Preview a Bifröst simulation with a scratch cache

The scratch cache is a temporary cache to speed up playback and scrubbing. It is intended for quick previews at low-to-medium resolutions, unlike user caches which are intended for the final, high-resolution result.

The scratch cache stores the simulated frames in memory, and offloads them to temporary files on disk. It is automatically flushed and regenerated when you change the simulation and return to the first frame. It also gets deleted automatically when you close the scene.

1. Make sure that Playback speed is set to Play every frame in your Settings > Time Slider preferences.
2. Select Bifrost > Bifrost Options, and make sure that the options are set as you want them. In particular, make sure that Maximum RAM Usage (GB) is less than your system memory minus some overhead. See Bifrost Options.
3. Make sure that Scratch Cache is enabled on the main container node (e.g. bifrostLiquid or bifrostAero).
   Note: You can use Enable Scratch Caching in the Bifrost Options dialog box to toggle Scratch Cache on or off for all container nodes in the scene.
4. Go to the start frame of the simulation.

   By default, the start frame is 1 but you can set a different value in the container's attributes.

5. Do any one of the following:
   • Step forward.
   • Play back. You can stop playback at any time.
   • Go to any later frame on the timeline, if Run up to current time is set in your Dynamics preferences.
   If Enable Background Processing is on in the Bifrost Options dialog box:

   • All frames in the specified range are sent to the Bifröst Computation Server.
   • Frames that are in the queue for processing are displayed in yellow on the timeline when the main container or shape object is selected.
   • Frames that have been computed and cached are displayed in bright green on the timeline when the main container or shape object is selected. You can quickly replay or scrub through these frames.
   • When objects from multiple simulations are selected, multiple lines are displayed in the timeline.
   • You can stop the processing of frames in the queue by clicking Stop at the bottom right of the Maya window, or by choosing Bifrost > Stop Background Processing. Note that processing will stop only after the current frame is finished.

   If Enable Background Processing is off, then you must wait for all frames to be processed before you can interact in Maya.

6. If you change the simulation settings or modify the input objects, the cached frames get marked as "dirty" and displayed in dark green on the timeline when the main container or shape object is selected.
   • You can still play or scrub through any frame except the first frame of the simulation to view the cached results, but they will not reflect the changes you made.
   • When you return to the first frame of the simulation, the cache is flushed automatically. The updated results of the simulation will be recached as you play back or step forward again.
   • If desired, you can flush the frames manually by selecting the main container or shape object and choosing Bifrost > Flush Scratch Cache. You can then re-cache the frames by repeating steps 4 and 5.

Tip: You can activate Bifrost > Display Bifrost HUD to show the number of Bifrost particles and voxels as a heads-up display, as well as the number of time steps per frame. The values reflect the actual numbers of elements in the scene and in the selected objects, and not the numbers of elements being drawn in the viewport (which can be adjusted using Max Particle Display Count in the bifrostShape attributes's attributes).