[require]
GLSL >= 1.10

[fragment shader]
uniform float a;
uniform float b;
void main(void)
{
	struct S {
		float a;
		float b;
		float c;
		float d;
	} s = S(0.5, 0.5, 0.5, 0.5);

	s.a = s.a + a;
	s.a = s.a - b;
	gl_FragColor = vec4(s.a, s.b, s.c, s.d);
}

[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