[Mesa-dev] [PATCH 1/4] vbo: Remove pedantic warning about 'end' beind out of bounds.

[Brian Paul]

On 02/08/2012 06:08 AM, Kenneth Graunke wrote:
> The application supplied [start, end] range is merely a conservative
> hint of the ranges of index values inside the index buffer.  There is no
> requirement that all vertices in the range [start, end] be referenced.
>
> Passing an 'end' value larger than the maximum legal index is perfectly
> acceptible; applications can legally pass 0xffffffff when they don't
> have a tighter bound readily available.
>
> Thus, the warning doesn't indicate a correctness issue; it could only
> indicate a performance issue.  However, it does not even do that.
>
> glDrawRangeElements is designed to optimize non-VBO vertex data uploads
> by providing an upper bound on the size of buffers a driver would need
> to allocate.  With VBOs, the data is already in an uploaded buffer, so
> the range doesn't help.
>
> The clincher is: we only know _MaxElement for VBOs.  For user-space
> arrays, we just set it to 2,000,000,000 (see mesa/main/varray.h:63.)
> So we can only check this in the case where it is not useful.
>
> Many applications, including the Unigine demos, currently trigger this
> warning, which suggests the applications are buggy when they're actually
> fine.  Eliminating the warning should confuse users less while not
> actually losing any benefit to application developers.
>
> NOTE: This is a candidate for release branches.
>
> Suggested-by: Jose Fonseca<jfonseca at vmware.com>
> Signed-off-by: Kenneth Graunke<kenneth at whitecape.org>
> ---
>   src/mesa/vbo/vbo_exec_array.c |   49 +---------------------------------------
>   1 files changed, 2 insertions(+), 47 deletions(-)
>
> diff --git a/src/mesa/vbo/vbo_exec_array.c b/src/mesa/vbo/vbo_exec_array.c
> index d6b4d61..ec4cb4f 100644
> --- a/src/mesa/vbo/vbo_exec_array.c
> +++ b/src/mesa/vbo/vbo_exec_array.c
> @@ -708,6 +708,7 @@ vbo_exec_DrawArraysInstanced(GLenum mode, GLint start, GLsizei count,
>    * Map GL_ELEMENT_ARRAY_BUFFER and print contents.
>    * For debugging.
>    */
> +#if 0
>   static void
>   dump_element_buffer(struct gl_context *ctx, GLenum type)
>   {
> @@ -759,6 +760,7 @@ dump_element_buffer(struct gl_context *ctx, GLenum type)
>
>      ctx->Driver.UnmapBuffer(ctx, ctx->Array.ArrayObj->ElementArrayBufferObj);
>   }
> +#endif

Not a big deal, but someday I might wind up removing the #if 0 / 
#endif so that I can use this in gdb when debugging something.



>   /**
> @@ -856,7 +858,6 @@ vbo_exec_DrawRangeElementsBaseVertex(GLenum mode,
>   				     const GLvoid *indices,
>   				     GLint basevertex)
>   {
> -   static GLuint warnCount = 0;
>      GET_CURRENT_CONTEXT(ctx);
>
>      if (MESA_VERBOSE&  VERBOSE_DRAW)
> @@ -886,52 +887,6 @@ vbo_exec_DrawRangeElementsBaseVertex(GLenum mode,
>      }
>
>      if (end>= ctx->Array.ArrayObj->_MaxElement) {
> -      /* the max element is out of bounds of one or more enabled arrays */
> -      warnCount++;
> -
> -      if (warnCount<  10) {
> -         _mesa_warning(ctx, "glDraw[Range]Elements(start %u, end %u, count %d, "
> -                       "type 0x%x, indices=%p)\n"
> -                       "\tend is out of bounds (max=%u)  "
> -                       "Element Buffer %u (size %d)\n"
> -                       "\tThis should probably be fixed in the application.",
> -                       start, end, count, type, indices,
> -                       ctx->Array.ArrayObj->_MaxElement - 1,
> -                       ctx->Array.ArrayObj->ElementArrayBufferObj->Name,
> -                       (int) ctx->Array.ArrayObj->ElementArrayBufferObj->Size);
> -      }
> -
> -      if (0)
> -         dump_element_buffer(ctx, type);
> -
> -      if (0)
> -         _mesa_print_arrays(ctx);
> -
> -      /* 'end' was out of bounds, but now let's check the actual array
> -       * indexes to see if any of them are out of bounds.
> -       */
> -      if (0) {
> -         GLuint max = _mesa_max_buffer_index(ctx, count, type, indices,
> -                                             ctx->Array.ArrayObj->ElementArrayBufferObj);
> -         if (max>= ctx->Array.ArrayObj->_MaxElement) {
> -            if (warnCount<  10) {
> -               _mesa_warning(ctx, "glDraw[Range]Elements(start %u, end %u, "
> -                             "count %d, type 0x%x, indices=%p)\n"
> -                             "\tindex=%u is out of bounds (max=%u)  "
> -                             "Element Buffer %u (size %d)\n"
> -                             "\tSkipping the glDrawRangeElements() call",
> -                             start, end, count, type, indices, max,
> -                             ctx->Array.ArrayObj->_MaxElement - 1,
> -                             ctx->Array.ArrayObj->ElementArrayBufferObj->Name,
> -                             (int) ctx->Array.ArrayObj->ElementArrayBufferObj->Size);
> -            }
> -         }
> -         /* XXX we could also find the min index and compare to 'start'
> -          * to see if start is correct.  But it's more likely to get the
> -          * upper bound wrong.
> -          */
> -      }
> -
>         /* Set 'end' to the max possible legal value */
>         assert(ctx->Array.ArrayObj->_MaxElement>= 1);
>         end = ctx->Array.ArrayObj->_MaxElement - 1;

Reviewed-by: Brian Paul <brianp at vmware.com>