[Piglit] [PATCH 1/2] Add a test of tessellation of transform feedback primitives.

[Eric Anholt]

On Tue,  8 Nov 2011 16:03:39 -0800, Paul Berry <stereotype441 at gmail.com> wrote:
> According to the OpenGL 3.0 spec (section 2.15: Transform Feedback):
> 
>     "When quads and polygons are provided to transform feedback with a
>     primitive mode of TRIANGLES, they will be tessellated and recorded
>     as triangles (the order of tessellation within a primitive is
>     undefined). Individual lines or triangles of a strip or fan
>     primitive will be extracted and recorded separately."
> 
> This test verifies the correctness of the tessellation and extraction
> from strips and fans.  It does so by feeding the output of transform
> feedback back into the GL pipeline and verifying that the rendered
> image is the same.
> 
> Verified using the nVidia proprietary driver for Linux.  The nVidia
> driver passes all tests except "tessellation polygon flat_last",
> "tessellation quad_strip flat_last", and "tessellation quads
> flat_last".  These tests fail because the order in which the driver
> tessellates polygons and quads fails to preserve the correct provoking
> vertex, leading to different results from flatshading.

Ensuring that provoking vertex is respected seems like a reasonable
requirement, and at least our hardware is built to support it it looks
like.

I like the test idea, and have just a few little style comments.  I find
the vertex transformations a bit unintuitive compared to most of our
tests, but I'm not really worried.

> +#include "piglit-util.h"
> +
> +#ifndef M_PI
> +#define M_PI 3.141592653589793
> +#endif

M_PI?

> +#define BUFFER_SIZE 20
> +
> +#define Elements(array) (sizeof(array)/sizeof(array[0]))

There's ARRAY_SIZE available so you don't have to redefine this.

> +/**
> + * Check that two strips of the window match.  Strips are numbered
> + * from the top from 0 to 3.
> + */
> +static GLboolean
> +match_strips(int reference, int compare)
> +{
> +	int reference_offset = (3 - reference) * (piglit_height / 4);
> +	int compare_offset = (3 - compare) * (piglit_height / 4);
> +	int x, y;
> +	for (x = 0; x < piglit_width; ++x) {
> +		for (y = 0; y < piglit_height/4; ++y) {
> +			float probed[4];
> +			glReadPixels(x, y + reference_offset, 1, 1,
> +				     GL_RGBA, GL_FLOAT, &probed);
> +			if (!piglit_probe_pixel_rgba(x, y + compare_offset,
> +						     probed))
> +				return GL_FALSE;
> +		}
> +	}
> +	return GL_TRUE;
> +}

It would be nice if you could use piglit_probe_rect_halves_equal_rgba()
or a derivative here.  glReadPixels()ing each pixel one by one sucks for
performance.

> +			printf("Test requires GL_EXT_provoking_vertex "
> +			       "or GL_ARB_provoking_vertex\n");
> +			piglit_report_result(PIGLIT_SKIP);
> +			exit(1);

piglit_report_result() implies exit()
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