[Mesa-dev] EXT_shader_image_load_store requires format-less loads?

[Ilia Mirkin]

Hi Pierre-Eric,

I see you recently added EXT_shader_image_load_store - nice. It seems
like you're relying on the format-less read access feature to make it
happen:

+   extensions->EXT_shader_image_load_store &=
+      screen->get_param(screen, PIPE_CAP_IMAGE_LOAD_FORMATTED);

Can you elaborate why this is necessary? From a quick read of the
spec, it seems like the format is required, and maps to a format same
way that ARB_image_load_store does (well, *slightly* different, but in
the end, we get one of those same enum values out). The LOAD_FORMATTED
thing enables you to read from an image with PIPE_FORMAT_NONE (which
normally can only be written to).

I don't see anything in the spec which requires it, but perhaps I
missed something. I'd be a bit surprised though, since this is rather
non-trivial on NVIDIA GPUs.

Cheers,

  -ilia