Particle disk caching

Specify where the cache files are stored

Maya has a workspace directory for particles. By default, this is given the name particles. You can specify your workspace particles directory using the Project Editor, the same as for all the other workspace directories.

If you are using an old workspace from a previous version of Maya, Maya creates the particles directory for you the first time you create a particle disk cache.

The disk cache files are stored in subdirectories of the particles directory. You can specify what subdirectory name you want to use by entering the name in the Cache Directory box of the Particle Render Cache Options window (see Setting particle disk cache options). Before each new caching operation, Maya automatically deletes any cache files existing in the specified subdirectory.

Determine the frame range

If Maya can’t find a cache file for the given frame, but finds cache files both for frames greater and lesser than the current frame it is evaluating, it interpolates between them. If the frame difference is large, you see the results of interpolation rather than the results of solving frame by frame.

In simple cases, to evaluate a given frame, Maya usually needs the particle cache files only for that frame. However, Maya may need to access the state of particles at some other frame in order to resolve expressions, rigid body motion, motion blur, etc. If you are in doubt, we recommend caching out all frames. For example, if you want to render starting at frame 100, cache all frames up to 100 as well.

Create a particle disk cache

After you have created a particle disk cache, Maya uses the cached particle data, no matter what changes you make to your scene, until you explicitly tell it not to.

For example, if you cache the scene, then apply a gravity field to a particle object, you will not see any effect from that field because Maya is using the cached particle motion. To see the effect, you must turn off Use Particle Disk Cache (see Editing particle disk cache settings).

However, if you make a change that does not alter per-particle attributes, such as changing the render type from blobby to streak, you will see the change without turning off Use Particle Disk Cache.

To create a particle disk cache

1. Select Solvers > Create Particle Disk Cache.

   Maya plays through the scene once using the current time slider playback range and writes out cache files. Maya does not re-draw the screen during this playback. If you want to cache a different range, you can either change the current range of your time slider or turn on Use render settings range (see Use Render Settings Range).

   Maya must play the scene through once to create the cache. If you don’t want to wait through the playback, you can interrupt it by pressing the Esc key, but the cache won’t be created.

2. After creating the cache, save your scene so any settings you made to the Particle Render Cache Option window get saved with the scene. Otherwise Maya might not know to look for your cache or might not be able to find it.

   When you create the cache in the above manner, Maya creates a cache for all particles in the scene. If you want to cache some particles objects and not others, see Caching a single particle object.

   Note

   Be sure to save your scene after creating the cache. Otherwise, Maya won’t know about the cache when batch rendering.

Setting particle disk cache options

You can set the following particle disk cache options before creating the cache. These options affect all subsequent caching operations.

To set the particle disk cache options:

1. Select Solvers > Create Particle Disk Cache > .
2. Set the following options:
   • Solvers > Create Particle Disk Cache

Editing particle disk cache settings

To edit particle disk cache settings

1. Select Solvers > Edit Oversampling or Cache Settings.

   The Attribute Editor for the dynGlobals node is displayed.

2. In the Particle Disk Cache section, set the settings. See Particle Disk Cache.
   Note

   Be sure to save your scene after editing any of these values. Otherwise, Maya won’t know about them when batch rendering.

Play back different caches

You can use particle disk caching to create different caches for the same scene. This lets you create and quickly play back variations on a scene.

To create and play back different caches

1. Create your scene and name it.
2. Select Solvers > Create Particle Disk Cache > .
3. Enter a name for the Cache Directory or leave the default name, which is the scene name.
4. Click Create to create the cache.
5. Make any changes to your particles.
6. Select Solvers > Create Particle Disk Cache > .
7. Enter a new name for the Cache Directory and click Create.
8. Continue this process to create as many caches as you want.
9. To choose a cache for playback, select Solvers > Edit Oversampling or Cache Settings, and enter the cache name in the Cache Directory box.
10. Press the play button to see the scene play back from the specified cache.

Re-create the cache

Once you have created the cache, Maya uses that cache until you tell it not to. It ignores any changes in emission, forces, etc. on that particle object.

If you change something in the scene that alters per-particle attributes, you must re-create your cache in order to get correct renders. Maya writes out the disk cache only when you select Create Particle Disk Cache. That menu item does not turn on a “caching state.” This is an important difference between memory caching and disk caching. Maya does not automatically update or re-create your disk cache.

To re-create your cache

1. Select Solvers > Create Particle Disk Cache.

You don’t need to re-create the cache if you make a change that does not alter per-particle attributes. For example, you could change a particle shape’s render type from blobby to cloud, save the file, and re-render. Or you could change keyframed colorRed/colorBlue/colorGreen attributes. In both these examples, you would not need to re-create the cache because the attributes involved are not per-particle.

Be careful, however, because attributes such as colorRed can indirectly affect per-particle attributes. In the previous examples, if you had a per-particle expression on some particle object that made use of the render type or colorRed as an input, the results of that expression would be affected, so you would need to re-create the cache.

Particle disk cache files

Maya saves cache files for each particle shape for each frame. If oversampling is turned on, it saves multiple disk caches at different times within a frame depending on the oversampling rate.These binary files have the extension .pdc, which stands for particle data cache. Maya uses the dynExport command to write these files.

You can’t read .pdc files. If you want to output particle data files you can read, see the online documentation in the dynExport command for information on outputting .pda and .pdb files, and also the ExploreMe/particlesreadpdb directory on the Maya DVD. See Appendix Use the PDC File Format for information on writing your own reader.

Deleting cache files

There is no way to delete cache files or directories from within Maya. Delete them using your operating system.

Caching tips

bakeResults -t "1:100" -simulation true rigidBody1;