[require]
GLSL >= 1.10

[vertex shader]
varying vec4 color;

void main()
{
	gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
	vec4 vc = vec4(gl_Vertex.x - 2.0,
		       gl_Vertex.x + 2.0,
		       gl_Vertex.y + 2.0,
		       gl_Vertex.y - 2.0);

	color = clamp(vc, 0.0, 1.0);
}

[fragment shader]
varying vec4 color;

void main()
{
	gl_FragColor = color * 0.5 + 0.25;
}

[test]
draw rect -1 -1 2 2
probe all rgba 0.25 0.75 0.75 0.25