[Mesa-dev] [PATCH 10/11] i965/gen6: Add support for point min/max size from ARB_point_parameters.

[Kenneth Graunke]

On 05/12/2011 09:05 PM, Eric Anholt wrote:
> Fixes glean pointAtten.
> ---
>   src/mesa/drivers/dri/i965/gen6_sf_state.c |    9 +++++++--
>   1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> index 50a5ad3..f96cfe5 100644
> --- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
> +++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> @@ -103,6 +103,7 @@ upload_sf_state(struct brw_context *brw)
>      int attr = 0;
>      int urb_start;
>      int two_side_color = (ctx->Light.Enabled&&  ctx->Light.Model.TwoSide);
> +   float point_size;
>
>      /* _NEW_TRANSFORM */
>      if (ctx->Transform.ClipPlanesEnabled)
> @@ -209,8 +210,12 @@ upload_sf_state(struct brw_context *brw)
>   	 ctx->Point._Attenuated))
>         dw4 |= GEN6_SF_USE_STATE_POINT_WIDTH;
>
> -   dw4 |= U_FIXED(CLAMP(ctx->Point.Size, 0.125, 255.875), 3)<<
> -      GEN6_SF_POINT_WIDTH_SHIFT;
> +   /* Clamp to ARB_point_parameters user limits */
> +   point_size = CLAMP(ctx->Point.Size, ctx->Point.MinSize, ctx->Point.MaxSize);
> +
> +   /* Clamp to the hardware limits, in fixed point */
> +   dw4 |= CLAMP(U_FIXED(point_size, 3), 1, 0x7ff);
> +
>      if (ctx->Point.SpriteOrigin == GL_LOWER_LEFT)
>         dw1 |= GEN6_SF_POINT_SPRITE_LOWERLEFT;

Why the change to clamp in fixed point?  Unless it's necessary for 
correctness, I'd prefer to stick with 0.125 and 255.875, since those are 
directly readable/searchable in the hardware documentation, while 0x7ff 
is not.

What about:
/* Clamp to ARB_point_parameters user limits */
point_size = CLAMP(ctx->Point.Size, ctx->Point.MinSize, ctx->Point.MaxSize);
/* Clamp to the hardware limits and convert to fixed point */
dw4 |= U_FIXED(CLAMP(point_size, 0.125, 255.875), 3);

--Kenneth