llvmpipe: consolidate scissor plane code between line/tri

This code is pretty much the same in both, consolidate it.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12504>

src/gallium/drivers/llvmpipe/lp_setup.c

@@ -1752,4 +1752,58 @@ lp_setup_flush_and_restart(struct lp_setup_context *setup)
    return TRUE;
 }
 
-
+void
+lp_setup_add_scissor_planes(const struct u_rect *scissor,
+                            struct lp_rast_plane *plane_s,
+                            boolean s_planes[4])
+{
+   /*
+    * When rasterizing scissored tris, use the intersection of the
+    * triangle bounding box and the scissor rect to generate the
+    * scissor planes.
+    *
+    * This permits us to cut off the triangle "tails" that are present
+    * in the intermediate recursive levels caused when two of the
+    * triangles edges don't diverge quickly enough to trivially reject
+    * exterior blocks from the triangle.
+    *
+    * It's not really clear if it's worth worrying about these tails,
+    * but since we generate the planes for each scissored tri, it's
+    * free to trim them in this case.
+    *
+    * 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 (s_planes[0]) {
+      plane_s->dcdx = ~0U << 8;
+      plane_s->dcdy = 0;
+      plane_s->c = (1-scissor->x0) << 8;
+      plane_s->eo = 1 << 8;
+      plane_s++;
+   }
+   if (s_planes[1]) {
+      plane_s->dcdx = 1 << 8;
+      plane_s->dcdy = 0;
+      plane_s->c = (scissor->x1+1) << 8;
+      plane_s->eo = 0 << 8;
+      plane_s++;
+   }
+   if (s_planes[2]) {
+      plane_s->dcdx = 0;
+      plane_s->dcdy = 1 << 8;
+      plane_s->c = (1-scissor->y0) << 8;
+      plane_s->eo = 1 << 8;
+      plane_s++;
+   }
+   if (s_planes[3]) {
+      plane_s->dcdx = 0;
+      plane_s->dcdy = ~0U << 8;
+      plane_s->c = (scissor->y1+1) << 8;
+      plane_s->eo = 0;
+      plane_s++;
+   }
+}

src/gallium/drivers/llvmpipe/lp_setup_context.h

@@ -207,6 +207,10 @@ scissor_planes_needed(boolean scis_planes[4], const struct u_rect *bbox,
    scis_planes[3] = (bbox->y1 > scissor->y1);
 }
 
+void
+lp_setup_add_scissor_planes(const struct u_rect *scissor,
+                            struct lp_rast_plane *plane_s,
+                            boolean s_planes[4]);
 
 void lp_setup_choose_triangle( struct lp_setup_context *setup );
 void lp_setup_choose_line( struct lp_setup_context *setup );

src/gallium/drivers/llvmpipe/lp_setup_line.c

@@ -711,60 +711,8 @@ try_setup_line( struct lp_setup_context *setup,
       if (plane[i].dcdy > 0) plane[i].eo += plane[i].dcdy;
    }
 
-
-   /* 
-    * When rasterizing scissored tris, use the intersection of the
-    * triangle bounding box and the scissor rect to generate the
-    * scissor planes.
-    *
-    * This permits us to cut off the triangle "tails" that are present
-    * in the intermediate recursive levels caused when two of the
-    * triangles edges don't diverge quickly enough to trivially reject
-    * exterior blocks from the triangle.
-    *
-    * It's not really clear if it's worth worrying about these tails,
-    * but since we generate the planes for each scissored tri, it's
-    * free to trim them in this case.
-    * 
-    * 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 > 4) {
-      struct lp_rast_plane *plane_s = &plane[4];
-
-      if (s_planes[0]) {
-         plane_s->dcdx = ~0U << 8;
-         plane_s->dcdy = 0;
-         plane_s->c = (1-scissor->x0) << 8;
-         plane_s->eo = 1 << 8;
-         plane_s++;
-      }
-      if (s_planes[1]) {
-         plane_s->dcdx = 1 << 8;
-         plane_s->dcdy = 0;
-         plane_s->c = (scissor->x1+1) << 8;
-         plane_s->eo = 0 << 8;
-         plane_s++;
-      }
-      if (s_planes[2]) {
-         plane_s->dcdx = 0;
-         plane_s->dcdy = 1 << 8;
-         plane_s->c = (1-scissor->y0) << 8;
-         plane_s->eo = 1 << 8;
-         plane_s++;
-      }
-      if (s_planes[3]) {
-         plane_s->dcdx = 0;
-         plane_s->dcdy = ~0U << 8;
-         plane_s->c = (scissor->y1+1) << 8;
-         plane_s->eo = 0;
-         plane_s++;
-      }
-      assert(plane_s == &plane[nr_planes]);
+      lp_setup_add_scissor_planes(scissor, &plane[4], s_planes);
    }
 
    return lp_setup_bin_triangle(setup, line, &bbox, &bboxpos, nr_planes, viewport_index);

src/gallium/drivers/llvmpipe/lp_setup_tri.c

@@ -734,60 +734,8 @@ do_triangle_ccw(struct lp_setup_context *setup,
                    plane[2].eo);
    }
 
-
-   /* 
-    * When rasterizing scissored tris, use the intersection of the
-    * triangle bounding box and the scissor rect to generate the
-    * scissor planes.
-    *
-    * This permits us to cut off the triangle "tails" that are present
-    * in the intermediate recursive levels caused when two of the
-    * triangles edges don't diverge quickly enough to trivially reject
-    * exterior blocks from the triangle.
-    *
-    * It's not really clear if it's worth worrying about these tails,
-    * but since we generate the planes for each scissored tri, it's
-    * free to trim them in this case.
-    * 
-    * 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 > 3) {
-      struct lp_rast_plane *plane_s = &plane[3];
-
-      if (s_planes[0]) {
-         plane_s->dcdx = ~0U << 8;
-         plane_s->dcdy = 0;
-         plane_s->c = (1-scissor->x0) << 8;
-         plane_s->eo = 1 << 8;
-         plane_s++;
-      }
-      if (s_planes[1]) {
-         plane_s->dcdx = 1 << 8;
-         plane_s->dcdy = 0;
-         plane_s->c = (scissor->x1+1) << 8;
-         plane_s->eo = 0 << 8;
-         plane_s++;
-      }
-      if (s_planes[2]) {
-         plane_s->dcdx = 0;
-         plane_s->dcdy = 1 << 8;
-         plane_s->c = (1-scissor->y0) << 8;
-         plane_s->eo = 1 << 8;
-         plane_s++;
-      }
-      if (s_planes[3]) {
-         plane_s->dcdx = 0;
-         plane_s->dcdy = ~0U << 8;
-         plane_s->c = (scissor->y1+1) << 8;
-         plane_s->eo = 0;
-         plane_s++;
-      }
-      assert(plane_s == &plane[nr_planes]);
+      lp_setup_add_scissor_planes(scissor, &plane[3], s_planes);
    }
 
    return lp_setup_bin_triangle(setup, tri, &bbox, &bboxpos, nr_planes, viewport_index);