[require] GLSL >= 1.10 [vertex shader] void main() { gl_Position = gl_Vertex; } [fragment shader] uniform vec4 color; uniform float add; void main() { gl_FragColor = ((1.0 + color) + add) + -0.5; } [test] uniform float add -0.5 uniform vec4 color 0.0 1.0 0.0 0.0 draw rect -1 -1 2 2 probe all rgba 0.0 1.0 0.0 0.0