[require]
GLSL >= 1.10

[vertex shader]
uniform float one;
uniform int index;

void main()
{
    /* Intentionally initialize the array in a non-ascending order. */
    vec4 array[4];
    array[2] = vec4(0.1, 0,   0,   0) * one;
    array[0] = vec4(0,   0.1, 0,   0) * one;
    array[3] = vec4(0,   0,   0.1, 0) * one;
    array[1] = vec4(0,   0.1, 0.1, 0) * one;
    array[index] = vec4(0.5, 0.5, 0.5, 0);
    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
    gl_FrontColor = array[0] + array[1] + array[2] + array[3];
}

[fragment shader file]
glsl-color.frag

[test]
ortho
clear color 0.5 0.5 0.5 0.5
clear
uniform float one 1
uniform int index 0
draw rect 10 10 10 10
probe rgb 15 15 0.6 0.6 0.7
uniform int index 1
draw rect 30 10 10 10
probe rgb 35 15 0.6 0.6 0.6
uniform int index 2
draw rect 50 10 10 10
probe rgb 55 15 0.5 0.7 0.7
uniform int index 3
draw rect 70 10 10 10
probe rgb 75 15 0.6 0.7 0.6