Provides multiple implementations of Android's SkBitmapRegionDecoder

src/utils/SkBitmapRegionCanvas.h

Index: src/utils/SkBitmapRegionCanvas.h
diff --git a/src/utils/SkBitmapRegionCanvas.h b/src/utils/SkBitmapRegionCanvas.h
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index 0000000000000000000000000000000000000000..1cd3d170bfbd9222c15b4ce2fe8395073f9f642a
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+++ b/src/utils/SkBitmapRegionCanvas.h
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmap.h"
+#include "SkBitmapRegionDecoder.h"
+#include "SkScanlineDecoder.h"
+
+/*
+ * This class implements SkBitmapRegionDecoder by drawing to an SkCanvas.

[scroggo, 2015/09/01 22:05:28]

I'm not sure this captures what is interesting about this version - it does the
*scaling* by drawing to a canvas, right?

[msarett, 2015/09/02 18:02:23]

It also does some subsetting.  Since we can only decode full rows right now, it
subsets in the x-dimension and scales by drawing to an SkCanvas.

I will improve the comment.

I'm planning on adding the ability to get partial scanlines for SkScaledCodec -
when this lands, we should update this class.

+ */
+class SkBitmapRegionCanvas : public SkBitmapRegionDecoder {
+public:
+
+    /*
+     * Takes ownership of pointer to decoder
+     */
+    SkBitmapRegionCanvas(SkScanlineDecoder* decoder);
+
+    /*
+     * This has several key differences from the Android version:
+     *     Returns a Skia bitmap instead of an Android bitmap.
+     *     Android version attempts to reuse a recycled bitmap.
+     */
+    SkBitmap* decodeRegion(int start_x, int start_y, int width, int height,
+                           int sampleSize, SkColorType prefColorType) override;
+
+private:
+
+    SkAutoTDelete<SkScanlineDecoder> fDecoder;
+
+    typedef SkBitmapRegionDecoder INHERITED;
+
+};