[require]
GLSL >= 1.10

[vertex shader]
varying float x;
void main()
{
	gl_Position = gl_Vertex;
	x = gl_Vertex.x;
}

[fragment shader]
varying float x;
void main()
{
	/* The interpolated x at the pixels next to the window bounds will
	 * be just > 0.0 or < 1.0 by 1/width.  Correct for that.
	 */
	float adjusted_x = x * (1.0 + 1.0 / 256.0);
	gl_FragColor = vec4(asin(adjusted_x) / 3.1415926 + 0.5);
}

[test]
draw rect -1 -1 2 2
relative probe rgba (0.0, 0.5) (0.0, 0.0, 0.0, 0.0)
relative probe rgba (0.1464, 0.5) (0.25, 0.25, 0.25, 0.25)
relative probe rgba (0.5, 0.5) (0.5, 0.5, 0.5, 0.5)
relative probe rgba (0.8535, 0.5) (0.75, 0.75, 0.75, 0.75)
relative probe rgba (1.0, 0.5) (1.0, 1.0, 1.0, 1.0)