Help with reflecting in 2D.

Question

I've been trying to create a little lasers and mirrors with the goal being get a laser past obstacles to a receiver and have been trying to get the reflecting down. To help I put a line gizmo to help me visualize things so i can just slap on a line renderer once I iron it out. I've been trying to do it recursively and i'm sure i'm close but i'm struggling to figure it out. Here is what i got:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class MyLaser3 : MonoBehaviour
 {
     public int maxReflectionCount = 5;
     public float maxStepDistance = 200;
 
     private void OnDrawGizmos()
     {
         drawPredictedReflection(this.transform.position, this.transform.up, maxReflectionCount);
     }
 
     void drawPredictedReflection(Vector2 position, Vector2 direction, int reflectionsRemaining)
     {
         if (reflectionsRemaining <= 0)
         {
             return;
         }
 
         Vector2 startingPos = position;
 
         RaycastHit2D hit2D = Physics2D.Raycast(startingPos, this.transform.up, maxStepDistance);
 
         if (hit2D) //if we hit somthing reflect, else just keep going
         {
             direction = Vector2.Reflect(direction, hit2D.normal);
             position = hit2D.point;
             Debug.Log(direction);
         }
         else
         {
             position += direction * maxStepDistance;
         }
 
         Gizmos.color = Color.yellow;
         Gizmos.DrawLine(startingPos, position);
 
         drawPredictedReflection(position, direction, reflectionsRemaining - 1);
 
 
     }
 }

Let me know your thoughts/improvements or if i'm way off and to try a different way.

Answer 1

Your math looks and ended up being fine. One issue you might've bumped into was your use of:

 position = hit2D.point;

for assigning the next ray source. This seems fine and it's right geometrically, but you end up with weird behavior from firing a new ray from the surface of a collider that it's also allowed to strike. You'll get a weird floating point situation where sometimes it will hit it and sometimes it won't.

In your case, you'd expect that you won't. To adjust for that, I added a portion of the next ray's direction to its starting position. This fixed the clipping issue and got the expected behavior:

alt text

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class RayReflect : MonoBehaviour
 {
     public int maxReflectionCount = 5;
     public float maxStepDistance = 200;
 
     void OnDrawGizmos()
     {
         if (!Application.isPlaying)
             return;
 
         var source = this.transform.position;
         var xyPlane = new Plane(Vector3.forward, source);
 
         var cameraRay = Camera.main.ScreenPointToRay(Input.mousePosition);
 
         if (xyPlane.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out float enter))
         {
             var worldCursor = cameraRay.GetPoint(enter);
             var direction = (worldCursor - source).normalized;
 
             this.DrawPredictedReflection(source, direction, this.maxReflectionCount);
         }
     }
 
     void DrawPredictedReflection (Vector2 position, Vector2 direction, int reflectionsRemaining)
     {
         var gizmoHue = (reflectionsRemaining / (this.maxReflectionCount + 1f);
         Gizmos.color = Color.HSVToRGB(gizmoHue, 1, 1);
 
         RaycastHit2D hit2D = Physics2D.Raycast (position, direction, maxStepDistance);
 
         if (hit2D && hit2D.collider) //if we hit somthing reflect, else just keep going
         {
             Gizmos.DrawLine (position, hit2D.point);
             Gizmos.DrawWireSphere(hit2D.point, 0.25f);
 
             direction = Vector2.Reflect (direction, hit2D.normal);
             position = hit2D.point + direction * 0.01f;
         }
         else
         {
             Gizmos.DrawLine (position, position + direction * maxStepDistance);
             position += direction * maxStepDistance;
         }
 
         Gizmos.color = Color.white;
 
         if (reflectionsRemaining > 0)
             DrawPredictedReflection (position, direction, --reflectionsRemaining);
     }
 }

Help with reflecting in 2D.

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