Hello,
With the Etnaviv driver we're running into an issue: The GPU can only render *to* BGRA formats. It can however render *from* BGRA as well as RGBA textures.
I know that the OpenGL ES standard allows drivers to choose what order is most appropriate when being asked for "GL_RGBA" textures. So back when etnaviv supported only BGRA, Mesa automatically picked that and everything was okay.
However a recent patch added support for RGBA formats in etnaviv_format.c.
Now, Mesa creates a real GL_RGBA texture when this is requested. This is all and well for rendering, however for anything using FBO to render to textures this is a problem.
Qt, for example, is assuming it can attach the GL_RGBA texture to a FBO. This fails now that GL_RGBA textures are really GL_RGBA, and it doesn't handle that error to fall back to something else so rendering issues ensue.
I'm not sure how to handle this:
- The quick fix would be to revert the RGBA formats patch, but the hardware supports rendering *from* RGBA textures fine so this would be throwing away a feature.
- Another way would be to try to fix Qt to cope with this, and try e.g. GL_BGRA_EXT when it wants to render to a texture. Burdening the client code with this seems unintuitive to me.
- Another hack would be to implement shader variants, and swap R/B in the pixel shader to emulate rendering to RGBA.
Neither seems great. Does anyone have suggestions, do any of the other (gallium) drivers have this problem?
Regards, Wladimir