1 files changed, 51 insertions, 30 deletions

diff --git a/src/gallium/drivers/llvmpipe/lp_setup_line.c b/src/gallium/drivers/llvmpipe/lp_setup_line.c
index f425825fc2a..f6e1198d036 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_line.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup_line.c
@@ -336,13 +336,6 @@ try_setup_line( struct lp_setup_context *setup,
       layer = MIN2(layer, scene->fb_max_layer);
    }
 
-   if (setup->scissor_test) {
-      nr_planes = 8;
-   }
-   else {
-      nr_planes = 4;
-   }
-
    dx = v1[0][0] - v2[0][0];
    dy = v1[0][1] - v2[0][1];
    area = (dx * dx  + dy * dy);
@@ -591,6 +584,20 @@ try_setup_line( struct lp_setup_context *setup,
    bbox.x0 = MAX2(bbox.x0, 0);
    bbox.y0 = MAX2(bbox.y0, 0);
 
+   nr_planes = 4;
+   /*
+    * Determine how many scissor planes we need, that is drop scissor
+    * edges if the bounding box of the tri is fully inside that edge.
+    */
+   if (setup->scissor_test) {
+      /* why not just use draw_regions */
+      struct u_rect *scissor = &setup->scissors[viewport_index];
+      nr_planes += (bbox.x0 < scissor->x0);
+      nr_planes += (bbox.x1 > scissor->x1);
+      nr_planes += (bbox.y0 < scissor->y0);
+      nr_planes += (bbox.y1 > scissor->y1);
+   }
+
    line = lp_setup_alloc_triangle(scene,
                                   key->num_inputs,
                                   nr_planes,
@@ -708,30 +715,44 @@ try_setup_line( struct lp_setup_context *setup,
     * Note that otherwise, the scissor planes only vary in 'C' value,
     * and even then only on state-changes.  Could alternatively store
     * these planes elsewhere.
+    * (Or only store the c value together with a bit indicating which
+    * scissor edge this is, so rasterization would treat them differently
+    * (easier to evaluate) to ordinary planes.)
     */
-   if (nr_planes == 8) {
-      const struct u_rect *scissor =
-         &setup->scissors[viewport_index];
-
-      plane[4].dcdx = -1 << 8;
-      plane[4].dcdy = 0;
-      plane[4].c = (1-scissor->x0) << 8;
-      plane[4].eo = 1 << 8;
-
-      plane[5].dcdx = 1 << 8;
-      plane[5].dcdy = 0;
-      plane[5].c = (scissor->x1+1) << 8;
-      plane[5].eo = 0;
-
-      plane[6].dcdx = 0;
-      plane[6].dcdy = 1 << 8;
-      plane[6].c = (1-scissor->y0) << 8;
-      plane[6].eo = 1 << 8;
-
-      plane[7].dcdx = 0;
-      plane[7].dcdy = -1 << 8;
-      plane[7].c = (scissor->y1+1) << 8;
-      plane[7].eo = 0;
+   if (nr_planes > 4) {
+      /* why not just use draw_regions */
+      struct u_rect *scissor = &setup->scissors[viewport_index];
+      struct lp_rast_plane *plane_s = &plane[4];
+
+      if (bbox.x0 < scissor->x0) {
+         plane_s->dcdx = -1 << 8;
+         plane_s->dcdy = 0;
+         plane_s->c = (1-scissor->x0) << 8;
+         plane_s->eo = 1 << 8;
+         plane_s++;
+      }
+      if (bbox.x1 > scissor->x1) {
+         plane_s->dcdx = 1 << 8;
+         plane_s->dcdy = 0;
+         plane_s->c = (scissor->x1+1) << 8;
+         plane_s->eo = 0 << 8;
+         plane_s++;
+      }
+      if (bbox.y0 < scissor->y0) {
+         plane_s->dcdx = 0;
+         plane_s->dcdy = 1 << 8;
+         plane_s->c = (1-scissor->y0) << 8;
+         plane_s->eo = 1 << 8;
+         plane_s++;
+      }
+      if (bbox.y1 > scissor->y1) {
+         plane_s->dcdx = 0;
+         plane_s->dcdy = -1 << 8;
+         plane_s->c = (scissor->y1+1) << 8;
+         plane_s->eo = 0;
+         plane_s++;
+      }
+      assert(plane_s == &plane[nr_planes]);
    }
 
    return lp_setup_bin_triangle(setup, line, &bbox, nr_planes, viewport_index);