[require]
GLSL >= 1.10

[vertex shader]
varying vec2 pos;
void main()
{
	gl_Position = gl_Vertex;
	pos = gl_Vertex.xy;
}

[fragment shader]
varying vec2 pos;
void main()
{
	gl_FragColor = vec4(atan(pos.y, pos.x) / (2.0 * 3.1415926) + 0.5);
}

[test]
draw rect -1 -1 2 2
relative probe rgba (1.0, 0.5) (0.5, 0.5, 0.5, 0.5)
relative probe rgba (1.0, 1.0) (0.625, 0.625, 0.625, 0.625)
relative probe rgba (0.5, 1.0) (0.75, 0.75, 0.75, 0.75)
relative probe rgba (0.0, 1.0) (0.875, 0.875, 0.875, 0.875)
# discontinuity here.  See glsl-fs-atan-2 for that.
# relative probe rgba (0.0, 0.5) (1.0, 1.0, 1.0, 1.0)
relative probe rgba (0.0, 0.0) (0.125, 0.125, 0.125, 0.125)
relative probe rgba (0.5, 0.0) (0.25, 0.25, 0.25, 0.25)
relative probe rgba (1.0, 0.0) (0.375, 0.375, 0.375, 0.375)