[Mesa-dev] [PATCH] i965: Set the pre/post-blend color clamp flags.

[Kenneth Graunke]

On 09/22/2011 12:36 PM, Eric Anholt wrote:
> No change in piglit results on gen6.
> ---
>  src/mesa/drivers/dri/i965/gen6_cc.c |   20 ++++++++++++++++++++
>  1 files changed, 20 insertions(+), 0 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/gen6_cc.c b/src/mesa/drivers/dri/i965/gen6_cc.c
> index b8047d5..1e6c4cf 100644
> --- a/src/mesa/drivers/dri/i965/gen6_cc.c
> +++ b/src/mesa/drivers/dri/i965/gen6_cc.c
> @@ -99,6 +99,26 @@ prepare_blend_state(struct brw_context *brw)
>  					 eqA != eqRGB);
>        }
>  
> +      /* See section 8.1.6 "Pre-Blend Color Clamping" of the
> +       * SandyBridge PRM Volume 2 Part 1 for HW requirements.
> +       *
> +       * We do our ARB_color_buffer_float CLAMP_FRAGMENT_COLOR
> +       * clamping in the fragment shader.  For its clamping of
> +       * blending, the spec says:
> +       *
> +       *     "RESOLVED: For fixed-point color buffers, the inputs and
> +       *      the result of the blending equation are clamped.  For
> +       *      floating-point color buffers, no clamping occurs."
> +       *
> +       * So, generally, we want clamping to the render target's range.
> +       * And, good news, the hardware tables for both pre- and
> +       * post-blend color clamping are either ignored, or any are
> +       * allowed, or clamping is required but RT range clamping is a
> +       * valid option.
> +       */
> +      blend[b].blend1.pre_blend_clamp_enable = 1;
> +      blend[b].blend1.post_blend_clamp_enable = 1;
> +      blend[b].blend1.clamp_range = BRW_RENDERTARGET_CLAMPRANGE_FORMAT;
>  
>        /* _NEW_COLOR */
>        if (ctx->Color.AlphaEnabled) {

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>