Simulate

Simulate is the end point of every Natsura graph. The Grows, switches, maps, effectors and decorations wired into it describe the tree; Simulate runs that description step by step and produces the tree with its skin and rig. Nothing grows without one. Simulation covers what happens inside.

Placing a Simulate from the Natsura toolbar at object level creates a geometry container called Natsura and takes you inside it, where most Natsura work happens.

Inputs

• Graph takes the recipe: the trunk Grow and everything wired into it.
• Source takes points to grow from. They can be a scatter for a forest (Seed Points makes one) or points from an earlier Simulate to grow a new simulation on top of. Each point's seed and width are read by default (Seed Attribute and Width Attribute), and Source Points limits growth to a group. Any other attribute on the points keeps its name and is carried into the tree grown from it; see Attributes.
• Geometry takes a polygon environment for the tree to respond to. Growth collides with its objects, and the tree gets a direction towards the light (phototropism_direction), which steers growth only where a Grow has Photo Direction in an effector row.

Output

Simulate has a single output since 0.7.2. One wire carries the tree and its rig into Simplify Tree Rig and Skin, Rig to Assembly, Wind Config and Export Unreal Nanite Assembly. In scenes from before 0.7.2, anything wired to the old second (rig) output, including nodes of your own, needs reconnecting by hand.

Globals

Most of the time the settings you change here are Global Seed and posing.

Simulation Mode is Autocomplete by default, which shows the tree fully grown. Generation Slider ties growth to Generation, which follows the timeline unless you change it, so you can scrub through the tree's life step by step and pose it partway.

Global Seed changes the randomness across the whole tree, or the whole forest. Random picks the random number scheme: 2 (current) for everything made since 0.6.1, and 1 (legacy) for older scenes, which open on 1 so their trees branch as they did.

Postprocess

Enable Postprocess (on by default) refines the grown shape before the decorations run, so every decoration and every placed assembly follows the same refined branches. It has its own effector stack, Substep Effectors. Scenes from 0.6 open with it off, as it was then.

Posing

Simulate has an interactive state in the viewport for posing the tree by hand. With the Generation Slider you can stop at any step, change a branch's orientation, and let the tree carry on growing from there, so a small change early on can lead somewhere different.

Poses are stored against joint names, so they survive a re-simulation as long as the joints keep their names. If joints disappear, poses can go missing or land on a different part of the tree, and a new seed can make them meaningless. Work additively: cutting parts of the tree after posing can lose poses. The clear current, clear forwards and clear all buttons at the top of the parameters remove the current edit, the edits on later generations, or all of them. See Interactive tools.

Display

Output Mode switches what you see: Decorated is the full meshed tree, Preview a lightweight shaded version, and Skeleton the growth curves only, which is fastest to work with. With the Natsura UI on, the Output menu on the display toolbar, which sits above the parameter pane, sets the same thing (Meshed, Shaded, Skeleton). The toolbar's Wind selector (Calm, Breeze, Strong) sets the scene's Wind Environment, which the wind preview follows (see Wind). Human and Yardstick show a figure and a yardstick for scale.

Advanced

The advanced settings can stay on their defaults. Width Mode should stay on Standard Width, which takes width from the growth nodes. Incoming Environment is Precalculated speeds up simulations with a prepared environment.

Recooking on every drag

Every slider drag on a growth node recomputes the tree. Setting Houdini's update mode (bottom right) to On Mouse Up only updates the viewport when you let go.

Status

The fourth input, Objects, isn't used in 0.7.3, so leave it empty. Postprocess, and the Postprocess Stack under Advanced, are experimental. Enable Deflection is experimental and best left off. Bucket Size is for tiled simulation, which isn't ready for production. The Gather Strands width modes are deprecated, and the width model is being reworked.