[Mesa-dev] [PATCH] i965: Remove interleaved user array upload optimization

[Eric Anholt]

Ian Romanick <idr at freedesktop.org> writes:

> From: Ian Romanick <ian.d.romanick at intel.com>
>
> The checks to determine when the data can be uploaded in an interleaved
> fashion can be tricked by certain data layouts.  For example,
>
>     float data[...];
>
>     glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 16, &data[0]);
>     glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 16, &data[4]);
>     glDrawArrays(GL_POINTS, 0, 1);
>
> will hit the interleaved path with an incorrect size (16 bytes instead
> of 32 bytes).  As a result, the data for attribute 1 never gets
> uploaded.  The single element draw case is the only sensible case I can
> think of for non-interleaved-that-looks-like-interleaved data, but there
> may be others as well.
>
> I don't see an easy way to fix the checks, so I have chosen to just rip
> out the optimization.  This may cause performance issues on applications
> that use large arrays of data that are not in VBOs.

Check that count * strideb actually contains the data you're hoping to
read from the later attributes?  Seems pretty doable.

As is, this hurts cairo-gl performance by 1.9034% +/- 0.441538%
(n=33/34, 3 throttling outliers removed)
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