[require] GLSL >= 1.10 [vertex shader] uniform float i; void main() { vec4 color = vec4(0.0, 0.0, 1.0, 0.0); color.y = color[int(i)]; color.z = 0.0; gl_FrontColor = color; gl_Position = gl_Vertex; } [fragment shader file] glsl-color.frag [test] uniform float i 2.0; draw rect -1 -1 2 2 probe rgb 1 1 0.0 1.0 0.0