[Mesa-dev] [PATCH V3 05/13] mesa: Add validation helpers for new indirect draws

Kenneth Graunke kenneth at whitecape.org
Tue Nov 12 12:57:44 PST 2013

On 11/12/2013 12:35 PM, Paul Berry wrote:
> On 12 November 2013 12:13, Kenneth Graunke <kenneth at whitecape.org
> <mailto:kenneth at whitecape.org>> wrote:
>     It would be great to put a citation for this:
>     /* From the ARB_multi_draw_indirect specification:
>      * "INVALID_VALUE is generated by MultiDrawArraysIndirect or
>      *  MultiDrawElementsIndirect if <primcount> is negative."
>      *
>      * "<primcount> must be positive, otherwise an INVALID_VALUE error will
>      *  be generated."
>      */
>     These beg the question of whether 0 is allowed.  Usually I interpret
>     "negative" as < 0, "positive" as >= 0, and "strictly positive" as > 0.
>     So I think zero should be allowed, and I don't see a contradiction.
>     The only text I can find in 4.3 and 4.4 just reiterate that it needs to
>     positive, and I don't see any text defining "positive."
> In the absence of text defining "positive", shouldn't we go with the
> definition used by mathematicians?  According to
> http://en.wikipedia.org/wiki/Sign_%28mathematics%29#Terminology_for_signs,
> "positive" means strictly greater than zero.

Mathematicians are inconsistent in their use of terminology.  Positive
can mean either > 0 or >= 0 depending who you talk to and in what
context.  And the GL specification authors are notoriously non-precise.

> If anyone is aware of a competing implementation that accepts a
> primcount of 0, then I'd be open to following the behaviour of the
> competing implementation (and filing a spec bug).  But otherwise I think
> we should prohibit zero.

Then I suppose I have to go test AMD or nVidia.

> (Note: I brought this up last time the patch was reviewed:
> http://lists.freedesktop.org/archives/mesa-dev/2013-November/047962.html)

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