Assembly Decoration

Assembly Decoration places parts from an assembly library on a tree: branches, sprigs and leaf clusters that are already rigged, so they can bend with effectors and in the wind while staying instances. It is the main way to add foliage in Natsura. The library comes from an Assembly Resource, or from Rig to Assembly for parts you grew in Natsura. Assemblies covers the whole workflow.

Setting one up

Wire the library into the decoration's first input. With nothing wired it uses an example library, and if it reports no valid assemblies, check the pivots on the Assembly Resource.

A decoration does nothing until a Grow carries it. Select the Grows and choose Assembly Decoration from the toolbar's Decorate menu, or drag an existing Assembly Decoration into an empty slot under Decorations on the Grow. Until it is assigned, it previews on a built-in tree (trunk, monopodial or sympodial), picked with the Simulate selector on the display toolbar. Once a Grow carries it, the selector can show the real Simulate, and maps can read the tree's attributes.

Where parts spawn

Spawn at picks the points that get a part: Tips (the default), Intersections, Internodes and Roots, in any combination. With Internodes on, turn on Divisions to add points along each internode (1 adds the midpoint), or set Mode to Distance to space them by Step Length. Mode is greyed out until Internodes is on.

Mask is the chance that each point keeps its part. Map it to thin the crown by position, for example from u, so fewer parts spawn towards the inside. Group keeps only the library parts in a group, so the decoration picks from those.

Choosing parts with traits

When the library has more than one part, traits decide which part goes where. A trait is a value carried both by the tree's spawn points and by the library's parts, and each point takes the part whose values are closest. Traits explains the idea.

Add Selection Trait, in the Distribution folder, offers Create New for a trait of your own, or any attribute already on the skeleton, such as height or elevation angle. Most of the time you'll use skeleton attributes.

Press Enter with the decoration selected (or Launch) to open the chart beside the tree. The parts wait in a row below it. Drag parts onto the chart, and each point on the tree takes the part nearest its own values: with height on the X axis, put the small parts at the low end and the large ones at the high end, and the tree carries large parts up high and small ones lower down while the leaves stay the same size. Reset sends every part back off the chart. Traits covers the chart, the row menu and the rest of the trait controls.

Transform

Transform sets the scale and orientation of each part, and most of its values can be mapped. Parts are turned in a fixed order: Roll (Parent), Spiral, Whorl, Pitch, Yaw, Roll (Self), then Offset. Spiral Relative turns the parts once per internode, Absolute lines every part up the same way, and Skeleton keeps the frame the Grow made (the Spiral value is greyed out in Skeleton). Multiplicity places several parts at each point, spread by Whorl Angle.

If the parts were made at real size, leave Scale at 1. When they look too big for the tree, the tree usually needs more branching to carry them.

Effectors

The effector stack works as it does on the Grow, but it turns the joints of each part's rig, so parts bend and stay instances. Each effector row is set to Attract, Repel, Flatten, Align (up) or Level (up), weighted by a value or a map. With a plain value, the whole part turns. Map the weight from the part's own u, which runs from the part's base to its tips, and the bend changes along the part: a gravity effector can then droop only the tips. See Effectors.

Prune

Prune removes pieces where the crown is densest. It runs after placement and takes them out within each assembly rather than whole assemblies, so it thins the crown more naturally than Mask. The two work together. Prune can be mapped too, for example from elevation angle.

Export Rig

Export Rig passes each part's own rig into the tree's rig. Wind in Unreal can then move the smaller branches too, at the cost of many more joints, which Simplify Tree Rig and Skin can reduce.

Status

After Replace With on a trait row, the chart axis can keep the old trait; set the axis again from the row menu. Parts on the chart or in the viewport sometimes draw wrongly, and toggling the display flag fixes it.