[Mesa-dev] Mesa (primitive-restart): 682 new commits

Brian Paul brianp at vmware.com
Thu Aug 12 06:28:56 PDT 2010

On 08/12/2010 07:16 AM, Keith Whitwell wrote:
> On Thu, 2010-08-12 at 06:08 -0700, Brian Paul wrote:
>> On 08/11/2010 09:40 PM, Luca Barbieri wrote:
>>> [Apparently brianp at kemper.freedesktop.org is forwarded to
>>> brian.paul at tungstengraphics.com, which is no longer valid.]
>>>    I'd suggest to put it in struct pipe_index_buffer.
>>>    The argument is that the index buffer needs to be prepared
>>>    specifically for the primitive restart enable setting:
>>>    1. If the index buffer has no restart indices, using primitive restart
>>>    will have no effect
>>>    2. If the index buffer has restart indices, not using primitive
>>>    restart will cause out-of-bounds accesses or weird rendering results
>>>    Also, the index size is there too, so there is no question of what
>>>    happens if the primitive restart index doesn't fit in the index size.
>>>    Currently the Mesa state tracker binds the index buffer for every draw
>>>    call, and thus would be unaffected (but it should stop doing that).
>> The thing is, primitive restart also applies to non-indexed
>> primitives.  It would be a little weird to set index buffer state for
>> glDrawArrays calls.
> Wow, that's a pretty wierd case.  So if you set the primitive restart
> value to 32 then draw_arrays(TRISTRIP, 0, 64), you'll get two strips??

Yup.  If one implements glDrawArrays() and glDrawElements() in terms 
of glArrayElement() it kind of makes sense, but it's not too useful. 
It would have been more useful for glDrawArrays() if the restart index 
were periodic.  Then the primitive would be restarted after every N 
vertices, rather than just one restart at i==N.


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