Fix: occasional incorrect tree order in getChildrenAtPosition

src/tree/Stage.mjs

@@ -22,6 +22,7 @@
  */
 
 import EventEmitter from "../EventEmitter.mjs";
+import ElementCore from "./core/ElementCore.mjs";
 import Utils from "./Utils.mjs";
 import WebGLRenderer from "../renderer/webgl/WebGLRenderer.mjs";
 import C2dRenderer from "../renderer/c2d/C2dRenderer.mjs";
@@ -543,9 +544,11 @@ export default class Stage extends EventEmitter {
 
     getChildrenByPosition(x, y) {
         const children = [];
-        this.root.core.update();
+        this.ctx.updateTreeOrder = 0;
+        this.root.core.updateTreeOrder();
         this.root.core.collectAtCoord(x, y, children);
 
+        children.sort(ElementCore.sortZIndexedChildren);
         return children;
     }
 }

src/tree/core/CoreContext.d.mts

@@ -25,6 +25,7 @@ export default class CoreContext {
   stage: Stage;
 
   renderToTextureCount: number;
+  updateTreeOrder: number;
 
   constructor(stage: Stage);
 

src/tree/core/ElementCore.d.mts

@@ -121,6 +121,8 @@ declare class ElementCore {
   /**
    * Fill the array `children` with all the ElementCore instances (including itself and
    * its children) that intersect the point (`x`, `y`)
+   * 
+   * To enforce z-sorting, the result should be sorted using `ElementCore.sortZIndexedChildren`.
    *
    * @param x
    * @param y

src/tree/core/ElementCore.mjs

@@ -2032,8 +2032,8 @@ export default class ElementCore {
                 }
             } else {
                 a.splice(n); // Remove items that were sorted in b array, so that we can sort a
-+               // Beware that the function passed here to Array.sort must be stable
-+               a.sort(ElementCore.sortZIndexedChildren); // Needed because items with same _zIndex may not be ordered by _updateTreeOrder
+                // Beware that the function passed here to Array.sort must be stable
+                a.sort(ElementCore.sortZIndexedChildren); // Needed because items with same _zIndex may not be ordered by _updateTreeOrder
                 // Merge-sort arrays;
                 ptr = 0;
                 let i = 0;
@@ -2163,8 +2163,6 @@ export default class ElementCore {
                 this._children[i].collectAtCoord(x, y, children);
             }
         }
-
-        return children.sort(ElementCore.sortZIndexedChildren);
     }
 
     inBound(tx, ty) {