[Mesa-dev] [Mesa3d-dev] r300g: hack around issue with doom3 and 0 stride

[Roland Scheidegger]

What's wrong with the stride zero concept?
I think most hw can handle this just fine (pretty sure all radeons
should, though of course driver might need some special case code if it
uses this to determine max index due to zero division). Apparently, you
could optimize it away on nv hardware, and some hardware might not like
it at all and hence needs to turn it into a constant, but is it really
necessary to do away with it at a higher level?
It might not be optimal to refetch the same vertex attribute over and
over again, but then the app looks poorly optimized to begin with if it
doesn't use a constant.

Roland


On 11.04.2010 08:54, Keith Whitwell wrote:
> I'd like to get rid of the zero stride concept and require the state  
> tracker to either turn those values into proper constant (easy now we  
> can bind >1 constant buffer) or use instancing to get the same effect.
> 
> Keith
> 
> 
> On 11 Apr 2010, at 00:27, Zack Rusin <zackr at vmware.com> wrote:
> 
>> On Saturday 10 April 2010 18:44:27 Luca Barbieri wrote:
>>>> r300g: hack around issue with doom3 and 0 stride
>>>>
>>>> This is most likely a bug in the mesa state tracker, but do the  
>>>> quick
>>>> hack for now to avoid the divide by 0.
>>> This is not a bug: stride 0 means that the vertex attribute is
>>> constant for all vertices.
>> Right, it's how our vbo code handles cases like
>> glBegin(primitive);
>> glColor4f(...);
>> glVertex(...);
>> glVertex(...);
>> glVertex(...);
>> glEnd();
>>
>>> Thus, the patch is not likely to be correct: you should instead  
>>> either
>>> program stride 0 to the hardware if supported, or fetch the vertex
>>> attribute with the CPU
>> Dave, jfyi, i implemented this a long time ago in svga, just search  
>> for
>> zero_stride in there (svga_hw_update_zero_stride in particular), you  
>> should be
>> able to almost simply copy&paste that code.
>>
>> z
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