[virglrenderer-devel] [PATCH 4/4] blit: fix blitting to red-alpha texture

[Dave Airlie]

On 11 June 2016 at 03:25,  <marcandre.lureau at redhat.com> wrote:
> From: Marc-André Lureau <marcandre.lureau at redhat.com>
>
> glBlitFramebuffer() doesn't take swizzling into account, so use
> blit_gl() fallback in this case with a alpha->red swizzle.
>
> This fixes text rendering with Qt
> QGLTextureGlyphCache::resizeTextureData(), as can be reproduced with
> stellarium or qt5/examples/widgets/graphicsview/chip/chip.

I like the GLX workarounds, so I'll take those, as apitrace is a pita
with epoxy. I've
hacked it locally a few times but it's always messy.

However I don't think this fix is fully correct,

What we are doing here is if the destination is ALPHA we are taking the ALPHA
channel from the source into RED, we should be adjusting the shader I
think in this
case to write the alpha not the red.

If the source was ALPHA we should be using the swizzle. Granted there might
not be a difference in the end result.

https://cgit.freedesktop.org/~airlied/virglrenderer/commit/?h=fix-red-blit&id=b50aaa0396256e68e784ae57eac4c408701719e3
was my alternate patch that does the same thing as yours without
redoing all the swizzle code.

However I think we need to look at changing the shader when the dst is
emulated alpha.

Dave.