radeonsi: fix texture gather on stencil textures
At least on VI, texture gather doesn't work with a 24_8 data format, so use 8_8_8_8 and a modified swizzle instead. A bit of background: When creating a GL_STENCIL_INDEX8 texture, we select the X24S8 pipe format because we don't support stencil-only render targets properly. With mip-mapping this can lead to a setup where the tiling is incompatible with stencil texturing, and a flushed stencil texture is used. For the flushed stencil, a literal X24S8 is used because there were issues with an 8bpp DB->CB copy. Longer term, it would be good if we could get away from these workarounds, i.e. properly support an S8 format for stencil-only rendering and flushed stencil. Since stencil texturing is somewhat rare, it's not a high priority. Fixes GL45-CTS.texture_cube_map_array.sampling. Cc: 17.0 <mesa-stable@lists.freedesktop.org> Reviewed-by:Marek Olšák <marek.olsak@amd.com> Acked-by:
Edward O'Callaghan <funfunctor@folklore1984.net> (cherry picked from commit 3cd092c4)
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