[Mesa-dev] [PATCH 3/6] i965: Stop using BRW_RASTRULE_LOWER_RIGHT on Gen4-5.

[Rafael Antognolli]

Reviewed-by: Rafael Antognolli <rafael.antognolli at intel.com>

On Wed, May 10, 2017 at 11:47:27AM -0700, Kenneth Graunke wrote:
> This effectively reverts Robert Ellison's 2009 commit
> cc8afbd3862fedfe42e51c3774960d1c7078ec53.
> 
> I'm not seeing any GL spec text indicating that UPPER won't work.
> On Gen6+, this bit moved to 3DSTATE_WM as a single bit, controlling
> UPPER_LEFT vs. UPPER_RIGHT.  There is no way to request LOWER_RIGHT,
> so UPPER_RIGHT is the best you can do.
> 
> In the G45 docs, it's marked as "Reserved" as well, but we just
> decided to use it anyway.
> 
> This patch unifies the behavior between Gen4-5 and Gen6+.
> 
> Note that this is separate from point sprite texcoord behavior.
> ---
>  src/mesa/drivers/dri/i965/brw_sf_state.c | 28 +---------------------------
>  1 file changed, 1 insertion(+), 27 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_sf_state.c b/src/mesa/drivers/dri/i965/brw_sf_state.c
> index d5e586d1bf3..30a9f5d5e43 100644
> --- a/src/mesa/drivers/dri/i965/brw_sf_state.c
> +++ b/src/mesa/drivers/dri/i965/brw_sf_state.c
> @@ -227,33 +227,7 @@ static void upload_sf_unit( struct brw_context *brw )
>     else if (sf->sf6.line_width <= 0x2)
>         sf->sf6.line_width = 0;
>  
> -   /* _NEW_BUFFERS */
> -   if (!render_to_fbo) {
> -      /* Rendering to an OpenGL window */
> -      sf->sf6.point_rast_rule = BRW_RASTRULE_UPPER_RIGHT;
> -   }
> -   else {
> -      /* If rendering to an FBO, the pixel coordinate system is
> -       * inverted with respect to the normal OpenGL coordinate
> -       * system, so BRW_RASTRULE_LOWER_RIGHT is correct.
> -       * But this value is listed as "Reserved, but not seen as useful"
> -       * in Intel documentation (page 212, "Point Rasterization Rule",
> -       * section 7.4 "SF Pipeline State Summary", of document
> -       * "Intel® 965 Express Chipset Family and Intel® G35 Express
> -       * Chipset Graphics Controller Programmer's Reference Manual,
> -       * Volume 2: 3D/Media", Revision 1.0b as of January 2008,
> -       * available at
> -       *     https://01.org/linuxgraphics/documentation/hardware-specification-prms
> -       * at the time of this writing).
> -       *
> -       * It does work on at least some devices, if not all;
> -       * if devices that don't support it can be identified,
> -       * the likely failure case is that points are rasterized
> -       * incorrectly, which is no worse than occurs without
> -       * the value, so we're using it here.
> -       */
> -      sf->sf6.point_rast_rule = BRW_RASTRULE_LOWER_RIGHT;
> -   }
> +   sf->sf6.point_rast_rule = BRW_RASTRULE_UPPER_RIGHT;
>  
>     /* _NEW_POINT */
>     sf->sf7.sprite_point = ctx->Point.PointSprite;
> -- 
> 2.12.2
> 
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