使用Unity实现VR中在黑板上写字（升级篇）（一）-----解决画笔穿透画板的问题

internal Plane boardPlane;

   private voidStart()
    {
        //初始化Plane，让它的法线是这个画板的forward向量，并且法线通过画板的中心位置，由此确定一个平面
        boardPlane = newPlane(transform.forward, transform.position);
......
}

/// <summary>
    ///判断笔尖是在画板的正面还是背面
    /// </summary>
    /// <param name="point">笔尖的位置</param>
    /// <returns>true 在正面;false 在背面</returns>
    public boolGetSideOfBoardPlane(Vector3 point)
    {
        returnboardPlane.GetSide(point);
    }
    /// <summary>
    ///笔尖与平面的距离
    /// </summary>
    /// <param name="point">笔尖的位置</param>
    /// <returns>当在正面的时候返回正值，当在背面的时候返回负值</returns>
    public floatGetDistanceFromBoardPlane(Vector3 point)
    {
        returnboardPlane.GetDistanceToPoint(point);
    }
    /// <summary>
    ///矫正后的笔尖应该在的位置
    /// </summary>
    /// <param name="point">笔尖的位置</param>
    /// <returns>矫正后的笔尖位置</returns>
    publicVector3 ProjectPointOnBoardPlane(Vector3 point)
    {
        float d = -Vector3.Dot(boardPlane.normal, point -transform.position);
        return point + boardPlane.normal *d;
    }

usingVRTK.GrabAttachMechanics;
usingUnityEngine;
public classPainterGrabAttach : VRTK_BaseGrabAttach
{
    [Header("Painter Options")]
    [SerializeField]
    private Transform tips;//笔尖
    private static Board board;//画板
    #region 重写的父类方法
    protected override voidInitialise()
    {
        //初始化父类的一些字段，这些字段只是标识这个抓附机制的作用
        tracked = false;
        kinematic = false;
        climbable = false;
        //初始化自定义的属性
        if (precisionGrab)//最好不要用精确抓取，因为这样很有可能会让笔处于一个不合理的位置，这样使用的时候，会很变扭（比如必须手腕旋转一个角度，笔才是正的） 
{
            Debug.LogError("PrecisionGrab cant't be true in case of PainterGrabAttach Mechanic");
        }
        board = FindObjectOfType<Board>();
    }
    public override boolStartGrab(GameObject grabbingObject, GameObject givenGrabbedObject, Rigidbody givenControllerAttachPoint)
    {
        if (base.StartGrab(grabbingObject, givenGrabbedObject, givenControllerAttachPoint))
        {
            SnapObjectToGrabToController(givenGrabbedObject);
            grabbedObjectScript.IsKinematic = true;
            return true;
        }
        return false;
    }
    public override void StopGrab(boolapplyGrabbingObjectVelocity)
    {
        ReleaseObject(applyGrabbingObjectVelocity);
        base.StopGrab(applyGrabbingObjectVelocity);
    }
    public override voidProcessFixedUpdate()
    {
        if (grabbedObject)//只有抓住物体后，grabbedObject才不会
{
            grabbedObject.transform.rotation = controllerAttachPoint.transform.rotation *Quaternion.Euler(grabbedSnapHandle.transform.localEulerAngles);
            grabbedObject.transform.position = controllerAttachPoint.transform.position - (grabbedSnapHandle.transform.position -grabbedObject.transform.position);
            float distance = board.GetDistanceFromBoardPlane(tips.position);//笔尖距离平面的距离
            bool isPositiveOfBoardPlane = board.GetSideOfBoardPlane(tips.position);//笔尖是不是在笔尖的正面
            Vector3 direction = grabbedObject.transform.position - tips.position;//笔尖位置指向笔的位置的差向量
            //当笔尖穿透的时候，需要矫正笔的位置 
            if (isPositiveOfBoardPlane || distance > 0.0001f)
            {
                Vector3 pos =board.ProjectPointOnBoardPlane(tips.position);
                grabbedObject.transform.position = pos - board.boardPlane.normal * 0.001f + direction;//pos是笔尖的位置，而不是笔的位置，加上direction后才是笔的位置 
}
        }
    }
    #endregion
    //让手柄抓住物体
    private voidSnapObjectToGrabToController(GameObject obj)
    {
        if (!precisionGrab)
        {
            SetSnappedObjectPosition(obj);
        }
    }
    //设置物体和手柄连接的位置 
    private voidSetSnappedObjectPosition(GameObject obj)
    {
        if (grabbedSnapHandle == null)
        {
            obj.transform.position =controllerAttachPoint.transform.position;
        }
        else
        {
            //设置旋转,controllerAttachPoint是手柄上的一个与物体的连接点
            obj.transform.rotation = controllerAttachPoint.transform.rotation *Quaternion.Euler(grabbedSnapHandle.transform.localEulerAngles);
            //因为grabbedSnapHandle和obj.transform之间可能不是同一个点，所以为了让手柄抓的位置是grabbedSnapHandle,需要减去括号中代表的向量
            obj.transform.position = controllerAttachPoint.transform.position - (grabbedSnapHandle.transform.position -obj.transform.position);
        }
    }
}