unity3d 获取相机视口四个角的坐标

功能：如标题所示，主要考虑用来做3d Plane的自适应屏幕

/// <summary>
    /// 获取指定距离下相机视口四个角的坐标
    /// </summary>
    /// <param name="cam"></param>
    /// <param name="distance">相对于相机的距离</param>
    /// <returns></returns>
    public static Vector3[] GetCameraFovPositionByDistance(this Camera cam, float distance)
    {
        Vector3[] corners = new Vector3[];

        float halfFOV = (cam.fieldOfView * 0.5f) * Mathf.Deg2Rad;
        float aspect = cam.aspect;

        float height = distance * Mathf.Tan(halfFOV);
        float width = height * aspect;

        Transform tx = cam.transform;

        // 左上角
        corners[] = tx.position - (tx.right * width);
        corners[] += tx.up * height;
        corners[] += tx.forward * distance;

        // 右上角
        corners[] = tx.position + (tx.right * width);
        corners[] += tx.up * height;
        corners[] += tx.forward * distance;

        // 左下角
        corners[] = tx.position - (tx.right * width);
        corners[] -= tx.up * height;
        corners[] += tx.forward * distance;

        // 右下角
        corners[] = tx.position + (tx.right * width);
        corners[] -= tx.up * height;
        corners[] += tx.forward * distance;

        return corners;
    }