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# Check proper functioning of the gl_PrimitiveID fragment shader
# input, in the case where there is no geometry shader, and provoking vertex
# is set to first vertex.
[require]
GLSL >= 1.50
GL_EXT_provoking_vertex
[vertex shader]
#version 150
in vec4 piglit_vertex;
flat out int vertex_id;
void main()
{
gl_Position = piglit_vertex;
vertex_id = gl_VertexID;
}
[fragment shader]
#version 150
flat in int vertex_id;
void main()
{
/* We draw a triangle fan containing 6 vertices, so the relationship between
* the primitive ID and the input vertex ID's should be:
*
* Primitive ID Vertex ID's Provoking vertex ID
* 0 0 1 2 1
* 1 0 2 3 2
* 2 0 3 4 3
* 3 0 4 5 4
*
* Since vertex_id uses interpolation qualifier "flat", it should
* always receive the value from the provoking vertex. Therefore,
* by the table above, it should always be 1 greater than the
* expected value of gl_PrimitiveID.
*/
int expected_primitive_id = vertex_id - 1;
if (expected_primitive_id == gl_PrimitiveID)
gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
else
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}
[vertex data]
piglit_vertex/float/2
-1.0 -1.0
-1.0 1.0
0.0 1.0
1.0 1.0
1.0 0.0
1.0 -1.0
[test]
clear color 0.0 0.0 0.0 0.0
clear
provoking vertex first
draw arrays GL_TRIANGLE_FAN 0 6
probe all rgba 0.0 1.0 0.0 1.0
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