Object Nodes

Objects are without doubt the most ubiquitous containers of data in Blender. The storage and processes for generating data in objects are very incoherent:

  • Direct attributes: obmat, parenting, visibility, layers, BGE settings, ...

    (most ancient features)

  • Optional pointers: Pose data, Proxy links, Sculpt data, Softbody, …

  • Lists/Stacks: Modifiers, Constraints, Particle Systems, ...

Stack-based process descriptions are generally inflexible. While parts can be combined and reordered, the individual parts themselves are usually quite complex and hard-coded. Adding or extending functionality leads to “feature creep”: The only way to express new behavior is to add more buttons, and one ends up with overstuffed and incomprehensible panels. More features in turn cause incompatible settings and broken corner cases.

Nodes promise to avoid these problems:

  • Sockets and explicit connections allow reusing components beyond simple chains
  • Node groups help to organize sets of nodes behind a custom interface
  • Basic nodes can become small and concise, larger features work like node groups
  • Artists can start with a clean slate or a minimal default setup, then just add what is needed
  • Small-scale nodes enforce stateless code without side-effects

Components

Many modifiers currently store various kinds of persistent data, for example particle state, voxel data, or mesh binding weights. The mingling of data and processing here makes it difficult to reuse modifier setups, because the data stored in them is specific to just one object.

Nodes are already maintained in a separate datablock (“Node Tree” ID datablocks). So using nodes instead of stacks for processing object data implies separating them from the data. Nodes themselves should be state-less (not store persistent data), so that they can be used in multiple contexts. All the data they work on is provided by input arguments.

That leaves objects with largely “passive” data storage, tentatively called “components” to avoid confusion. Components can be regarded as the data part of modifiers.

Todo

access to components in nodes, separate data storage into “scene database”/cache/renderer -> components are just formal descriptors

User Choice: Nodes vs. Stacks

For simple workflows and for the sake of familiarity, the use of traditional modifier- or constraint stacks may be preferable. To make the transition as smooth as possible, most existing object functionality could be supported both ways. This is comparable to how shaders have a Use Nodes option already, which toggles between a simple setup from panel buttons and a fully-fledged node setup.

For object nodes the combination of nodes and a classic button UI is more involved, because of the multitude of different features affected. A complete and detailed solution is out of scope in this proposal, but a rough sketch shall be attempted.

Todo

nodes as part of stacks vs. stacks as part of nodes, depsgraph as framework

Workflow Case Studies

Note

The workflow case studies in this proposal usually focus on high-level node setups for typical basic tasks. Most of the nodes in these examples would be composites of smaller building blocks. That means a user can make a new variant of a feature by using them like node groups:

  1. copy the node type (like copying the group datablock, rather than a single node)
  2. “open” (= edit) the internal nodes
  3. tweak the input/output sockets if necessary

This gives a great deal of flexibility without the need to pre-define each and every potential use case. Blender would provide the basic presets as described here, and these can be sufficient as-is in many cases. But extending the range of node types for specialized purposes should be a perfectly acceptable way of using nodes (compared to the cumbersome node group management we have now).

Simple Animation Workflow

Note

linking issues are ignored here, everything assumed to be local, no proxies needed!

  1. By default the mesh component (Mesh object data block) is used as render output directly.
_images/animation_workflow_base1.png
  1. Armature node deforms the mesh using the Armature object. The Armature object has a pose component. Note that the armature object is not connected to a render node or viewport node, so it will just display bone poses by default. .. note:: Proxies would override this pose component, even though it is locked when using a linked object.
_images/animation_workflow_base2.png
  1. Rigging workflow can also happen with nodes: The Armature object’s “Pose” component contains a node network representing bone constraints.

Todo

It’s unclear how this should work in detail. The ‘Bone Constraints’ node is like a group containing individual constraints.

_images/animation_workflow_base3.png
  1. Animate!
Moving bones in pose mode changes pose bone transforms (in the “Pose” component). Keyframes are stored in the Armature object’s animation data.
_images/animation_workflow_base4.png