#version 120

void main(void)
{
	gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
	
	float x = gl_Position.x;
	float y = gl_Position.y;
	float z = gl_Position.z;

	int depth = int(sqrt(x * x + y * y + z * z));

	if (depth < 800) {
		depth = 0;
	}

        if (depth > 9000) {
          depth = 9000;
        }

        float fRed = 0;
        float fBlue = 0;
        float fGreen = 0;

        if (depth < 1500) {
          int adj_depth = depth;
          // Red to yellow
          fRed = 1.0;
          fGreen = float(adj_depth) / 1500;
        }
        if (depth >= 1500 && depth < 3000) {
          // Yellow to green
          int adj_depth = depth - 1500;
          fGreen = 1.0;
          fRed = 1.0 - (float(adj_depth) / 1500);
        }
        if (depth >= 3000 && depth < 4500) {
          // Green to Cyan
          int adj_depth = depth - 3000;
          fGreen = 1.0;
          fBlue = float(adj_depth) / 1500;
        }       
        if (depth >= 4500 && depth < 6000) {
          // Cyan to Blue
          int adj_depth = depth - 4500;
          fBlue = 1.0;
          fGreen = 1.0 - (float(adj_depth) / 1500);
        }
        if (depth >= 6000 && depth < 7500) {
          // Blue to Magenta
          int adj_depth = depth - 6000;
          fBlue = 1.0;
          fRed = float(adj_depth) / 1500;
        }
        if (depth >= 1500 && depth < 3000) {
          // Magenta to Red
          int adj_depth = depth - 7500;
          fRed = 1.0;
          fBlue = 1.0 - (float(adj_depth) / 1500);
        }

	gl_FrontColor = vec4(fRed, fGreen, fBlue, 1.0);
}