Provides multiple implementations of Android's SkBitmapRegionDecoder

src/utils/SkBitmapRegionDecoder.h

Index: src/utils/SkBitmapRegionDecoder.h
diff --git a/src/utils/SkBitmapRegionDecoder.h b/src/utils/SkBitmapRegionDecoder.h
new file mode 100644
index 0000000000000000000000000000000000000000..91dd5625a566fd22d482a5dfadba886a8b737071
--- /dev/null
+++ b/src/utils/SkBitmapRegionDecoder.h
@@ -0,0 +1,77 @@
+/*
+ * 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 SkBitmapRegionDecoder_DEFINED
+#define SkBitmapRegionDecoder_DEFINED
+
+#include "SkBitmap.h"
+#include "SkStream.h"
+
+/*
+ * This class aims to provide an interface to test multiple implementations of
+ * SkBitmapRegionDecoder.
+ */
+class SkBitmapRegionDecoder {
+public:
+
+    enum Strategy {
+        kCanvas_Strategy,   // Draw to the canvas, uses SkCodec
+        kOriginal_Strategy, // Sampling, uses SkImageDecoder
+        // TODO (msarett): Add strategy for SkScaledCodec
+    };
+
+    /*
+     * @param stream   Encoded image stream, takes ownership
+     * @param strategy Strategy used for scaling and subsetting
+     * @return         Tries to create an SkBitmapRegionDecoder, returns NULL
+     *                 on failure
+     */
+    static SkBitmapRegionDecoder* CreateBitmapRegionDecoder(
+            SkStreamRewindable* stream, Strategy strategy);
+
+    /*
+     * Decode a scaled region of the encoded image stream
+     *
+     * @param start_x    X-coordinate of upper-left corner of region.

[scroggo, 2015/09/02 21:32:24]

So if I understand correctly, these can be negative?

[msarett, 2015/09/03 19:20:52]

Yes.  This is unfortunate, but it's currently allowed in Android.

+     *                   This coordinate is unscaled, relative to the original dimensions.
+     * @param start_y    Y-coordinate of upper-left corner of region.
+     *                   This coordinate is unscaled, relative to the original dimensions.
+     * @param width      Width of the region to decode.
+     *                   This distance is unscaled, relative to the original dimensions.
+     * @param height     Height of the region to decode.
+     *                   This distance is unscaled, relative to the original dimensions.
+     * @param sampleSize An integer downscaling factor for the decode.
+     * @param colorType  Preferred output colorType.
+     *                   New implementations should return NULL if they do not support
+     *                   decoding to this color type.
+     *                   The old kOriginal_Strategy will decode to a default color type
+     *                   if this color type is unsupported.
+     * @return           Pointer to a bitmap of the decoded region on success, NULL on
+     *                   failure.
+     */
+    virtual SkBitmap* decodeRegion(int start_x, int start_y, int width,
+                                   int height, int sampleSize,
+                                   SkColorType colorType) = 0;
+
+    int width() const { return fWidth; }
+    int height() const { return fHeight; }
+
+    virtual ~SkBitmapRegionDecoder() {}
+
+protected:
+
+    SkBitmapRegionDecoder(int width, int height)
+        : fWidth(width)
+        , fHeight(height)
+    {}
+
+private:
+    const int fWidth;
+    const int fHeight;
+};
+
+#endif