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Simplify Tree Rig and Skin

Simplify Tree Rig and Skin cuts a tree's joint count down to what the engine can afford and rebinds the skin, before wind and export.

Every tree that comes out of a Simulate is rigged and skinned, with joints all along its branches. That is more joints than a game engine needs. Simplify Tree Rig and Skin removes joints and rebinds the skin to the ones that are left, so you decide how much rig you can afford.

It goes straight after the Simulate, before your Wind Config layers and Export Unreal Nanite Assembly. Simplify before setting up wind, so the layers are built on the joints that get exported. The tool is on the Natsura toolbar under Rig & Export.

Settings

Each reduction has a toggle beside it, and its value is greyed out until the toggle is on.

  • Carve (on by default) trims joints off the ends of the branches, up to this distance from the tips. At 0 it removes nothing.
  • Minimum Length (off by default) removes branches shorter than this length.
  • Skeleton Simplification (on by default) removes joints that add little to a branch's shape, with Simplify as the tolerance.
  • Max Joints (off by default, 500 when on) caps the joint count, keeping the joints on the longest branches. 500 to 600 is a good number for a tree.
  • Remove Unused Joints (off by default) removes joints that nothing is bound to.

Remove Unused Joints needs the component_name attribute that Simulate writes on the mesh. If it's missing, the node shows a warning.

If the tree's parts bring their own rigs through an Assembly Decoration (its Export Rig setting), the joint count goes up a lot. That gives finer wind in Unreal, at the cost of many more bones, so simplify with that in mind.

Checking the rig

The Debug folder switches what the node displays: mesh, bonecapture, joints and skeleton. Turn off mesh to see the joints that are left. Turn on bonecapture to check the skinning: if you see lines running out across the tree, points are bound to the wrong joints and the rig is bad. See Debug Tree Rig.

For joint and instance counts, put an Assembly Inspect after the node.

Status

The wind preview can stop after Simplify Tree Rig and Skin; restarting Houdini may fix it.

Signal

Signal turns ordinary Houdini geometry into an input the growth graph can read, for growth that responds to its surroundings. A Wrangle does this for you on its extra inputs.

Simulate

Simulate runs the growth recipe built from Grow, Split, Switch and the other growth nodes, and outputs the finished tree with its rig on a single output.