計(jì)算公式

• 弧度制角度轉(zhuǎn)換
  弧度 = π / 180 * 角度
  角度 = 180 / π * 弧度

• 圓心坐標(biāo) (a, b) P點(diǎn)坐標(biāo)(x0, y0) 弧度 α
  x1 = a + (x0 - a) * cosα - (y0 - b) * sinα
  y1 = b + (x0 - a) * sinα + (y0 - b) * cosα

  /**
    * 通過當(dāng)前P點(diǎn)和旋轉(zhuǎn)角度計(jì)算旋轉(zhuǎn)之前的點(diǎn)
    */
    computePosition(x: number, y: number, angle: number): {x: number, y: number} {
        // 圓心
        let a: number = this.img.anchorOffsetX;
        let b: number = this.img.anchorOffsetY;
        // 計(jì)算
        let c: number = -Math.PI / 180 * angle;
        let rx: number = (x - a) * Math.cos(c) - (y - b) * Math.sin(c) + a;
        let ry: number = (y - b) * Math.cos(c) + (x - a) * Math.sin(c) + b;
        // 取整
        rx = Math.round(rx);
        ry = Math.round(ry);
        return { x: rx, y: ry };
    }