  bound of
     // the layer in whichever texture it resides. It is empty when 'fTexture'
     // is NULL.
     GrIRect16       fRect;
+
+    // For atlased layers, fPlot stores the atlas plot in which the layer rests.
+    // It is always NULL for non-atlased layers.
+    GrPlot*         fPlot;
 };
 
 // The GrLayerCache caches pre-computed saveLayers for later rendering.
 // Non-atlased layers are stored in their own GrTexture while the atlased
 // layers share a single GrTexture.
 // Unlike the GrFontCache, the GrTexture atlas only has one GrAtlas (for 8888)
 // and one GrPlot (for the entire atlas). As such, the GrLayerCache
 // roughly combines the functionality of the GrFontCache and GrTextStrike
 // classes.
 class GrLayerCache {
@@ skipping 16 matching lines @@
 
     // Inform the cache that layer's cached image is not currently required
     void unlock(GrCachedLayer* layer);
 
     // Remove all the layers (and unlock any resources) associated with 'picture'
     void purge(const SkPicture* picture);
 
     SkDEBUGCODE(void validate() const;)
 
 private:
+    static const int kNumPlotsX = 2;
+    static const int kNumPlotsY = 2;
+
     GrContext*                fContext;  // pointer back to owning context
     SkAutoTDelete<GrAtlas>    fAtlas;    // TODO: could lazily allocate
-    GrAtlas::ClientPlotUsage  fPlotUsage;
+
+    // We cache this information here (rather then, say, on the owning picture)
+    // because we want to be able to clean it up as needed (e.g., if a picture
+    // is leaked and never cleans itself up we still want to be able to 
+    // remove the GrPictureInfo once its layers are purged from all the atlas
+    // plots).
+    class PictureKey;
+    GrTHashTable<GrPictureInfo, PictureKey, 7> fPictureHash;
 
     class PictureLayerKey;
     GrTHashTable<GrCachedLayer, PictureLayerKey, 7> fLayerHash;
 
     void initAtlas();
     GrCachedLayer* createLayer(const SkPicture* picture, int layerID);
 
     // for testing
     friend class GetNumLayers;
     int numLayers() const { return fLayerHash.count(); }
 };
 
 #endif