Gets the viewport rectangle cameras at different distances

using UnityEngine;
using System.Collections;
 
public class CameraView : MonoBehaviour {
    
    
    private Camera theCamera;
 
        //距离摄像机8.5米 用黄色表示
    public float upperDistance = 8.5f;
    //距离摄像机12米 用红色表示
    public float lowerDistance = 12.0f;
    
    private Transform tx;
    
    
    void  Start (){
        if ( !theCamera )
        {
            theCamera = Camera.main;
        }
        tx = theCamera.transform;
    }
    
    
    void  Update (){
        FindUpperCorners();
        FindLowerCorners();
    }
    
    
    void  FindUpperCorners (){
        Vector3[] corners = GetCorners( upperDistance );
        
        // for debugging
        Debug.DrawLine( corners[0], corners[1], Color.yellow ); // UpperLeft -> UpperRight
        Debug.DrawLine( corners[1], corners[3], Color.yellow ); // UpperRight -> LowerRight
        Debug.DrawLine( corners[3], corners[2], Color.yellow ); // LowerRight -> LowerLeft
        Debug.DrawLine( corners[2], corners[0], Color.yellow ); // LowerLeft -> UpperLeft
    }
    
    
    void  FindLowerCorners (){
        Vector3[] corners = GetCorners( lowerDistance );
        
        // for debugging
        Debug.DrawLine( corners[0], corners[1], Color.red );
        Debug.DrawLine( corners[1], corners[3], Color.red );
        Debug.DrawLine( corners[3], corners[2], Color.red );
        Debug.DrawLine( corners[2], corners[0], Color.red );
    }
    
    
    Vector3[] GetCorners (  float distance   ){
        Vector3[] corners = new Vector3[ 4 ];
        
        float halfFOV = ( theCamera.fieldOfView * 0.5f ) * Mathf.Deg2Rad;
        float aspect = theCamera.aspect;
        
        float height = distance * Mathf.Tan( halfFOV );
        float width = height * aspect;
        
        // UpperLeft
        corners[ 0 ] = tx.position - ( tx.right * width );
        corners[ 0 ] += tx.up * height;
        corners[ 0 ] += tx.forward * distance;
        
        // UpperRight
        corners[ 1 ] = tx.position + ( tx.right * width );
        corners[ 1 ] += tx.up * height;
        corners[ 1 ] += tx.forward * distance;
        
        // LowerLeft
        corners[ 2 ] = tx.position - ( tx.right * width );
        corners[ 2 ] -= tx.up * height;
        corners[ 2 ] += tx.forward * distance;
        
        // LowerRight
        corners[ 3 ] = tx.position + ( tx.right * width );
        corners[ 3 ] -= tx.up * height;
        corners[ 3 ] += tx.forward * distance;
        
        return corners;
    }
}