picdocument: fix rendering of animated GIFs #653
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pic.lua was returning each frame as-is. Very often, frames are just a mask to apply on previous frame, so we need to combine them and paste each one over the previous. Adds support for transparency for that, and limited support for the rare other "dispose" modes of the GIF spec.
Frenzie
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Apr 19, 2018
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Apr 20, 2018
Includes: * picdocument: fix rendering of animated GIFs koreader/koreader-base#653 * [build] Some minor build tweaks koreader/koreader-base#651 * [chore, CI] Update to latest Docker images koreader/koreader-base#654 * [chore, Kobo] Deprecate Kobo always UTF8Filename() patch koreader/koreader-base#655 (upstream integrated workaround for koreader#542 previous fix in koreader#3845)
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pic.lua was returning each frame as-is. Very often, frames are just a mask to apply on previous frame, so we need to combine them and paste each one over the previous.
Adds support for transparency for that, and limited support for the rare other "dispose" modes of the GIF spec.
This makes the little (or full size) animated territories expansion maps (gray backround with a year displayed) found on these Wikipedia pages, when saved as a GIF, correctly displayed by PicDocument:
https://fr.wikipedia.org/wiki/Empire_romain https://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Roman_Republic_Empire_map.gif/220px-Roman_Republic_Empire_map.gif
https://fr.wikipedia.org/wiki/Saint-Empire_romain_germanique https://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/HRR.gif/220px-HRR.gif
https://fr.wikipedia.org/wiki/Empire_byzantin https://upload.wikimedia.org/wikipedia/commons/thumb/4/40/Byzantine_Empire_animated.gif/220px-Byzantine_Empire_animated.gif
(Needs to clear cache if comparing previous/after.)
I was thinking about adding support for such animated GIF in ImageViewer (so we can view them from Wikipedia saved as EPUB), but I first had to see how they work. MuPDF (used to render images) has no support for multi-frames images. Had to have a look a ffi/pic.lua which uses giflib, that does have support for them. So I just fixed the handling of these animated gif in pic.lua, even if I guess hardly nobody uses that feature.