[Mesa-dev] Mesa (master): st/mesa & v_bug_mgr: two small instanced drawing fixes

[Christian König]

Am Montag, den 28.02.2011, 08:32 -0800 schrieb Brian Paul:
....
>> diff --git a/src/mesa/state_tracker/st_draw.c b/src/mesa/state_tracker/st_draw.c
....
> >            min_index = MIN2(min_index, prims[i].start);
> >            max_index = MAX2(max_index, prims[i].start + prims[i].count - 1);
> > +         max_index = MAX2(max_index, prims[i].num_instances);
....

> I don't understand that last bit.  If we're doing regular, 
> non-instanced drawing, prims[i].num_instances will be 1.  So max_index 
> will always be one.  That doesn't seem right.
The maximum check is additional to the existing calculation, not a
replacement. So max_index only gets increased if the number of instances
to draw is higher than the number of vertices.

But indeed that's just a workaround to make piglits
draw-instanced-divisor test happy. max_index seems to be used to
calculate the size of the buffer needed to hold the vertex data, but in
the case of instanced drawing this isn't correct.

@Marek:
Since you are the author of the code maybe you could help here out a
bit. Where is max_index used to calculate the buffer size? I couldn't
find a call to the buffer creation function. The size calculation
somewhere around this call needs to be adopted to the case when we draw
more instances than vertices or indexes.

Christian.