Add the lazy decoder from PictureFlags to SkImageDecoder

tools/LazyDecodeBitmap.cpp

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "LazyDecodeBitmap.h"
+
+#include "PictureRenderingFlags.h"  // --deferImageDecoding is defined here.
+#include "SkBitmap.h"
+#include "SkData.h"
+#include "SkImageDecoder.h"
+#include "SkForceLinking.h"
+#include "SkLruImageCache.h"
+#include "SkPurgeableImageCache.h"
+#include "SkCommandLineFlags.h"
+
+__SK_FORCE_IMAGE_DECODER_LINKING;
+
+DEFINE_bool(useVolatileCache, false, "Use a volatile cache for deferred image decoding pixels. "
+            "Only meaningful if --deferImageDecoding is set to true and the platform has an "
+            "implementation.");
+
+SkLruImageCache gLruImageCache(1024 * 1024);
+
+namespace sk_tools {
+
+// Simple cache selector to choose between a purgeable cache for large images and the standard one
+// for smaller images.
+//
+class CacheSelector : public SkBitmapFactory::CacheSelector {
+
+public:
+    CacheSelector() {
+        fPurgeableImageCache = SkPurgeableImageCache::Create();
+    }
+
+    ~CacheSelector() {
+        SkSafeUnref(fPurgeableImageCache);
+    }
+
+    virtual SkImageCache* selectCache(const SkImage::Info& info) SK_OVERRIDE {
+        if (info.fWidth * info.fHeight > 32 * 1024 && fPurgeableImageCache != NULL) {
+            return fPurgeableImageCache;
+        }
+        return &gLruImageCache;
+    }
+private:
+    SkImageCache* fPurgeableImageCache;
+};
+
+static CacheSelector gCacheSelector;
+static SkBitmapFactory gFactory(&SkImageDecoder::DecodeMemoryToTarget);
+
+bool LazyDecodeBitmap(const void* buffer, size_t size, SkBitmap* bitmap) {
+    void* copiedBuffer = sk_malloc_throw(size);
+    memcpy(copiedBuffer, buffer, size);
+    SkAutoDataUnref data(SkData::NewFromMalloc(copiedBuffer, size));
+
+    static bool gOnce;
+    if (!gOnce) {
+        // Only use the cache selector if there is a purgeable image cache to use for large
+        // images.
+        if (FLAGS_useVolatileCache && SkAutoTUnref<SkImageCache>(
+                SkPurgeableImageCache::Create()).get() != NULL) {
+            gFactory.setCacheSelector(&gCacheSelector);
+        } else {
+            gFactory.setImageCache(&gLruImageCache);
+        }
+        gOnce = true;
+    }
+    return gFactory.installPixelRef(data, bitmap);
+}
+
+}  // namespace sk_tools