[require]
GLSL >= 1.10

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

[fragment shader]
uniform vec4 arg0;
varying float xval;
varying float yval;
void main()
{
	gl_FragColor = vec4(dFdx(-xval) * -20.0,
                            dFdy(-yval) * -10.0,
                            0.0, 1.0);
}

[test]
draw rect -1 -1 2 2
probe rgba  16  16 0.16 0.08 0.00 1.00