gallium/draw: add limits to the clip and cull distances

There are strict limits on those registers. Define the maximums
and use them instead of magic numbers. Also allows us to add
some extra sanity checks.
Suggested by Brian.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/auxiliary/draw/draw_context.c

@@ -738,6 +738,7 @@ draw_current_shader_clipvertex_output(const struct draw_context *draw)
 uint
 draw_current_shader_clipdistance_output(const struct draw_context *draw, int index)
 {
+   debug_assert(index < PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
    if (draw->gs.geometry_shader)
       return draw->gs.geometry_shader->clipdistance_output[index];
    return draw->vs.clipdistance_output[index];
@@ -756,6 +757,7 @@ draw_current_shader_num_written_clipdistances(const struct draw_context *draw)
 uint
 draw_current_shader_culldistance_output(const struct draw_context *draw, int index)
 {
+   debug_assert(index < PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
    if (draw->gs.geometry_shader)
       return draw->gs.geometry_shader->culldistance_output[index];
    return draw->vs.vertex_shader->culldistance_output[index];

src/gallium/auxiliary/draw/draw_gs.c

@@ -792,13 +792,13 @@ draw_create_geometry_shader(struct draw_context *draw,
       if (gs->info.output_semantic_name[i] == TGSI_SEMANTIC_VIEWPORT_INDEX)
          gs->viewport_index_output = i;
       if (gs->info.output_semantic_name[i] == TGSI_SEMANTIC_CLIPDIST) {
-         if (gs->info.output_semantic_index[i] == 0)
+         debug_assert(gs->info.output_semantic_index[i] <
-            gs->clipdistance_output[0] = i;
+                      PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
-         else
+         gs->clipdistance_output[gs->info.output_semantic_index[i]] = i;
-            gs->clipdistance_output[1] = i;
       }
       if (gs->info.output_semantic_name[i] == TGSI_SEMANTIC_CULLDIST) {
-         debug_assert(gs->info.output_semantic_index[i] < Elements(gs->culldistance_output));
+         debug_assert(gs->info.output_semantic_index[i] <
+                      PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
          gs->culldistance_output[gs->info.output_semantic_index[i]] = i;
       }
    }

src/gallium/auxiliary/draw/draw_gs.h

@@ -67,8 +67,8 @@ struct draw_geometry_shader {
    struct tgsi_shader_info info;
    unsigned position_output;
    unsigned viewport_index_output;
-   unsigned clipdistance_output[2];
+   unsigned clipdistance_output[PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT];
-   unsigned culldistance_output[2];
+   unsigned culldistance_output[PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT];
 
    unsigned max_output_vertices;
    unsigned primitive_boundary;

src/gallium/auxiliary/draw/draw_vs.c

@@ -86,12 +86,12 @@ draw_create_vertex_shader(struct draw_context *draw,
             found_clipvertex = TRUE;
             vs->clipvertex_output = i;
          } else if (vs->info.output_semantic_name[i] == TGSI_SEMANTIC_CLIPDIST) {
-            if (vs->info.output_semantic_index[i] == 0)
+            debug_assert(vs->info.output_semantic_index[i] <
-               vs->clipdistance_output[0] = i;
+                         PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
-            else
+            vs->clipdistance_output[vs->info.output_semantic_index[i]] = i;
-               vs->clipdistance_output[1] = i;
          } else if (vs->info.output_semantic_name[i] == TGSI_SEMANTIC_CULLDIST) {
-            debug_assert(vs->info.output_semantic_index[i] < Elements(vs->culldistance_output));
+            debug_assert(vs->info.output_semantic_index[i] <
+                         PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT);
             vs->culldistance_output[vs->info.output_semantic_index[i]] = i;
          }
       }

src/gallium/auxiliary/draw/draw_vs.h

@@ -112,8 +112,8 @@ struct draw_vertex_shader {
    unsigned position_output;
    unsigned edgeflag_output;
    unsigned clipvertex_output;
-   unsigned clipdistance_output[2];
+   unsigned clipdistance_output[PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT];
-   unsigned culldistance_output[2];
+   unsigned culldistance_output[PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT];
    /* Extracted from shader:
     */
    const float (*immediates)[4];

src/gallium/docs/source/tgsi.rst

@@ -2435,6 +2435,29 @@ float32 signed distance to a plane. Primitives will be completely
 discarded if the plane distance for all of the vertices in the
 primitive are < 0. If a vertex has a cull distance of NaN, that
 vertex counts as "out" (as if its < 0);
+The limits on both clip and cull distances are bound
+by the PIPE_MAX_CLIP_OR_CULL_DISTANCE_COUNT define which defines
+the maximum number of components that can be used to hold the
+distances and by the PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT
+which specifies the maximum number of registers which can be
+annotated with those semantics.
+
+
+TGSI_SEMANTIC_CLIPDIST
+""""""""""""""""""""""
+
+When components of vertex elements are identified this way, these
+values are each assumed to be a float32 signed distance to a plane.
+Primitive setup only invokes rasterization on pixels for which
+the interpolated plane distances are >= 0. Multiple clip planes
+can be implemented simultaneously, by annotating multiple
+components of one or more vertex elements with the above specified
+semantic. The limits on both clip and cull distances are bound
+by the PIPE_MAX_CLIP_OR_CULL_DISTANCE_COUNT define which defines
+the maximum number of components that can be used to hold the
+distances and by the PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT
+which specifies the maximum number of registers which can be
+annotated with those semantics.
 
 
 Declaration Interpolate

src/gallium/include/pipe/p_state.h

@@ -66,6 +66,8 @@ extern "C" {
 #define PIPE_MAX_SO_BUFFERS        4
 #define PIPE_MAX_SO_OUTPUTS       64
 #define PIPE_MAX_VIEWPORTS        16
+#define PIPE_MAX_CLIP_OR_CULL_DISTANCE_COUNT 8
+#define PIPE_MAX_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT 2
 
 
 struct pipe_reference