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..baaa9ecfdf8397b87561d0a623534800e8126ebb
--- /dev/null
+++ b/src/utils/SkRGBAToYUV.cpp
@@ -0,0 +1,54 @@
+/*
+ * 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"
+
+void 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));
+        SkPaint paint;

[robertphillips, 2016/01/29 20:33:13]

Always low ?

[bsalomon, 2016/02/01 20:27:45]

I thought about having the filter quality be part of the public API. However,
our other similar conversion all just implement bilerp. The common cases all
should use bilerp. It's hard to imagine that a caller would want us to generate
MIPs or a high quality scale for this. If the caller really wants this control
they can always by draw the RGBA image to a RGBA surface with the desired filter
quality and then call readYUV8Planes.

+        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);
+    }
+}