> -----Original Message-----
> From: Ian Romanick [mailto:i...@freedesktop.org]
> Sent: Wednesday, September 09, 2015 8:54 PM
> To: Predut, Marius; mesa-dev@lists.freedesktop.org
> Subject: Re: [Mesa-dev] [PATCH v2] i915: fixing driver crashes if too few
> vertices are submitted
>
> On 09/09/2015 11:16 AM, Marius Predut wrote:
> > Comparison with a signed expression and unsigned value
> > is converted to unsigned value, reason for minus value is interpreted
> > as a big unsigned value. For this case the "for" loop
> > is going into unexpected behavior.
> >
> > v1:Brian Paul: code style fix.
>
> I don't think you really did...
>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38109
> > Signed-off-by: Marius Predut <marius.pre...@intel.com>
> > ---
> > src/mesa/tnl_dd/t_dd_dmatmp.h | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/mesa/tnl_dd/t_dd_dmatmp.h b/src/mesa/tnl_dd/t_dd_dmatmp.h
> > index 7be3954..79de224 100644
> > --- a/src/mesa/tnl_dd/t_dd_dmatmp.h
> > +++ b/src/mesa/tnl_dd/t_dd_dmatmp.h
> > @@ -627,6 +627,9 @@ static void TAG(render_quads_verts)( struct gl_context
> *ctx,
> > LOCAL_VARS;
> > GLuint j;
> >
> > + if(count % 4 != 0)
> ^
> ...because I'm quite sure Brian's code had a space here, per Mesa's
> coding standards.
So code style is: if( count % 4 != 0 )?
I think Brian used: if(count % 4 != 0)
>
> Also, this change is incorrect. If an application does
> glDrawArrays(GL_QUADS, 0, (n * 4) + 3), this change will cause zero
> quads to be drawn when n quads should be drawn.
>
> Page 18 (page 32 of the PDF) of the OpenGL 2.1 spec says:
>
> "The total number of vertices between Begin and End is 4n + k,
> where 0 ≤ k ≤ 3; if k is not zero, the final k vertices are
> ignored."
>
> We probably don't have a piglit test for this scenario, so one should be
> added. You can CC me on that patch. :)
Ok
>
> I think the correct change is to trim count such that (count % 4) == 0.
> If the modified value of count is zero, bail out. With that change,
> the other hunk (below) is unnecessary.
>
> > + return;
> > +
> > INIT(GL_TRIANGLES);
> >
> > for (j = start; j < count-3; j += 4) {
> > @@ -1248,7 +1251,7 @@ static GLboolean TAG(validate_render)( struct
> gl_context *ctx,
> > ok = (GLint) count < GET_SUBSEQUENT_VB_MAX_ELTS();
> > }
> > else {
> > - ok = HAVE_TRIANGLES; /* flatshading is ok. */
> > + ok = HAVE_TRIANGLES && (count % 4 == 0); /* flatshading is ok. */
> > }
> > break;
> > default:
> >
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