in src/ras.rs [292:299]
fn curve_to(&mut self, x1: f32, y1: f32, x2: f32, y2: f32, x: f32, y: f32) {
self.contour.push_cubic(
Vector2F::new(x1, y1),
Vector2F::new(x2, y2),
Vector2F::new(x, y),
);
self.path.cubic_to(x1, y1, x2, y2, x, y);
}