If the state tracker chooses to implement one format with a more
general one (e.g. GL_ALPHA implemented with GL_RGBA) we end up
in a situation where some components should be ignored. Readpix
handles this correctly, but blit does not, which means that if
we blit between different formats we can end up writing garbage
into some components. Work around this by adding an explicit
swizzle to the pipe_blit_info struct, which can re-arrange elements
and/or put 0 or 1 into appropriate channels, and use this to
set the appropriate values into unused channels via the sampler
view.
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31378>
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