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Unified Diff: third_party/WebKit/Source/platform/image-decoders/ImageFrame.cpp

Issue 2386453003: WIP: Implement APNG (Closed)
Patch Set: Revisit ImageFrame alpha setting. Created 4 years, 1 month ago
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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

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