I accidentally skipped this part of the spec in the QOI decoder:
> The alpha value remains unchanged from the previous pixel.
This led to incorrect rendering of some images with transparency,
visible in form of a horizontal line of non-transparent pixels (that
shouldn't exist), e.g. for the following chunk sequence:
- QOI_OP_RGBA with alpha = 0
- QOI_OP_RGB
- QOI_OP_RUN
The QOI_OP_RGB should 'inherit' the alpha value of the previous
QOI_OP_RGBA chunk, instead of always setting it to 255.
I'm unsure why the encoder added the QOI_OP_RGB chunk to the specific
image where the bug was noticed in the first place - they effectively
both had fully transparent color values.
What the component which did the actual decoding is called is not
relevant for the error, and would be rather distracting once we show
decoding error messages e.g. in ImageViewer (instead of just silently
failing).
Also makes them more consistent as many already don't include it - a
mistake which is now turned into a feature :^)
The spec had its first stable release today, so I figured we should
support it as well!
As usual, by using the regular LibGfx image decoder plugin architecture,
we immediately get support for it everywhere: ImageViewer, FileManager
thumbnails, PixelPaint, and (with a small change in the subsequent
commit) even the Browser :^)
