[Mesa-dev] [PATCH 2/2] radeonsi: use guard band clipping

[Marek Olšák]

There is one small issue with this. It uses viewport extents clamped
to [0, 16384], but it should use unclamped signed coordinates of the
viewport. The hw clipper doesn't do any clamping, so it's easy to
generate window coordinates outside of [-32768, 32768] if the viewport
covers [-32768, 1] in one dimension and the guard band is > 1 in
that dimension.

Marek

On Wed, Apr 6, 2016 at 10:15 PM, Grigori Goronzy <greg at chown.ath.cx> wrote:
> With the previous changes to handling of viewport clipping, it is
> almost trivial to add proper support for guard band clipping.  Select a
> suitable integer clipping value to keep inside the rasterizer's guard
> band range of [-32768, 32767] and program the hardware to use guard
> band clipping.
>
> Guard band clipping speeds up rasterization for primitives that are
> partially off-screen.  This change in particular results in small
> framerate improvements in a wide range of games.
> ---
>  src/gallium/drivers/radeonsi/si_state.c | 34 ++++++++++++++++++++++++++++++---
>  1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/src/gallium/drivers/radeonsi/si_state.c b/src/gallium/drivers/radeonsi/si_state.c
> index 0bb41e5..013fcf1 100644
> --- a/src/gallium/drivers/radeonsi/si_state.c
> +++ b/src/gallium/drivers/radeonsi/si_state.c
> @@ -882,9 +882,19 @@ static void si_clip_scissor(struct pipe_scissor_state *out,
>         out->maxy = MIN2(out->maxy, clip->maxy);
>  }
>
> +static void si_mix_scissor(struct pipe_scissor_state *out,
> +                          struct pipe_scissor_state *clip)
> +{
> +       out->minx = MIN2(out->minx, clip->minx);
> +       out->miny = MIN2(out->miny, clip->miny);
> +       out->maxx = MAX2(out->maxx, clip->maxx);
> +       out->maxy = MAX2(out->maxy, clip->maxy);
> +}
> +
>  static void si_emit_one_scissor(struct radeon_winsys_cs *cs,
>                                 struct pipe_viewport_state *vp,
> -                               struct pipe_scissor_state *scissor)
> +                               struct pipe_scissor_state *scissor,
> +                               struct pipe_scissor_state *mix)
>  {
>         struct pipe_scissor_state final;
>
> @@ -895,6 +905,7 @@ static void si_emit_one_scissor(struct radeon_winsys_cs *cs,
>
>         if (scissor)
>                 si_clip_scissor(&final, scissor);
> +       si_mix_scissor(mix, &final);
>
>         radeon_emit(cs, S_028250_TL_X(final.minx) |
>                         S_028250_TL_Y(final.miny) |
> @@ -903,19 +914,35 @@ static void si_emit_one_scissor(struct radeon_winsys_cs *cs,
>                         S_028254_BR_Y(final.maxy));
>  }
>
> +static void si_emit_guardband(struct si_context *sctx,
> +                             struct pipe_scissor_state *scissor)
> +{
> +       struct radeon_winsys_cs *cs = sctx->b.gfx.cs;
> +
> +       int width = scissor->maxx - scissor->minx;
> +       int height = scissor->maxy - scissor->miny;
> +       float guardband_x = width ? (32768 / width) : 1.0;
> +       float guardband_y = height ? (32768 / height) : 1.0;
> +
> +       radeon_set_context_reg(cs, R_028BF0_PA_CL_GB_HORZ_CLIP_ADJ, fui(guardband_x));
> +       radeon_set_context_reg(cs, R_028BE8_PA_CL_GB_VERT_CLIP_ADJ, fui(guardband_y));
> +}
> +
>  static void si_emit_scissors(struct si_context *sctx, struct r600_atom *atom)
>  {
>         struct radeon_winsys_cs *cs = sctx->b.gfx.cs;
>         struct pipe_scissor_state *states = sctx->scissors.states;
>         unsigned mask = sctx->scissors.dirty_mask;
>         bool scissor_enable = sctx->queued.named.rasterizer->scissor_enable;
> +       struct pipe_scissor_state max_clip = {0};
>
>         /* The simple case: Only 1 viewport is active. */
>         if (mask & 1 &&
>             !si_get_vs_info(sctx)->writes_viewport_index) {
>                 radeon_set_context_reg_seq(cs, R_028250_PA_SC_VPORT_SCISSOR_0_TL, 2);
>                 si_emit_one_scissor(cs, &sctx->viewports.states[0],
> -                                   scissor_enable ? &states[0] : NULL);
> +                                   scissor_enable ? &states[0] : NULL, &max_clip);
> +               si_emit_guardband(sctx, &max_clip);
>                 sctx->scissors.dirty_mask &= ~1; /* clear one bit */
>                 return;
>         }
> @@ -929,9 +956,10 @@ static void si_emit_scissors(struct si_context *sctx, struct r600_atom *atom)
>                                                start * 4 * 2, count * 2);
>                 for (i = start; i < start+count; i++) {
>                         si_emit_one_scissor(cs, &sctx->viewports.states[i],
> -                                           scissor_enable ? &states[i] : NULL);
> +                                           scissor_enable ? &states[i] : NULL, &max_clip);
>                 }
>         }
> +       si_emit_guardband(sctx, &max_clip);
>         sctx->scissors.dirty_mask = 0;
>  }
>
> --
> 1.9.1
>
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