and why do we still need Xpresso?

Scene Nodes have two main areas of application.

One is the generation of geometry, the other is the modification of it.

There are other aspects to it that were showcased in the Tech Demo state of Scene Nodes, but those have become part of the experimental side of Scene Nodes in Cinema 4D 2024.

Scene Nodes allow the creation of own primitives that are either based on an algorithm, think any of the common parametric objects or of course your own creation.

They can also use existing objects as input for geometry generation, i.e. you can use Scene Nodes to create Splines from the edges of a polygon object.

This makes them similar to the known generators as well.

The other aspect of Scene Nodes is the modification of existing geometry, be it as deformers or as modifiers that actually change the topology of objects.

The modification of geometry doesn’t stop at modeling functions, you can also create and adjust any kind of geometry related data like selections, weight maps, normal maps etc.

And this is maybe the key fundamental difference to Xpresso. Where Scene Nodes give basically unlimited access to geometry modifications, Xpresso only allows for the control of parameters. They work in very different contexts within Cinema 4D and their functionality is not interchangeable. Scene Nodes can easily subdivide a cube, but they can’t change the subdivision parameters of a cube, for Xpresso it is the reverse.