[Piglit] [PATCH] gs: less demanding tests for triangle strips.

[Paul Berry]

On 5 September 2013 17:52, Matt Turner <mattst88 at gmail.com> wrote:

> On Wed, Aug 28, 2013 at 1:59 PM, Paul Berry <stereotype441 at gmail.com>
> wrote:
> > +[vertex shader]
> > +#version 150
>
> We don't need to specify the #version anymore, now that it's added by
> shader_runner, given the [require] section.
>

Argh, you're right.  I keep forgetting about that.  Fixed.


>
> > +
> > +in vec4 vertex;
> > +out vec4 vertex_to_gs;
> > +
> > +void main()
> > +{
> > +  vertex_to_gs = vertex;
> > +}
> > +
> > +[geometry shader]
> > +#version 150
> > +
> > +layout(triangles_adjacency) in;
> > +layout(triangle_strip, max_vertices = 3) out;
> > +
> > +in vec4 vertex_to_gs[6];
> > +
> > +void main()
> > +{
> > +  for (int i = 0; i < 3; i++) {
> > +    gl_Position = vertex_to_gs[2*i];
>
> If I understand correctly, in the first geometry shader invocation
> this will emit vertices 1, 3, and 5 from your picture. Is that what
> you're referring to when you say "the first triangle is clockwise"?
>
> I wasn't clear whether you meant the triangle 1-2-3, or 1-3-5. From
> the comment and picture I'd have thought the first, and from the code
> I'd have thought the second. Both, as it turn out are clockwise.
>

Your understanding from the code is correct.  Triangle 1-2-3's orientation
isn't really significant for this particular test, since it is an "adjacent
triangle".  The vertices comprising the adjacent triangles are tested
adequately by triangle-strip-adj.shader_test.

I've updated the comment to look like this:

# Note that the only triangles drawn by this test are triangles 1-3-5,
# 5-3-7, 5-7-9, and 9-7-11.  The other triangles shown in the diagram
# are "adjacent triangles".
#
# Note also that triangles 1-3-5, 5-3-7, 5-7-9, and 9-7-11 are all
# clockwise, so we expect gl_FrontFacing to be false.

Is that clear enough, or should I explain in more detail?


>
> Once I understand that,
>
> Reviewed-by: Matt Turner <mattst88 at gmail.com>
>
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