Add ability to extract YUV planes from SkImage

src/utils/SkRGBAToYUV.cpp

Index: src/utils/SkRGBAToYUV.cpp
diff --git a/src/utils/SkRGBAToYUV.cpp b/src/utils/SkRGBAToYUV.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b7f78bac14c08cc8110b0ca2935156d77b7ca2a1
--- /dev/null
+++ b/src/utils/SkRGBAToYUV.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkRGBAToYUV.h"
+#include "SkCanvas.h"
+#include "SkColorMatrixFilterRowMajor255.h"
+#include "SkImage.h"
+#include "SkPaint.h"
+#include "SkSurface.h"
+
+bool SkRGBAToYUV(const SkImage* image, const SkISize sizes[3], void* const planes[3],
+                 const size_t rowBytes[3], SkYUVColorSpace colorSpace) {
+    // Matrices that go from RGBA to YUV.
+    static const SkScalar kYUVColorSpaceInvMatrices[][15] = {
+        // kJPEG_SkYUVColorSpace
+        { 0.299001f,  0.586998f,   0.114001f,  0.f, 0.0000821798f * 255.f,
+         -0.168736f, -0.331263f,   0.499999f,  0.f, 0.499954f * 255.f,
+          0.499999f, -0.418686f,  -0.0813131f, 0.f, 0.499941f * 255.f},
+
+        // kRec601_SkYUVColorSpace
+        { 0.256951f,  0.504421f,   0.0977346f, 0.f, 0.0625f * 255.f,
+         -0.148212f, -0.290954f,   0.439166f,  0.f, 0.5f * 255.f,
+          0.439166f,  -0.367886f, -0.0712802f, 0.f, 0.5f * 255.f},
+
+        // kRec709_SkYUVColorSpace
+        { 0.182663f,  0.614473f,  0.061971f,  0.f, 0.0625f * 255.f,
+         -0.100672f, -0.338658f,  0.43933f,   0.f, 0.5f * 255.f,
+          0.439142f, -0.39891f,  -0.040231f,  0.f, 0.5f * 255.f},
+    };
+    static_assert(kLastEnum_SkYUVColorSpace == 2, "yuv color matrix array problem");
+    static_assert(kJPEG_SkYUVColorSpace     == 0, "yuv color matrix array problem");
+    static_assert(kRec601_SkYUVColorSpace   == 1, "yuv color matrix array problem");
+    static_assert(kRec709_SkYUVColorSpace   == 2, "yuv color matrix array problem");
+
+    for (int i = 0; i < 3; ++i) {
+        size_t rb = rowBytes[i] ? rowBytes[i] : sizes[i].fWidth;
+        SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterDirect(
+                SkImageInfo::MakeA8(sizes[i].fWidth, sizes[i].fHeight), planes[i], rb));
+        if (!surface) {
+            return false;
+        }
+        SkPaint paint;
+        paint.setFilterQuality(kLow_SkFilterQuality);
+        paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+        int rowStartIdx = 5 * i;
+        const SkScalar* row = kYUVColorSpaceInvMatrices[colorSpace] + rowStartIdx;
+        paint.setColorFilter(
+                SkColorMatrixFilterRowMajor255::CreateSingleChannelOutput(row))->unref();
+        surface->getCanvas()->drawImageRect(image, SkIRect::MakeWH(image->width(), image->height()),
+                                            SkRect::MakeIWH(surface->width(), surface->height()),
+                                            &paint);
+    }
+    return true;
+}