[Mesa-dev] [PATCH 3/4] vbo: Rework checking of 'end' against _MaxElement.

[Kenneth Graunke]

This failed to take basevertex into account:

If basevertex < 0:
   (end + basevertex) might actually be in-bounds while 'end' is not.
   We would have clamped in this case when we probably shouldn't.
   This could break application drawing.

If basevertex > 0:
   'end' might be in-bounds while (end + basevertex) might not.
   We would have failed to clamp in this place.  There's a comment
   indicating the TNL module depends on max_index being in-bounds;
   if so, it would likely break horribly.

Rather than trying to clamp correctly in the face of basevertex, simply
delete the clamping code and indicate that we don't have a valid range.
This causes _tnl_vbo_draw_prims to use vbo_get_minmax_indices() to
compute the actual bounds, which is much safer.

NOTE: This is a candidate for release branches.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/vbo/vbo_exec_array.c |   17 ++++++-----------
 1 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/src/mesa/vbo/vbo_exec_array.c b/src/mesa/vbo/vbo_exec_array.c
index c26a8cd..67073df 100644
--- a/src/mesa/vbo/vbo_exec_array.c
+++ b/src/mesa/vbo/vbo_exec_array.c
@@ -859,6 +859,7 @@ vbo_exec_DrawRangeElementsBaseVertex(GLenum mode,
 				     GLint basevertex)
 {
    static GLuint warnCount = 0;
+   GLboolean index_bounds_valid = GL_TRUE;
    GET_CURRENT_CONTEXT(ctx);
 
    if (MESA_VERBOSE & VERBOSE_DRAW)
@@ -911,16 +912,6 @@ vbo_exec_DrawRangeElementsBaseVertex(GLenum mode,
       end = MIN2(end, 0xffff);
    }
 
-   if (end >= ctx->Array.ArrayObj->_MaxElement) {
-      /* Set 'end' to the max possible legal value */
-      assert(ctx->Array.ArrayObj->_MaxElement >= 1);
-      end = ctx->Array.ArrayObj->_MaxElement - 1;
-
-      if (end < start) {
-         return;
-      }
-   }
-
    if (0) {
       printf("glDraw[Range]Elements{,BaseVertex}"
 	     "(start %u, end %u, type 0x%x, count %d) ElemBuf %u, "
@@ -930,13 +921,17 @@ vbo_exec_DrawRangeElementsBaseVertex(GLenum mode,
 	     basevertex);
    }
 
+   if ((int)(end + basevertex) < 0 ||
+       end + basevertex >= ctx->Array.ArrayObj->_MaxElement)
+      index_bounds_valid = GL_FALSE;
+
 #if 0
    check_draw_elements_data(ctx, count, type, indices);
 #else
    (void) check_draw_elements_data;
 #endif
 
-   vbo_validated_drawrangeelements(ctx, mode, GL_TRUE, start, end,
+   vbo_validated_drawrangeelements(ctx, mode, index_bounds_valid, start, end,
 				   count, type, indices, basevertex, 1);
 }
 
-- 
1.7.7.6