1void main() {
2   gl_Position = gl_Vertex;
3   vec4 sum = vec4(0);
4   for (int i = 1; i != 2; i += 2) {
5      sum += vec4(0.1, 0.1, 0.1, 0.1);
6   }
7   gl_FrontColor = sum;
8}
9