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

[Grigori Goronzy]

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