fix(viewnode): add optional ability to maintain node ordering

This change adds an argument to `addMissingNodes` to ensure that the
view node ordering is maintained. By default, ordering is not
maintained. However, for nodes of type `vtkActor2D`, where layering
requires a specific order, the node ordering is  enforced.

Author: sankhesh

Sources/Rendering/OpenGL/Renderer/index.js

@@ -24,16 +24,10 @@ function vtkOpenGLRenderer(publicAPI, model) {
       publicAPI.updateLights();
       publicAPI.prepareNodes();
       publicAPI.addMissingNode(model.renderable.getActiveCamera());
-      // Force all actor2D instances to be sorted and re-pushed as scenegraph nodes.
-      // This ensures that they are rendered in the correct order.
-      const actors2D = model.renderable.getActors2D();
-      actors2D.forEach((ac) => {
-        const vn = publicAPI.getViewNodeFor(ac);
-        if (vn !== undefined) {
-          publicAPI.removeNode(vn);
-        }
-      });
-      publicAPI.addMissingNodes(model.renderable.getViewPropsWithNestedProps());
+      publicAPI.addMissingNodes(
+        model.renderable.getViewPropsWithNestedProps(),
+        true
+      );
       publicAPI.removeUnusedNodes();
     }
   };

Sources/Rendering/SceneGraph/ViewNode/index.js

@@ -113,14 +113,27 @@ function vtkViewNode(publicAPI, model) {
 
   // add missing nodes/children for the passed in renderables. This should
   // be called only in between prepareNodes and removeUnusedNodes
-  publicAPI.addMissingNodes = (dataObjs) => {
+  publicAPI.addMissingNodes = (dataObjs, enforceOrder = false) => {
     if (!dataObjs || !dataObjs.length) {
       return;
     }
 
     for (let index = 0; index < dataObjs.length; ++index) {
       const dobj = dataObjs[index];
-      publicAPI.addMissingNode(dobj);
+      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;
+          }
+        }
+      }
     }
   };