title: How to find the coordinates of a click in the Babylon.js scene?
body: <p>I'm starting in Babylon not long ago, I'm looking for some way to find the coordinates of mouse when there is a click on the canvas. I was able to easily find this for a given object, but not for the scene itself (!?) I do not know what could be wrong, it seems silly, but I have not found the solution... </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>window.addEventListener('DOMContentLoaded', function () {
      var canvas = document.getElementById('canvas');
      var engine = new BABYLON.Engine(canvas, true); 
              
      var createScene = function () {
          var scene = new BABYLON.Scene(engine);
          scene.clearColor = new BABYLON.Color3.White();
  
          var box = BABYLON.Mesh.CreateBox("Box",4.0,scene);
          var camera = new BABYLON.ArcRotateCamera("arcCam",
                       BABYLON.Tools.ToRadians(45),
                       BABYLON.Tools.ToRadians(45),
                       10.0,box.position,scene);
                       camera.attachControl(canvas,true);
  
          var light = new BABYLON.PointLight("pointLight",new BABYLON.Vector3(
              0,10,0),scene);
          light.diffuse = new BABYLON.Color3(1,1,1);
  
          var onpickAction = new BABYLON.ExecuteCodeAction(
          BABYLON.ActionManager.OnPickTrigger,
          function(evt) {
              console.log("(",evt.pointerX,",",evt.pointerY,")");  
          });
  
          //doesn't work (???)
          scene.actionManager = new BABYLON.ActionManager(scene);
          scene.actionManager.registerAction(onpickAction);
  
          //works fine
          box.actionManager = new BABYLON.ActionManager(scene);
          box.actionManager.registerAction(onpickAction);
  
          return scene;
      }
  
      var scene = createScene();
      engine.runRenderLoop(function () {
          scene.render();
      });
   });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html lang="en"&gt;
  &lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Title&lt;/title&gt;
      &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/babylonjs/2.5.0/babylon.js"&gt;&lt;/script&gt;
      &lt;style&gt;
          #canvas {
              width: 100%;
              height: 100%;
          }
      &lt;/style&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;canvas id="canvas"&gt;&lt;/canvas&gt;
  &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>