e feedback if typed
                        updateLevel(parseInt(this.subdivisionLevelInput.value, 10));
                    });
                }
            }

            _coonsifyPatch() {
                if (!this.mainPatch) return;
                const p = this.mainPatch.points;

                // P[1][1]
                let sum11 = createPoint(0,0);
                sum11 = addPoints(sum11, scalePoint(p[0][0], -4.0));
                sum11 = addPoints(sum11, scalePoint(addPoints(p[0][1], p[1][0]), 6