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

[Dave Airlie]

On 14 June 2016 at 16:11, Dave Airlie <airlied at gmail.com> wrote:
> 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.

https://cgit.freedesktop.org/~airlied/virglrenderer/commit/?h=fix-red-blit-shader&id=20916f13f66e10705a8220e78daac3862fb8db5d

seems to work for me.

Dave.