[Mesa-dev] [RFC PATCH] arb_texture_barrier: call glTextureBarrier after each glDrawRangeElements

[Nicolai Hähnle]

Hi Alejandro,

my understanding of the spec is that the test should be correct as 
originally written, i.e. with glTextureBarrier only between full 
rectangle draws.

FWIW, radeonsi passes the test as-is (though I reduced the GLSL version 
requirement, which I'd ask you to change as well before you push the test).

Cheers,
Nicolai

On 24.06.2016 11:14, Alejandro Piñeiro wrote:
> Gets the test passing for cases with low resolution, high amount
> of triangles and more than one glDrawRangeElements (drawing_passes).
> ---
>
> Just to catch attention, this issue also affects the failing CTS test
> GL44-CTS.texture_barrier_ARB.same-texel-rw-multipass on Intel gen7+.
>
> And sorry for the cross-posting, but usually questions related about
> specs are more suited for mesa-dev.
>
> The test I have just sent to piglit list fails in the following scenario:
>    * Low resolution
>    * High amount of triangles on the square draw
>    * More than one glDrawRangeElements to render the square.
>
> As this patch shows, the problem gets solved if I move the
> glTextureBarrier call just after glDrawRangeElements, instead of
> having it after each full square drawn.
>
> But Im not sure if this should be needed if we strictly follow the
> spec. The spec [1] even include a example of when the barrier would
> not be needed on Issue 1. If what you are drawing doesn't intersect to
> what you have been drawing before, you don't need to call
> glTextureBarrier. Being strict, the test is drawing non intersecting
> elements, as the triangles are independent one from the other. But it
> is also true that this is somewhat debatable as the borders of the
> triangles are shared, so with low resolution and a high amount of
> triangles it can cause these artifacts.
>
> So, opinions? Is this patch correct so the problem was on the piglit
> test? Or this patch should not be needed so the problem is on the
> implementation of arb_texture_barrier?
>
> [1] https://www.opengl.org/registry/specs/ARB/texture_barrier.txt
>
>   tests/spec/arb_texture_barrier/blending-in-shader-arb.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/tests/spec/arb_texture_barrier/blending-in-shader-arb.c b/tests/spec/arb_texture_barrier/blending-in-shader-arb.c
> index 76822da..c84cfaf 100644
> --- a/tests/spec/arb_texture_barrier/blending-in-shader-arb.c
> +++ b/tests/spec/arb_texture_barrier/blending-in-shader-arb.c
> @@ -318,6 +318,7 @@ draw_rect_tex()
>
>                   glDrawRangeElements(GL_TRIANGLES, first, first + count, count,
>                                       GL_UNSIGNED_INT, BUFFER_OFFSET(first * sizeof(GLuint)));
> +                glTextureBarrier();
>                   first += count;
>           }
>   }
> @@ -330,8 +331,6 @@ piglit_display(void)
>           glViewport(0, 0, width, height);
>
>           for (i = 0; i < blend_passes; i++) {
> -                if (i != 0)
> -                        glTextureBarrier();
>                   draw_rect_tex();
>           }
>
>