bow&arrow

要点一：射箭施加力的方式

            arrow.GetComponent<Rigidbody>().AddForce (Quaternion.Euler (new Vector3(transform.rotation.eulerAngles.x,transform.rotation.eulerAngles.y,transform.rotation.eulerAngles.z))*new Vector3(25f*length,0,0), ForceMode.VelocityChange);

Quaternion.Euler 欧拉角

返回一个旋转角度，绕z轴旋转z度，绕x轴旋转x度，绕y轴旋转y度（像这样的顺序）

四元数和向量相乘

Quaternion.Euler(x,y,z) 返回一个绕x轴旋转x度再绕y轴旋转y度再绕z轴旋转z度的Quaternion,              因此Quaternion.Euler(0,90,0)返回一个绕y轴旋转90度的旋转操作.Quaternion作用于Vector3的右乘操作（*）返回一个将向量做旋转操作后的向量.                                     因此Quaternion.Euler(0,90,0)*Vector3(0.0,0.0,-10)表示将向量Vector3(0.0,0.0,-10)做绕y轴90度旋转后的结果.因该等于Vector3(-10,0,0).

ForceMode.VelocityChange
Unity中关于作用力方式ForceMode的功能注解

此种作用方式下将忽略刚体的实际质量，采用默认质量1.0，同时也忽略系统的实际帧频间隔，采用默认间隔1.0，即f•1.0=1.0•v

要点二：计算射箭方向

public void prepareArrow() {
        // get the touch point on the screen
        mouseRay1 = Camera.main.ScreenPointToRay(Input.mousePosition);
        if (Physics.Raycast(mouseRay1, out rayHit, 1000f) && arrowShot == false)
        {
            // determine the position on the screen
            posX = this.rayHit.point.x;
            posY = this.rayHit.point.y;
            // set the bows angle to the arrow
            Vector2 mousePos = new Vector2(transform.position.x-posX,transform.position.y-posY);
            float angleZ = Mathf.Atan2(mousePos.y,mousePos.x)*Mathf.Rad2Deg;
            transform.eulerAngles = new Vector3(0,0,angleZ);
            // determine the arrow pullout
            length = mousePos.magnitude / 3f;
            length = Mathf.Clamp(length,0,1);
            // set the bowstrings line renderer
            stringPullout = new Vector3(-(0.44f+length), -0.06f, 2f);
            // set the arrows position
            Vector3 arrowPosition = arrow.transform.localPosition;
            arrowPosition.x = (arrowStartX - length);
            arrow.transform.localPosition = arrowPosition;
        }
        arrowPrepared = true;
    }

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