Use page offset to calculate target coordinates

resources/js/game/GazePoint.js

@@ -9,14 +9,19 @@ class GazePoint {
 
   linkTo(node) {
     let bb = node.getBoundingClientRect(),
+      elementLeft = window.pageXOffset + bb.left,
+      elementTop = window.pageYOffset + bb.top,
+      elementRight = window.pageXOffset + bb.right,
+      elementBottom = window.pageYOffset + bb.bottom,
       coordinates;
-    if (this.screenX >= bb.left && this.screenX <= bb.right && this.screenY >=
-      bb.top && this.screenY <= bb.bottom) {
-      this.hasLink = true;
-      this.link = node;
-      this.targetX = this.screenX - bb.left;
-      this.targetY = this.screenY - bb.top;
-    }
+      if (this.screenX >= elementLeft && this.screenX <= elementRight && this
+        .screenY >=
+        elementTop && this.screenY <= elementBottom) {
+        this.hasLink = true;
+        this.link = node;
+        this.targetX = this.screenX - elementLeft;
+        this.targetY = this.screenY - elementTop;
+      }
     return coordinates;
   }