[require]
GLSL >= 1.10

[vertex shader]
void main()
{
	gl_Position = gl_Vertex;
}

[fragment shader]
uniform float v;
void main()
{
	gl_FragColor = vec4(0.0) - v;
}

[test]
uniform float v -0.5
draw rect -1 -1 2 2
probe all rgba 0.5 0.5 0.5 0.5