Welcome to Simstim
Jack into someone else's hours in the viewport. Notes, tutorials and fast references for TDs across Houdini, Unreal, Blender and Rhino.
It's 2 a.m. and the farm is chewing through a sim that will explode at frame 212. You know it will explode because it exploded last night, and the night before that. Somewhere in the documentation is the one flag that stops it. You have nine tabs open. Four are forum threads from another decade. One answers a different question. The review is at ten.
Simstim is built for that hour.
Jacking in
In William Gibson's Sprawl, simstim is a feed of somebody else's senses. You jack in and you ride their nervous system: their eyes, their hands, their hours. You get the experience without paying what it cost.
That's the deal here. Every post on this site is someone else's hours in the viewport, with the dead ends, the crashed builds and the flag nobody wrote down, compressed into something you can run before your coffee goes cold.
What's on the wire
Simstim covers the four applications most technical directors end up living between:
- Houdini: VEX, wrangles, Python (
hou), simulation and USD. - Unreal: editor scripting, Python, PCG, and the pipeline glue between Unreal and everything else.
- Blender:
bpy, Geometry Nodes, and batch work from the command line. - Rhino: RhinoCommon, Python 3 and Grasshopper.
Posts come in two kinds. News is sourced and dated, and it tells you why a release matters to someone who builds tools, not someone who reads press releases. Tutorials are code you can paste. Where we can run the code, we run it before it ships and tell you the exact version it ran on. Where we can't, we say so at the top, in plain words. No silent guesses.
The reference
The first reference is the VEX Dictionary: all 1,118 VEX functions in Houdini 22, searchable as you type. Signatures come straight from the compiler, not from memory. Every summary is written in our own words and fact-checked against the signatures and SideFX's documentation before it goes live. A first handful of the most-used functions have worked examples you can drop into a wrangle, and more arrive with every post. Mention a function in a post, like pcopen or xyzdist, and it links straight to its entry.
The dictionary is the template. Houdini Python, bpy, Unreal's unreal module and RhinoCommon are next, built the same way: fast to search, written plainly, checked before they ship.
Why speed matters
The official docs are good. They're also a city: vast, accurate, and easy to get lost in after midnight. Mid-shot, you don't want the city. You want one street, one door, and the one line of code behind it.
Simstim is a map of the doors.
Plug in
- Browse by application from the menu: Houdini, Unreal, Blender, Rhino.
- Search the VEX Dictionary. On the home page or in the dictionary, press
/to jump straight to the search box. - Follow the Atom feed, or find us on daily.dev, and new posts come to you.
Spot a wrong signature, a broken example, a claim that doesn't hold? Tell us. A reference is only as good as the last error somebody reported.
See you on the other side of the screen.
Related
HoudiniStage in, stage out: Houdini's Solaris treats every node as a function over a USD sceneIn Houdini's Solaris, every LOP node takes a composed USD stage and returns one, and its edits land in one in-memory layer at the top. A 31-line usd-core model of that contract, the Python LOP that does it for real, the same network checked in Houdini 22, and why a Layer Break decides what gets saved.
Houdinisplit() is a tokenizer: building cache paths from strings in Houdini VEXVEX strings look like Python's, but split() merges separators and drops empty fields, len() counts bytes, and a wrangle expands $ before the compiler sees it. A per-piece cache path built from the scene file name, and the traps along the way, checked in Houdini 22.
HoudiniOut of range returns 0: arrays and array attributes in Houdini VEXVEX arrays slice like Python lists, but an out-of-range read quietly returns 0, a write past the end grows the array, and arrays can't nest. Per-point neighbor lists sorted by distance, read back from other points, and the traps that turn a bad index into point 0.