Assembly Resource

Assembly Resource turns a kit of parts (branches, sprigs, leaves, buds) into an assembly library. It imports the kit, checks the pivots, rigs every assembly automatically, assigns materials, and previews the result in the wind. Its output goes into an Assembly Decoration. In Natsura a resource is an input that is already set up for the system; Surface Resource is another. Place one from the toolbar's Assemblies menu. Assemblies covers the whole workflow.

The kit

Wire geometry into the first input, or leave it empty and load a file: Filetype is USD or BGEO, and the BGEO default is an example branch kit. Pieces names the attribute that marks instances of the same geometry, which share a name. Uniform Scale and Rotate bring a kit from another program to the size and orientation of your tree.

The parts are packed instances, and each one's pivot sits at its base, where it joins its parent: a branch where it meets the trunk or a larger branch, a leaf or bud where it meets its stem. Rigging works out what attaches to what from these pivots.

Pivots

Parts with bad pivots show red, and the viewport asks you to fix them. Press Enter to open the pivot state, which shows only the parts. Left-drag over a part from its base in the direction it points to place its pivot, then fine-tune with the gizmo where you need to; the drag doesn't handle concave shapes well, so use the gizmo there. When every pivot is valid the warning goes, and the node shows how many instances and assemblies it found. Pivot Edit has the same state.

Checking the rig

Play the timeline: the library moves in the preview wind, set with the Wind menu on the display toolbar (Calm, Breeze, Strong). If no parts come loose, the rigging worked. Display Rig shows the joints and Display Pivots the pivots, and Colour shades the parts by u, assembly or instance. This wind is only a check on the rig, not a preview of how the tree will move in Unreal.

Materials

Each row under Materials assigns a Surface Resource to a group of faces; drag the Surface Resource node onto the row's field. Leave Group empty for the whole kit, or pick a group. Any Houdini group syntax works, and the shape groups (cardish, tubeish, needleish, blobish) are a quick guess from each piece's shape: needles and short twigs can swap, and double-sided leaves can read as tubeish, so check the result in the viewport. Add rows for a kit with several materials, such as bark and leaves.

Editing after rigging

The buttons at the top of the parameters switch between the states: Edit Pivot for pivots, Edit Assembly to turn parts or their joints after rigging, and Default to leave both. Edit Assembly works as on Assembly Edit, for example to turn parts that face a different way from the rest of the library.

Inside

Assembly Resource runs Import Assembly, Partition Assemblies, Pivot Edit, Build Assembly Rig (which runs Assembly Pack inside), Assembly Edit and Visualize Assemblies, in that order. Import Assembly, Pivot Edit and Assembly Edit are also in the Tab menu, but Partition Assemblies and Build Assembly Rig are hidden, so use the Assembly Resource to rig a kit. See Internal nodes.