Deferred image generator subsetting

src/core/SkImageCacherator.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageCacherator_DEFINED
 #define SkImageCacherator_DEFINED
 
 #include "SkImageGenerator.h"
+#include "SkMutex.h"
 #include "SkTemplates.h"
 
 class GrContext;
 class GrTextureParams;
 class GrUniqueKey;
 class SkBitmap;
 class SkImage;
 
 /*
  *  Internal class to manage caching the output of an ImageGenerator.
@@ skipping 40 matching lines @@
      */
     SkData* refEncoded(GrContext*);
 
     // Only return true if the generate has already been cached.
     bool lockAsBitmapOnlyIfAlreadyCached(SkBitmap*);
     // Call the underlying generator directly
     bool directGeneratePixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRB,
                               int srcX, int srcY);
 
 private:
-    class SharedGenerator;
+    // Ref-counted tuple(SkImageGenerator, SkMutex) which allows sharing of one generator
+    // among several cacherators.
+    class SharedGenerator final : public SkNVRefCnt<SharedGenerator> {
+    public:
+        static sk_sp<SharedGenerator> Make(SkImageGenerator* gen) {
+            return gen ? sk_sp<SharedGenerator>(new SharedGenerator(gen)) : nullptr;
+        }
+
+    private:
+        explicit SharedGenerator(SkImageGenerator* gen) : fGenerator(gen) { SkASSERT(gen); }
+
+        friend class ScopedGenerator;
+        friend class SkImageCacherator;
+
+        std::unique_ptr<SkImageGenerator> fGenerator;
+        SkMutex                           fMutex;
+    };
     class ScopedGenerator;
 
     struct Validator {
-        Validator(SkImageGenerator*, const SkIRect* subset);
-        ~Validator();
+        Validator(sk_sp<SharedGenerator>, const SkIRect* subset);
 
         operator bool() const { return fSharedGenerator.get(); }
 
         sk_sp<SharedGenerator> fSharedGenerator;
         SkImageInfo            fInfo;
         SkIPoint               fOrigin;
         uint32_t               fUniqueID;
     };
 
     SkImageCacherator(Validator*);
@@ skipping 11 matching lines @@
     const SkImageInfo      fInfo;
     const SkIPoint         fOrigin;
     const uint32_t         fUniqueID;
 
     friend class GrImageTextureMaker;
     friend class SkImage;
     friend class SkImage_Generator;
 };
 
 #endif