#version 130

attribute vec4 vPosition;

out vec4   color;

int Quadrant(float x, float y);

uniform float theta = 0;

void main() {
    float distance;
    float red = 0.0,
          green = 0.0,
          blue = 0.0;

    distance = sqrt(pow(vPosition.x,2.0)+pow(vPosition.y,2.0));


    switch(Quadrant(vPosition.x, vPosition.y)) {
       case 1:
           red = distance; 
	   break;
       case 2:
           green = distance; 
	   break;
       case 3: 
           blue = distance; 
	   break;
       case 4: 
           red = distance; 
	   blue = distance; 
	   break;
       default:
           red = 1.0;
	   green = 1.0;
	   blue = 1.0;
    }

    color = vec4(red, green, blue, 1.0);

    gl_Position = vPosition * mat4(   cos(theta), sin(theta), 0, 0,
                                     -sin(theta), cos(theta), 0, 0,
				      0,          0,          1, 0,
				      0,          0,          0, 1);
    gl_PointSize = 5.0;
}

int Quadrant(float x, float y) {

    int quadrant;

    if (x < 0.0 ) {
        if (y < 0.0) {
	   quadrant = 3;
	} else {
	   quadrant = 2;
	}
    } else {
        if (y < 0.0) {
	   quadrant = 4;
	} else {
	   quadrant = 1;
	}
    }

    return quadrant;
}