Nico Weber b7e31ba194 WebP/Lossy: Add test for lossy webp with uncompressed alpha ...

The alpha channel of a lossy webp is always stored separately from
the (lossy) RGB data. Alpha is either compressed in a lossless webp
that stores just the alpha data, or it's stored completely
uncompressed. (But again, even if it's compressed, it's losslessly
compressed.)

This adds a test for uncompressed alpha, which I hadn't tested before.
It seems to work correctly, though :^)

I generated the test image by running:

    ~/Downloads/libwebp-1.3.0-mac-arm64/bin/cwebp \
      -alpha_method 0 \
      Tests/LibGfx/test-inputs/extended-lossless.webp \
      -o Tests/LibGfx/test-inputs/extended-lossy-uncompressed-alpha.webp

2023-05-30 06:14:56 +02:00

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