Android 围绕一点旋转手势的角度计算

方法一(余弦定理)：

private double getRotate(double x1, double y1, double x2, double y2) {
        double abx = centerX - x1;
        double aby = centerY - y1;
        double acx = centerX - x2;
        double acy = centerY - y2;
        double bcx = x2 - x1;
        double bcy = y2 - y1;

        double c = Math.hypot(abx,aby);
        Log.e("TAG","c == " + c);
        double b = Math.hypot(acx,acy);
        Log.e("TAG","b == " + b);
        double a = Math.hypot(bcx,bcy);
        Log.e("TAG","a == " + a);
        double cos1 = (c*c + b*b - a*a)/(2*b*c);
        Log.e("TAG","cos == " + cos1);
        if (cos1 >= 1) {
            cos1 = 1f;
        }
        double radian = Math.acos(cos1);
        double degree = Math.toDegrees(radian);
}

方法二：

private double getRotate(double x1, double y1, double x2, double y2) {
        double v1 = (abx * acx) + (aby * acy);
        double abx = centerX - x1;
        double aby = centerY - y1;
        double acx = centerX - x2;
        double acy = centerY - y2;
        double bcx = x2 - x1;
        double bcy = y2 - y1;
        double abL = Math.sqrt(abx*abx + aby*aby);
        double acL = Math.sqrt(acx*acx + acy*acy);
        double cos = v1 / (abL*acL);
        Log.e("TAG","cos1 == " + cos);
        double radian = Math.acos(cos);

        double degree = Math.toDegrees(radian);

        return degree;
}

3 鸿洋的圆形菜单的方法

/**
* 算出该点与水平的角度的值，用移动点角度减去起始点角度就是旋转角度。
*/
private double getAngle(double xTouch, double yTouch) {
        double x = xTouch - centerX;
        double y = yTouch - centerY;
        return (double) (Math.asin(y / Math.hypot(x, y)) * 180 / Math.PI);
    }

1