[require]
GLSL >= 1.10

[fragment shader]
uniform float a;
uniform float b;
void main(void)
{
	mat2 m = mat2(0.5, 0.5, 0.5, 0.5);
	m[0][0] = m[0][0] + a;
	m[0][0] = m[0][0] - b;
	gl_FragColor = vec4(m[0][0], m[0][1], m[1][0], m[1][1]);
}

[test]
uniform float a 0.3
uniform float b 0.3
draw rect -1 -1 2 2
probe all rgba 0.5 0.5 0.5 0.5