[virglrenderer-devel] regarding ARGB_copy_image and 3 component textures

[Gert Wollny]

Dear all, 

I'm running into a dead end trying to get three componet textures to
behave with the copy_image tests (both piglit and dEQP-GLES31). 

The problems that I initially encountered were that on an Intel host a
RBG32F texture would be represented by 128 bit per texel (as RGBA32F)
in a way visible to the host and the RGB32UI and RGB32I textures were
still in 96 bits. As a result an assertion in gallium copy_image fired,
because only textures with the same texel bit count can be copied. 

In a similar way, on the R600 host copying between sRGB and RGB failed,
because the latter was represented as a four component texture, but the
sRGB texture not, and virglrenderer directed the blit to use
framebuffer blits which failed because of the gamma correction
involved.

Given that two different hosts showed different problems I thought that
solving this is probably best done by forcing to use four component
textures with a one-swizzle in the alpha channel. This actually seemed
to work out well, but now I had to realize that this also removed 
GL_ARB_texture_buffer_object_rgb32 from the list of supported
extensions.  

I still think that the four-component approach is a possible solution,
but I'm not sure about how to keep the extension. Any ideas?

Many thanks, 
Gert