[Mesa-dev] [PATCH] i965: fix inverted point sprite origin when rendering to FBO

[Eric Anholt]

On Thu, 19 Jan 2012 10:30:53 +0800, Yuanhan Liu <yuanhan.liu at linux.intel.com> wrote:
> When rendering to FBO, rendering is inverted. At the same time, we would
> also make sure the point sprite origin is inverted. Or, we will get an
> inverted result correspoinding to rendering to the default winsys FBO.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44613
> 
> NOTE: This is a candidate for stable release branches.
> 
> v2: add the simliar logic to ivb, too (comments from Ian)
>     simplify the logic operation (comments from Brian)
> 
> Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_defines.h   |    1 +
>  src/mesa/drivers/dri/i965/gen6_sf_state.c |   15 +++++++++++++--
>  src/mesa/drivers/dri/i965/gen7_sf_state.c |   20 +++++++++++++++++---
>  3 files changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
> index 4d90a99..029be87 100644
> --- a/src/mesa/drivers/dri/i965/brw_defines.h
> +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> @@ -1128,6 +1128,7 @@ enum brw_message_target {
>  /* DW1 (for gen6) */
>  # define GEN6_SF_NUM_OUTPUTS_SHIFT			22
>  # define GEN6_SF_SWIZZLE_ENABLE				(1 << 21)
> +# define GEN6_SF_POINT_SPRITE_UPPERLEFT			(0 << 20)
>  # define GEN6_SF_POINT_SPRITE_LOWERLEFT			(1 << 20)
>  # define GEN6_SF_URB_ENTRY_READ_LENGTH_SHIFT		11
>  # define GEN6_SF_URB_ENTRY_READ_OFFSET_SHIFT		4
> diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> index 548c5a3..67c208b 100644
> --- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
> +++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> @@ -129,6 +129,7 @@ upload_sf_state(struct brw_context *brw)
>     float point_size;
>     uint16_t attr_overrides[FRAG_ATTRIB_MAX];
>     bool userclip_active;
> +   uint32_t point_sprite_origin;
>  
>     /* _NEW_TRANSFORM */
>     userclip_active = (ctx->Transform.ClipPlanesEnabled != 0);
> @@ -258,8 +259,18 @@ upload_sf_state(struct brw_context *brw)
>     /* Clamp to the hardware limits and convert to fixed point */
>     dw4 |= U_FIXED(CLAMP(point_size, 0.125, 255.875), 3);
>  
> -   if (ctx->Point.SpriteOrigin == GL_LOWER_LEFT)
> -      dw1 |= GEN6_SF_POINT_SPRITE_LOWERLEFT;
> +   /*
> +    * When rendering to FBO, rendering is inverted. At the same time,
> +    * we would also make sure the point sprite origin is inverted.
> +    * Or, we will get an inverted result corresponding to rendering
> +    * to the default/window FBO.
> +    */

I think this comment could be simplified to "Window coordinates in an
FBO are inverted, which means point sprite origin must be inverted."

> +   if ((ctx->Point.SpriteOrigin == GL_LOWER_LEFT) ^ render_to_fbo) {
> +      point_sprite_origin = GEN6_SF_POINT_SPRITE_LOWERLEFT;
> +   } else {
> +      point_sprite_origin = GEN6_SF_POINT_SPRITE_UPPERLEFT;
> +   }

Much better.  That logic was hideous before.
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