Quality and seeds
Substeps and the solvers' own step settings, what makes a bake come out the same every time, and seeds for another random take.
The same result, every time
A VecFlow bake is repeatable: the same file, baked again, gives the same frames, to the bit. That holds on another computer, on the CPU or an NVIDIA card, and however many cards share it, and when a bake carries on from a state save. So a look you approve on your computer is the look the render machine bakes.
The one exception is smoke on NVIDIA Flow, whose result depends on the card.
Seeds
Everything random in a simulation (where each particle is born, its spread, its variation) comes from its seed. Seed is in the Emission panel for a simulation on the sidebar's settings, and in the simulation's own panel for one with a flow (Seed).
Another number gives another random take on the same simulation: the same look, different details. Use it when one take has a clump or a gap you don't like. Two simulations with the same settings and seed come out the same, so give copies different seeds.
Substeps
Substeps in Bake Settings is how many steps the simulation takes each frame (2 by default). More steps follow fast things better:
- fast particles that go through thin colliders without hitting them;
- bounces and collisions that look soft or late;
- jittery piles and stacks.
Each substep costs about as much as the first, so 4 substeps is about twice the bake time of 2. Liquids and smoke also take extra substeps of their own when they move fast; see below.
Liquid and smoke steps
Liquids and smoke work out how many substeps they need from how fast they go, up to a limit:
- Smoke (VecFlow solver), in the Smoke and Fire panel: Step Size (the most cells the fastest gas may move in a substep; less is sharper and slower), Most Substeps, Most Rounds and Accuracy for the pressure solve. The defaults suit most shots.
- Liquids, on the flow's Liquid operator: Step Size (the share of the spacing the fastest particle may go in a substep), Most Rounds and Compression (how much it may be squeezed; less holds deep tanks flatter and steadier).
Lower these only if something looks wrong: a liquid that bounces or bulges, smoke that smears. Each is slower.
Detail
Detail is set by size, not by a quality switch:
- smoke by Cell Size: half the size is eight times the cells;
- liquids by the Liquid operator's Spacing: half the spacing is eight times the particles;
- a liquid's surface by Detail and Smoothness.
For quick looks, Draft halves the detail for you.