Performance
What makes a bake slow, how to work quickly on a big simulation, and how to keep the viewport and renders light.
What a bake costs
A bake's time grows with:
- How many particles are alive. Births a frame times how long they live. Turn on Lifespan so old particles go, unless they should pile up.
- Liquid spacing and smoke cell size. Half the spacing or cell size is eight times the particles or cells, and about twice the substeps: roughly sixteen times the bake. This is the biggest dial there is.
- Particles that touch. Each Other, rigid bodies, and their Rounds cost more than particles that pass through each other.
- Substeps. Twice the substeps, about twice the time.
- The liquid's surface. Detail: twice as fine is about four times the faces.
Smoke only works the cells near smoke, so a plume costs what it fills, not the size of the space around it.
Work quickly, then bake the final
- Draft for smoke and liquids: an eighth of the cells or particles, in a fraction of the time.
- Bake to Frame (Bake menu) for a look at the start, without baking the whole range.
- A shorter frame range while you work on the start of a shot.
- Auto Bake with Draft, to see each change as you make it.
- Re-bake From when only the end of a shot changed.
- Background bakes, to go on working while the final bakes.
Use the GPU
On Windows and Linux, an NVIDIA card bakes big simulations much faster than the CPU, with the same result. Leave Compute on Auto, and check the status box says it ran on the card. With two cards, a big liquid or smoke can be solved over both. See Compute and More than one GPU.
Keep the viewport light
Nothing in the Display panel needs a new bake, so these are free to change:
- Viewport Share: show a tenth of the particles in the viewport. Renders still show them all.
- Sphere Radius: smaller spheres draw faster.
- Shapes with many faces are slow on many particles; keep a low-poly version for the viewport.
More detail without a bigger bake
Render Multiply shows each particle as several at render time, copies scattered round it and moving with it. They aren't baked, so they cost nothing to bake, but they don't collide or push anything: use them for sparks, dust, snow and spray, not for sand, rigid bodies or liquid.
Memory
A simulation that doesn't fit on the GPU says "The GPU ran out of memory". On Auto it bakes on the CPU instead. Spread it over more cards with Cards, mesh the liquid's surface on another card, or lower the detail.