Bake, upres and checkpoints
The Simulation Output node of a Blaze graph has a Mode that decides what Run and Bake do.
| Mode | What it does |
|---|---|
| Live | The interactive preview. Nothing is cached unless Bake on Preview is on. Keep as Bake promotes those cached frames to a bake. |
| Bake | Writes VDBs at the simulation’s resolution, with velocity and rest grids. |
| Bake + Upres | Bakes, then adds sub-grid detail at 2x, 3x or 4x. |
| Upres from Cache | Re-runs only the upres pass over an existing bake. |
Bake on Preview caches a live run’s frames at the live settings: smoke, heat, fuel and flame, with no velocity or rest grids.
Upres uses wavelet turbulence (Kim, Thürey, James and Gross, 2008). Smoke, fire and heat are re-advected at 2x, 3x or 4x the resolution through the simulation’s velocity plus divergence-free wavelet noise. The noise follows the gas and is scaled by the simulation’s own turbulent energy. Their coarse shape is kept equal to the simulation’s.
| Setting | What it does |
|---|---|
| Upres | 2x, 3x or 4x the simulation’s resolution. |
| Upres Turbulence | Amplitude of the sub-grid turbulence, relative to the estimate from the simulation’s own turbulent energy. 0 keeps only the smooth upsampled gas. |
- Velocity, burn and the rest fields stay at the simulation’s resolution in the same VDB.
- Upres from Cache lets you change the upres settings without re-simulating.
- Upres runs in bakes only, never in the live preview.
- 4x costs several times the simulation itself, and 64 times the voxels on disk.
Checkpoints
Section titled “Checkpoints”A bake writes a checkpoint of the whole solver state every Checkpoint Every frames. The default is 10, and 0 turns it off.
| Button | What it does |
|---|---|
| Resume Bake | Continues an interrupted bake from its last checkpoint. |
| Re-bake from Here | Re-simulates from the checkpoint at or before the current frame. Use it after changing something late in the shot. |
- Only checkpoints of the same scene and settings are used.
- An upres pass restarts after a resume.
- A checkpoint of a full 128³ dense grid is about 120 MB. They live in the cache folder and count toward the disk budget. See Cache and budgets.
Baked frames are sparse OpenVDB files, one leaf per 8³ brick of gas, with Blender’s grid names: density, temperature, flame, fuel and velocity, plus burn and the rest fields.
temperatureis absolute kelvin, so Blender’s own Principled Volume reads it too.- Half-Float VDB on the Simulation Output node stores 16-bit floats: files about 0.55 times the size.
- Two rest-position grids let the render noise move with the smoke. Each restarts every Rest Reset frames (24 by default).
Caches baked by an older build stored temperature in solver units and render too cold. Re-bake them.
Output
Section titled “Output”Export a bake as an OpenVDB sequence, or as a game-engine flipbook. See Baking and exporting and Spritesheets.