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Recheck the animated canvas calculation logic, fix the issue of that calculation #23

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Merged
merged 1 commit into from
Sep 12, 2019
Merged

Recheck the animated canvas calculation logic, fix the issue of that calculation #23

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13 changes: 8 additions & 5 deletions SDWebImageWebPCoder/Classes/SDImageWebPCoder.m
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Original file line number Diff line number Diff line change
Expand Up @@ -810,12 +810,10 @@ - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
// But when one frame's dispose method is `WEBP_MUX_DISPOSE_BACKGROUND`, the canvas is cleared after the frame decoded. And subsequent frames are not effected by that frame.
// So, we calculate each frame's `blendFromIndex`. Then directly draw canvas from that index, instead of always from 0 index.

if (_currentBlendIndex + 1 == index) {
if (_currentBlendIndex != NSNotFound && _currentBlendIndex + 1 == index) {
// If the request index is subsequence of current blend index, it does not matter what dispose method is. The canvas is always ready.
_currentBlendIndex = index;
NSUInteger startIndex = index;
// libwebp's index start with 1
if (!WebPDemuxGetFrame(_demux, (int)(startIndex + 1), &iter)) {
if (!WebPDemuxGetFrame(_demux, (int)(index + 1), &iter)) {
WebPDemuxReleaseIterator(&iter);
return nil;
}
Expand All @@ -824,7 +822,6 @@ - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
if (_currentBlendIndex != NSNotFound) {
CGContextClearRect(_canvas, CGRectMake(0, 0, _canvasWidth, _canvasHeight));
}
_currentBlendIndex = index;

// Then, loop from the blend from index, draw each of previous frames on the canvas.
// We use do while loop to call `WebPDemuxNextFrame`(fast), until the endIndex meet.
Expand All @@ -843,7 +840,13 @@ - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
}
} while ((size_t)iter.frame_num < endIndex && WebPDemuxNextFrame(&iter));
}
// libwebp's index start with 1
if (!WebPDemuxGetFrame(_demux, (int)(index + 1), &iter)) {
WebPDemuxReleaseIterator(&iter);
return nil;
}
}
_currentBlendIndex = index;

// Now the canvas is ready, which respects of dispose method behavior. Just do normal decoding and produce image.
CGImageRef imageRef = [self sd_drawnWebpImageWithCanvas:_canvas iterator:iter colorSpace:_colorSpace];
Expand Down