[Mesa-dev] [PATCH 4/6] i965: Clarify that we only check one prim's type for cut index support.

[Paul Berry]

On 30 August 2013 10:36, Eric Anholt <eric at anholt.net> wrote:

> Kenneth Graunke <kenneth at whitecape.org> writes:
>
> > can_cut_index_handle_prims() was passed an array of _mesa_prim objects
> > and a count, and runs a loop for that many iterations.  However, it
> > treats the array like a pointer, repeatedly checking the first element.
> >
> > This is wasteful and bizarre.
> >
> > The VBO module will never call us with multiple primitives of different
> > topologies, so it's actually reasonable to just check the first element.
>
> I'm pretty sure it will.  I don't see anything in vbo_exec_Begin()
> making sure the new primitive is the same type as the last.
>

Yeah, I agree.  Although I wasn't able to construct a failing case using
primitive restart, I did verify by experiment that this sequence of calls
causes the VBO module to call us with multiple primitives of different
types:

glBegin(GL_LINE_STRIP);
glArrayElement(...);
...
glEnd();
glBegin(GL_LINE_LOOP);
glArrayElement(...);
...
glEnd();

Given that nr_prims only gets large when glBegin/glEnd is in use, I don't
think we have to worry about performance in the loop.  Let's just correct
the loop to check all prims, which was almost certainly the original intent.
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