Using a variable from Start for Update

Henlo, i'm fairly new to C# and Unity and was trying to scale my background along with the Canvas without using anchor point and breaking the pixel (stretching, etc)

I figured out a basic formula that will help me solve the task by scaling the renderTexture .
By dividing the "new" RectTransform in Update , with "old" RectTransform in Start , in my case it was 3840 / 1920 = 2 (3840 is default resolution *Start* and 1920 after i changed the resolution *UPDATE*)
I then will use the "result" for the scaling, thus matching the canvas size .

It works in theory and manual adjustment, but i can't get the code to work for automation .
the code did compile but Unity editor gave out an error "
NullReferenceException: Object reference not set to an instance of an object
MenuBackgroundScaler.Update () (at Assets/Scripts/MainMenu/MenuBackgroundScaler.cs:45)
".
I understand that this error is referencing to a null/empty variable .
"oldrt" to be exact .

I think the problem comes down to me not knowing how to use a result from Start and bring it to Update

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using TMPro;
5.  
6. public class MenuBackgroundScaler : MonoBehaviour
7. {
8.  
9.     public Canvas canvas;
10.     public GameObject menubackground;
11.  
12.     private RectTransform oldrt;
13.    
14.     void Start()
15.     {
16.         //Fetch the RectTransform from the GameObject
17.      
18.         canvas = gameObject.GetComponent<Canvas>();
19.         Debug.Log (canvas.enabled);
20.  
21.         //old canvas size
22.         RectTransform oldrt = canvas.GetComponent<RectTransform>();
23.      
24.         oldrt.sizeDelta = new Vector2(oldrt.sizeDelta.x, oldrt.sizeDelta.y);
25.      
26.     }
27.  
28.     void Update()
29.     {
30.         //getting the rect values
31.  
32.         RectTransform rt = canvas.GetComponent<RectTransform>();
33.  
34.         //formula
35.  
36.  
37.         if (rt.sizeDelta == new Vector2(3840f, 2160f) || rt.sizeDelta == new Vector2(5120f, 2160f))
38.  
39.         {
40.             menubackground.transform.localScale = new Vector3(oldrt.sizeDelta.x/rt.sizeDelta.x, oldrt.sizeDelta.x / rt.sizeDelta.x, oldrt.sizeDelta.x / rt.sizeDelta.x);
41.         }
42.         else
43.         {
44.             menubackground.transform.localScale = new Vector3(0.5f, 0.5f, 0.5f);
45.         }
46.     }
47. }
48.  

Note: i could just put in the actual result, but doing so mean i will have to manually calculate for all the different resolution, plus i'm still in the process of learning, so knowing how to get this to work would be nice, please help

 

The end result you've already got's quite good actually, I don't think you need to worry too much

 

but how can i bring the oldrt variable from Start to Update , the code did compile but Unity gave out a null error, meaning the result of oldrt variable didn't transfer from Start to Update at all

 

In Start, change

RectTransform oldrt =

to

oldrt =

. You're redeclaring it otherwise.. so the value is assigned to the new one in the function, instead of the one you've declaring outside of the function (which Update will be using).

 

Thanks you very much !!! it works like charm , now my background is scaling with every different resolution setup, no need to manually calculate it anymore !

 

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using TMPro;
5. public class MenuBackgroundScaler : MonoBehaviour
6. {
7.     public Canvas canvas;
8.  
9.     public GameObject menubackground;
10.     private RectTransform oldrt;
11.     private RectTransform newrt;
12.     private float oldx;
13.  
14.     private void Awake()
15.     {
16.  
17.     }
18.     void Start()
19.     {
20.         //Fetch the RectTransform from the GameObject
21.         canvas = gameObject.GetComponent<Canvas>();
22.         Debug.Log(canvas.enabled);
23.         //old canvas size
24.         oldrt = canvas.GetComponent<RectTransform>();
25.         oldrt.sizeDelta = new Vector2(oldrt.sizeDelta.x, oldrt.sizeDelta.y);
26.         Debug.Log("oldrt value" + oldrt.sizeDelta.x);
27.         //transfer result of oldrt to oldx
28.         oldx = oldrt.sizeDelta.x;
29.         Debug.Log("oldx" + oldx);
30.     }
31.     void Update()
32.     {
33.         //getting the rect values and scaling
34.        AutomaticSetScale();
35.     }
36.     private void AutomaticSetScale()
37.     {
38.        float newvalue;
39.    
40.         newrt = canvas.GetComponent<RectTransform>();
41.         newrt.sizeDelta = new Vector2(newrt.sizeDelta.x, newrt.sizeDelta.y);
42.         newvalue = newrt.sizeDelta.x / oldx;
43.  
44.         Debug.Log("rt value" + newrt.sizeDelta.x);
45.         if (newrt.sizeDelta == new Vector2(1920f, 1080f) || newrt.sizeDelta == new Vector2(2560f, 1080f))
46.         {
47.             //background native is 4K ( 5120 x 2160) scale it to 0.5f for 1080p
48.             menubackground.transform.localScale = new Vector3(0.5f, 0.5f, 0.5f);
49.         }
50.         else
51.         {
52.             //scaling value
53.             //formula
54.             /*By dividing the "new" RectTransform in Update , with "old" RectTransform in Start , example 3840 / 1920 = 2 (3840 is default resolution *Start* and 1920 after changed the resolution *UPDATE*)
55.             .*/
56.        
57.             menubackground.transform.localScale = new Vector3(0.5f * newvalue, 0.5f * newvalue, 0.5f * newvalue);
58.             Debug.Log("newvalue =" + newvalue);
59.         }
60.     }
61. }