float x = radius;
float y = 0;
float cx = center.x;
float cy = center.y;
gl.glBegin(GL2.GL_LINE_LOOP);
gl.glColor4f(color.x, color.y, color.z, 1);
for (int i = 0; i < NUM_CIRCLE_POINTS; i++) {
gl.glVertex3f(x + cx, y + cy, 0);
// apply the rotation matrix
float temp = x;
x = c * x - s * y;