[Webkit-unassigned] [Bug 217897] [iOS 14] Animated WebP with transparency doesn't render properly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=217897

--- Comment #8 from jzern at google.com ---
Comment on attachment 431786
  --> https://bugs.webkit.org/attachment.cgi?id=431786
Incorrect dispose to background handling

This is a simpler example of incorrect dispose to background handling. This should clear to the background in the final frame but a leftover couple of columns from frame 2 remain. Frame 3 completely covers frame 2 so it should not need to be disposed of separately. The progression of the image should be red->blue->green->blank (background color may vary based on the application, the default is white).

$ webpmux -info repro.webp 
Canvas size: 216 x 69
Features present: animation transparency
Background color : 0xFFFFFFFF  Loop Count : 1
Number of frames: 4
No.: width height alpha x_offset y_offset duration   dispose blend image_size  compression
  1:   181    41    no       32       28     1000 background    no         42    lossless
  2:   180    41    no       34       28     1000       none    no         42    lossless
  3:   182    41    no       34       28     1000 background    no         42    lossless
  4:     1     1   yes        0        0     1000       none   yes         34    lossless

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