// quadratic bezier curve control point -> cubic bezier curve control points
void ComputeCubicCurveControlPoints(CGPoint p0, CGPoint c, CGPoint p1, CGPoint * c1, CGPoint * c2) {
    *c1 = CGPointMake((c.x * 2 + p0.x) / 3, (c.y * 2 + p0.y) / 3);
    *c2 = CGPointMake((c.x * 2 + p1.x) / 3, (c.y * 2 + p1.y) / 3);
}