th.sin(angle) * this.thickness / 2;
                const dyBottom = Math.cos(angle) * this.thickness / 2;

                if (i === 0) {
                    ctx.moveTo(p1.x + dxTop, p1.y + dyTop);
                } else {
                    ctx.lineTo(p1.x + dxTop, p1.y + dyTop);
                }
            }
            // 绘制下边缘 (反向)
            for (let i = this.points.length - 1; i > 0; i--) {
                const p1 = this.points[i];
                 // p2 is points[i-1] but we use p