Hi Marek,
Back on Jan 10 you removed the per-vertex array max_index field
(commit cdca3c58aa2d9549f5188910e2a77b438516714f). I believe this was
a mistake.
I noticed today that the piglit draw-instanced-divisor test is
failing. A bisection points to Jose's commit
17bbc1f0425b3768e26473eccea5f2570dcb26d3. But that's a red herring.
If I disable the SSE code paths, the regression goes back to the Jan
10 change.
With the GL_ARB_instanced_arrays extension vertex array indexing
changes quite a bit. Specifically, some arrays (those with divisors
!= 0) are now indexed by instance ID, not the primitive's vertex
index. The draw_info::max_index field doesn't let us take this into
account. I believe that we really need a per-array max_index value.
As an example, suppose we're drawing a star field with 1 million
instanced stars, each star drawn as a 4-vertex quad. We might use a
vertex array indexed by the instance ID to color the stars.
The draw call would look like:
glDrawArraysInstanced(GL_QUADS, 0, 4, 1000*1000);
In this case we'd have two vertex arrays. The first array is the quad
vertex positions with four elements. The second array is the star
colors with 1 million elements. As it is now, we're setting
draw_info::max_index = 4 and we errantly clamp the index into the
second array to 4 instead of 1 million.
As a temporary work around we can disable clamping of array indexes
for instance arrays. But I think we need to revert the Jan 10 commit
and then rework some of Jose's related changes.
-Brian
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