WIP: Implement APNG

third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp

Index: third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp b/third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp
index 152d0506ce717645e0cc5f4300a14f5d194740b3..3bb6a3eeb043fd889b0d85e678e2388964f883a4 100644
--- a/third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp
@@ -170,6 +170,49 @@ void ImageFrame::zeroFillFrameRect(const IntRect& rect) {
   setHasAlpha(true);
 }
 
+static uint8_t blendChannel(uint8_t src,
+                            uint8_t srcA,
+                            uint8_t dst,
+                            uint8_t dstA,
+                            unsigned scale) {
+  unsigned blendUnscaled = src * srcA + dst * dstA;
+  DCHECK(blendUnscaled < (1ULL << 32) / scale);
+  return (blendUnscaled * scale) >> 24;
+}
+
+static uint32_t blendSrcOverDstNonPremultiplied(uint32_t src, uint32_t dst) {
+  uint8_t srcA = SkGetPackedA32(src);
+  if (srcA == 0)
+    return dst;
+
+  uint8_t dstA = SkGetPackedA32(dst);
+  uint8_t dstFactorA = (dstA * SkAlpha255To256(255 - srcA)) >> 8;
+  DCHECK(srcA + dstFactorA < (1U << 8));
+  uint8_t blendA = srcA + dstFactorA;
+  unsigned scale = (1UL << 24) / blendA;
+
+  uint8_t blendR = blendChannel(SkGetPackedR32(src), srcA, SkGetPackedR32(dst),
+                                dstFactorA, scale);
+  uint8_t blendG = blendChannel(SkGetPackedG32(src), srcA, SkGetPackedG32(dst),
+                                dstFactorA, scale);
+  uint8_t blendB = blendChannel(SkGetPackedB32(src), srcA, SkGetPackedB32(dst),
+                                dstFactorA, scale);
+
+  return SkPackARGB32NoCheck(blendA, blendR, blendG, blendB);
+}
+
+void ImageFrame::blendRGBARaw(PixelData* dest,
+                              unsigned r,
+                              unsigned g,
+                              unsigned b,
+                              unsigned a) {
+  *dest = blendSrcOverDstNonPremultiplied(SkPackARGB32NoCheck(a, r, g, b), *dest);
+}
+
+void ImageFrame::blendSrcOverDstRaw(PixelData* src, PixelData dst) {
+  *src = blendSrcOverDstNonPremultiplied(*src, dst);
+}
+
 SkAlphaType ImageFrame::computeAlphaType() const {
   // If the frame is not fully loaded, there will be transparent pixels,
   // so we can't tell skia we're opaque, even for image types that logically