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

[Kenneth Graunke]

On 02/08/2012 06:59 AM, Brian Paul wrote:
> 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.

Yeah, it looked like useful functionality, so I wanted to keep it, but I 
was getting an "unused function" warning.