[Piglit] problem with msaa dual source blending tests

[Anuj Phogat]

On Wed, Aug 22, 2012 at 12:48 AM, Vadim Girlin <vadimgirlin at gmail.com> wrote:
> Hi,
>
> It seems there is a problem with alpha-to-coverage-dual-src-blend test.
>
> AFAICS the test uses DrawPixels with dual source blending and
> fixed-function fragment pipeline. According to GL and
> ARB_blend_func_extended specs:
>
> "Rendering using any of the blend functions that consume the second
> input color (SRC1_COLOR, ONE_MINUS_SRC1_COLOR, SRC1_ALPHA or
> ONE_MINUS_SRC1_ALPHA) using fixed function will produce undefined
> results."
>
> So it looks like the test relies on the undefined behaviour. Here is the
> part of the stack for that DrawPixels call:
>
>         12 visualize_image() common.cpp:1775
>         11 draw_image_to_window_system_fb() draw-buffers-common.cpp:704
>         10 draw_reference_image() draw-buffers-common.cpp:823
>         9  piglit_display() alpha-to-coverage-dual-src-blend.cpp:104
>
> Probably blending should be temporarily disabled in that case.
Yes. Blending can be temporarily disabled in visualize_image function.
I'll send out a small patch to fix this. Patch won't make any difference
to the test output. Test is already passing on AMD, Intel and NVIDIA drivers.
Thanks for noticing this.

>
> Vadim
>