[require] GLSL >= 1.10 [vertex shader] void main() { gl_Position = gl_Vertex; } [fragment shader] uniform vec4 color; void main() { vec4 c1 = color * 0.5; vec4 c2 = c1; if (color.x < 1.0) { c1 *= 2.0; } gl_FragColor = c2; } [test] uniform vec4 color 0.0 1.0 0.0 0.0 draw rect -1 -1 2 2 probe all rgba 0.0 0.5 0.0 0.0