這裡要用到一個攝像機函式Camera.ViewportToWorldPoint, Unity官方對其定義為：
Camera.ViewportToWorldPoint 視窗轉世界位置
function ViewportToWorldPoint (position : Vector3) : Vector3

Description描述

Transforms position from viewport space into world space.

從視窗空間到世界空間的變換位置。

Viewport space is normalized and relative to the camera. The bottom-left of the camera is (0,0); the top-right is (1,1). The z position is in world units from the camera.

視口空間是歸一化的並相對於相機的，相機的左下為（0,0）；右上是（1,1）；Z的位置是以世界單位衡量的到相機的距離。

Note that it transforms a x-y screen position, into a x-y-z position in 3D space.

請注意它是變換一個x-y螢幕位置到一個3D空間的x-y-z位置。

You provide the function with a vector where the x-y components of the vector are the screen coordinates and the z component is the distance of the resulting plane from the camera.

這個函式帶有在螢幕座標的x-y元件向量，並且z元件是在從相機產生的平面的距離。

看了官方文件，現在我們知道怎麼獲取螢幕的實際寬高，下面是示例程式碼：

    private float width;
    private float height;

    void SetBasicValues(){

        float leftBorder;
        float rightBorder;
        float topBorder;
        float downBorder;
        //the up right corner
        Vector3 cornerPos=Camera.main
 
.ViewportToWorldPoint(new Vector3(1f,1f,Mathf.Abs(Camera.main.transform.position.z)));

        leftBorder=Camera.main.transform.position.x-(cornerPos.x-Camera.main.transform.position.x);
        rightBorder=cornerPos.x;
        topBorder=cornerPos.y;
        downBorder=Camera.main.transform.position.y-(cornerPos.y-Camera.main.transform.position.y);

        width=rightBorder-leftBorder;
        height=topBorder-downBorder;
    }

得到的width與height就是螢幕寬高，程式碼的含義上面已經說的很清楚了。