Question by Mattorious · Jul 14, 2020 at 04:29 PM · ui math angles radial

Dragging a circle with mouse input into worldspace UI - Getting the correct angles

Howdy folks, I'm struggling with what should be a pretty simple math problem.

I'm essentially trying to create a system to drag a handle in a radial UI element that's positioned in world space. Hopefully, you can kinda see what I mean in this gif:

GIF

So, it's a bit hard to see in the gif, but the problem seems to be that every frame the angle flip flops between two angles on the circle. So, somewhere in the code the math is almost working, because I'm getting a passable result minus the flip-flopping in the positions. I'm thinking that there's maybe an extraneous calculation happening here every other frame causing the rotation to jump back somehow. But I can't find anything in the code that would cause that, so I'm kinda at a loss.

I'm using eulerangles here instead of quaternions cause they're easier to understand conceptually.

This is the code that calculates the angle I'm looking for based on the mouse input. I have a bad habit of not marking up code until I need to show it to someone, so it might be a bit confusing. If you have any questions please let me know.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.EventSystems;
 using UnityEngine.UI;
 
 public class RadialSlider: MonoBehaviour
 {
     //angle of dragged mouse drag input
     public float angle;
 
     //player controlled camera input
     public CameraMouseInput mouseInput;
 
     //ui element we're outputting angles to
     public DegreeIndicator dI;
 
     //checking if lclick is held down
     public ClickHeld cH;
 
     Camera mainCam;
     // mainloop
     public void Update()
     {
         mainCam = Camera.main;
         var input = FindObjectOfType<StandaloneInputModule>();
         
         if(input != null ) //if input exists
         {                
             if (cH.held) //if player is holding down lclick
             {
                 mouseInput.CanOrbit = false;                    
                 Vector2 localPos; // Mouse position  
                 
                 //Suspected problem with this line in particular
                 RectTransformUtility.ScreenPointToLocalPointInRectangle(GetComponent<RectTransform>(),  Input.mousePosition, mainCam, out localPos);
 
                 //localPos = Input.mousePosition;
                 // local pos is the mouse position.
                 angle = (Mathf.Atan2(-localPos.y, localPos.x) * 180f / Mathf.PI + 180f);
 
                 //assigning angle to UI indicator
                 dI.desiredAngle = (int)(angle);
                 
                 //currentValue = angle;
                 //Debug.Log(localPos+" : "+angle);    
             }
             else
                 mouseInput.CanOrbit = true;    
         }
         else
             UnityEngine.Debug.LogWarning( "Could not find GraphicRaycaster and/or StandaloneInputModule" );        
     }
 }

I've adapted the code from this wonderful person's work. Without them I probably wouldn't have gotten so far.

Thanks so much for any help! I appreciate all that you amazing people do for this community :)

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