Provides multiple implementations of Android's SkBitmapRegionDecoder

tools/SkBitmapRegionSampler.cpp

+/*
+ * 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 "SkBitmapRegionSampler.h"
+
+SkBitmapRegionSampler::SkBitmapRegionSampler(SkImageDecoder* decoder, int width, 
+                                             int height)
+    : INHERITED(width, height)
+    , fDecoder(decoder)
+{}
+
+/*
+ * Three differences from the Android version:
+ *     Returns a Skia bitmap instead of an Android bitmap.
+ *     Android version attempts to reuse a recycled bitmap.
+ *     Removed the options object and used parameters for color type and
+ *     sample size.
+ */
+SkBitmap* SkBitmapRegionSampler::decodeRegion(int start_x, int start_y,
+                                              int width, int height,
+                                              int sampleSize,
+                                              SkColorType prefColorType) {
+    // Match Android's default settings
+    fDecoder->setDitherImage(true);
+    fDecoder->setPreferQualityOverSpeed(false);
+    fDecoder->setRequireUnpremultipliedColors(false);
+    fDecoder->setSampleSize(sampleSize);
+
+    // kAlpha8 is the legacy representation of kGray8 used by SkImageDecoder
+    if (kGray_8_SkColorType == prefColorType) {
+        prefColorType = kAlpha_8_SkColorType;
+    }
+
+    SkIRect region;
+    region.fLeft = start_x;
+    region.fTop = start_y;
+    region.fRight = start_x + width;
+    region.fBottom = start_y + height;
+
+    SkAutoTDelete<SkBitmap> bitmap(new SkBitmap());
+    if (!fDecoder->decodeSubset(bitmap.get(), region, prefColorType)) {
+        SkDebugf("Error: decodeRegion failed.\n");
+        return nullptr;
+    }
+    return bitmap.detach();
+}