fix(vtkviewnode): fix addMissingNodes with enforceOrder

enforceOrder was forcing the dataObjs nodes to be the first children. That had the disadvantage to
make the OpenGLCamera the last item, and slow to be found. Instead, enforceOrder now simply enforce
that the created missing nodes are following each others.

fix #3497

Author: finetjul

Sources/Rendering/SceneGraph/ViewNode/index.js

@@ -12,6 +12,25 @@ function vtkViewNode(publicAPI, model) {
   // Set our className
   model.classHierarchy.push('vtkViewNode');
 
+  /**
+   * Convenient method to move a child to a specific index.
+   * @param {*} child the child to move
+   * @param {*} toIndex the index to move the child to
+   * @returns true if the child was moved, false otherwise
+   */
+  function moveChild(child, toIndex) {
+    for (let i = 0; i < model.children.length; ++i) {
+      // Start browsing from toIndex + 1
+      const childIndex = (toIndex + 1 + i) % model.children.length;
+      if (model.children[childIndex] === child) {
+        model.children[childIndex] = model.children[toIndex];
+        model.children[toIndex] = child;
+        return true;
+      }
+    }
+    return false;
+  }
+
   // Builds myself.
   publicAPI.build = (prepass) => {};
 
@@ -122,21 +141,19 @@ function vtkViewNode(publicAPI, model) {
       return;
     }
 
+    let nextIndex;
     for (let index = 0; index < dataObjs.length; ++index) {
       const dobj = dataObjs[index];
       const node = publicAPI.addMissingNode(dobj);
-      if (
-        enforceOrder &&
-        node !== undefined &&
-        model.children[index] !== node
-      ) {
-        for (let i = index + 1; i < model.children.length; ++i) {
-          if (model.children[i] === node) {
-            model.children.splice(i, 1);
-            model.children.splice(index, 0, node);
-            break;
-          }
+      if (enforceOrder && node !== undefined) {
+        if (nextIndex === undefined) {
+          // First node can be anywhere
+          nextIndex = model.children.lastIndexOf(node); // node is likely the list child
+        } else if (model.children[nextIndex] !== node) {
+          moveChild(model.children, node, nextIndex);
         }
+        // Next node must follow current node
+        nextIndex++;
       }
     }
   };