[Piglit] [PATCH] fs-texelFetchOffset-2D: don't assume undefined values to be solid black

[Eric Anholt]

sroland at vmware.com writes:

> From: Roland Scheidegger <sroland at vmware.com>
>
> core GL specifies out-of-bound texel fetches return undefined results,
> except in a robust context with ARB_robust_buffer_access_behavior supported
> (which is core in 4.3), in which case texel fetch will return 0 (OpenGL 4.3
> compatibility profile, page 387, subsection 11.1.3.2 Texel Fetches).
> Since the test requires neither robust context nor that extension it cannot
> assume any specific result value. In any case even returning zero is not what
> the test expected, since it wanted [0,0,0,1] instead.
> (With this change softpipe passes the test, as it clamps the coords.)
>
> v2: fix black->undefined, formatting, comments
> ---
>  .../glsl-1.30/execution/fs-texelFetchOffset-2D.c   |   13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/tests/spec/glsl-1.30/execution/fs-texelFetchOffset-2D.c b/tests/spec/glsl-1.30/execution/fs-texelFetchOffset-2D.c
> index 19e3654..de9a0f5 100644
> --- a/tests/spec/glsl-1.30/execution/fs-texelFetchOffset-2D.c
> +++ b/tests/spec/glsl-1.30/execution/fs-texelFetchOffset-2D.c
> @@ -76,7 +76,7 @@ piglit_display(void)
>  	bool pass = true;
>  	float red[4]   = {1.0, 0.0, 0.0, 1.0};
>  	float blue[4]  = {0.0, 0.0, 1.0, 1.0};
> -	float black[4] = {0.0, 0.0, 0.0, 1.0};
> +	float undefined[4] = {0.0, 0.0, 0.0, 0.0};
>  
>  	glClearColor(0.5, 0.5, 0.5, 1.0);
>  	glClear(GL_COLOR_BUFFER_BIT);
> @@ -92,12 +92,15 @@ piglit_display(void)
>  		for (q = 0; q < 4; q++) {
>  			const int tex_x = (q / 2) * ((width / 2));
>  			const int tex_y = (q % 2) * ((height / 2));
> -			float *c = black;
> +			float *c = undefined;
>  			const int x = 10+20*q;
>  
>  			/* fancy stuff - we should see red and blue
> -			   due to the offset for 3 levels, 
> -			   otherwise we get lots of black border color */
> +			   due to the offset for 3 levels, all the rest is
> +			   undefined due to out-of-bounds.
> +			   Only with ARB_robust_buffer_access_behavior
> +			   (and a robust context) the undefined result would
> +			   be guaranteed to be zero. */
>  			if (l < 3) {
>  				if (q == 2) c = red;
>  				else if (q == 3) c = blue;
> @@ -107,7 +110,7 @@ piglit_display(void)
>  			piglit_Uniform2i(pos_location, tex_x, tex_y);
>  			piglit_draw_rect(x, y, 10, 10);
>  
> -			if (width > 2) /* below 1 wide no test */
> +			if (width > 2 && c != undefined) /* below 1 wide no test */

The comment I was hoping for here would be:

			/* From the GL 3.0 spec, page 105 ("Texel Fetches"):
			 *
			 *     "The results of the texel fetch are
			 *      undefined if any of the following
			 *      conditions hold:
			 *
			 *      ...
			 *
			 *      - The texel coordinates refer to a
			 *        border texel outside of the defined
			 *        extents of the specified LOD"
			 */

>  				pass &= piglit_probe_rect_rgba(x, y, 10, 10, c);

Other than that, looks good.
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