Does Vector.Reflect really do reflect?

Unity Engine
,
1

Hi all. I found strange issue, may be there is mistake in official doc? Unity - Scripting API: Vector3.Reflect

My code is -

 Vector3 startPoint = transform.position;
        Vector3 secondPoint;
        RaycastHit hit;
        RaycastHit hit2;
        Vector3 rayDir = transform.forward;

        if (Physics.Raycast(startPoint, rayDir, out hit, 300))  //first line  blue
        {
               Debug.DrawLine(startPoint, hit.point, Color.blue);
               rayDir = Vector3.Reflect((hit.point-startPoint), hit.normal);
               secondPoint = hit.point;

              

               if (Physics.Raycast(secondPoint, rayDir, out hit2, 300)) 
               {    Debug.DrawLine(secondPoint, rayDir, Color.green);  // green line ???
                    Debug.DrawLine(secondPoint, hit2.point, Color.red); //second red line
               }
        }

the picture is -

705Ă—540 64.7 KB

May some one tell me why:

  1. Why green line is not a mirror at all (it uses Vector3.Reflect :frowning: ) ?
  2. Why the second red line doing exactly mirror effect?
2

Because you’re not passing in a point to draw to for the green line. You’re passing in a direction. If you want to draw a direction, you use Debug.DrawRay.

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3

Im totaly noob… thank you really. May be this example (with right code) should be placed to documentation?

4

There’s already two code examples for DrawLine and DrawRay. The arguments are described in both too.

You made a mistake is all. You actually use it correctly in several places (Lines 9 and 17) so I’m not sure I follow then why or how the docs should be changed?

1 Like
5

Yes you right, documentation about DrawRay and DrawLine is good. I mean documentation about “Vector3.Reflect” it only says only “Reflects a vector off the plane defined by a normal.” so why just don add at least some more about same " Debug.DrawLine(Point, point, Color) "; I see many question in old Unity Answers and forums about this makes people confuse. Just my advice to be more clear

6

The best way to be more clear is to always used named arguments whenever there is ambiguity, eg two Vector3 objects passed as arguments

For instance:

Always use named arguments with Physics.Raycast() because it contains many poorly-designed overloads:

https://discussions.unity.com/t/758115/8

7

I don’t quite understand what Debug.DrawLine has to do with Vector3.Reflect. Vector3.Reflect is a pure mathematical function. Essentially a basic vector math function. The line you quoted perfectly explains what it does. However there’s another paragraph which even goes more into details:

Maybe you have troubles understanding the difference between a position vector and a direction vector? The documentation of this method can not start teaching basic linear algebra :). If your linear algebra is a bit rusty, I can highly recommend the 3b1b series on linear algebra, at least the first few videos.

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