How to draw a gizmo on a Canvas ?

Question

Hi everyone. My problem is simple : I want to draw a line (using Gizmos.DrawLine()) on a Canvas. Do you know how to do that ?

Thanks for any answer ;)

Answer 1

Best Answer

Answer by aFeesh · Apr 17, 2020 at 04:48 PM

You need to change Gizmos.matrix to your Canvas's space. To do this get a reference to the transform of your Canvas root object, and use Transform.localToWorldMatrix

The code would like something like this:

 private void OnDrawGizmos()
 {
      Gizmos.matrix = m_CanvasTransform.localToWorldMatrix;
      Gizmos.DrawLine(m_Vector3From, m_Vector3To);
 }

This will draw a line in your Canvas's space via Gizmos.

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qsp18 · Mar 11, 2021 at 05:42 PM 0

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What exactly is: "m_CanvasTransform"? Some object in the canvas? The Canvas itself?

DaCookie qsp18 · Mar 12, 2021 at 02:23 PM 0

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Mh probably the Transform component on the Canvas :p

 private RectTransform m_CanvasTransform;

Answer 2

Answer by DaCookie · Mar 29, 2021 at 10:42 PM

Based on the answer of @aFeesh , and for anyone who find this post, I made an extension method to make our lives easier. This method will compute a matrix for drawing Gizmos on interfaces, by placing the (0; 0) point in the bottom-left corner of the Canvas.

 using UnityEngine;
 public static class CanvasExtensions
 {
     public static Matrix4x4 GetCanvasMatrix(this Canvas _Canvas)
     {
         RectTransform rectTr = _Canvas.transform as RectTransform;
         Matrix4x4 canvasMatrix = rectTr.localToWorldMatrix;
         canvasMatrix *= Matrix4x4.Translate(-rectTr.sizeDelta / 2);
         return canvasMatrix;
     }
 }

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How to draw a gizmo on a Canvas ?

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