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In the Output rollout, you can choose which Particle Channels and Grid Channels to export to the cache files, based on your needs.

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Phoenix Liquid simulators can simulate several particle system types: Liquid, Foam, Splash, Mist and Wetmap particles. Each of these particle systems contains Particle Channels for each particle, such as Position, Size, Age, ID, Velocity and so forth. The Output rollout lets you manage which of these are exported.

Likewise, there are several Grid Channel types, such as Liquid, Velocity, RGB and so on. For Liquid simulations, the Grid Channel data is built from the simulated particles, and then exported to the cache files in the form of a voxel grid, where the Grid channels are contained in each of the voxels.

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Exporting the Grid Liquid Channel willautomatically convert Liquid particles to a grid during export, which is why they can be rendered as a mesh and shaded using standard materials. In addition, the Liquid mesh can also be previewed in the viewport.

Note that only Liquid particles can be automatically converted to a grid. The other particle systems (e.g. Foam, Splash, Mist etc.) are exported only as particles, and must be shaded using the Particle Shader.

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UI Path: ||Select Liquid Simulator object|| > Modify panel > Output rollout

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Expand – Opens a floating dialog that contains the selected rollout and automatically folds the command panel rollout.

? – Opens up the help documents for the Liquid Output.

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	CachePath
	CachePath

Simulation Cache Save Path | simoutput – This is the directory and the name template for the output cache files. It uses the $(scene_path) macro by default, and there are also other available macros as listed below. To set up rendering and simulation cache paths manually, see How to change the default Phoenix paths on the Tips and Tricks page.

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title	Click Here to expand additional $(VARIABLE) information

$(scene_path) – $(data_dir)\$(scene)_Phoenix_frames\$(nodename)_####.aur
$(scene_dir) – $(data_dir)\$(scene)_Phoenix2_frames\ND$(handle)_$(nodename)_####.aur
$(implicit) – Same as $(scene_dir)
$(dir) – The scene directory.
$(data_dir) – The default directory where cache files are written. By default this is $(dir), meaning that the cache files are written next to the scene file, but it can be overridden with a custom directory from the Phoenix Global Preferences.
$(scene) – The scene file name.
$(handle) – A unique number of the node.
$(nodename) – The name of the node.
$env(<variable_name>) – An environment variable. See Using Environment Variables below.

#### is the frame number formatted with at least as many digits as the hash signs. If the frame digits are less than the hashes, the number is padded with zeroes to the left. For example:

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		Result
Frame Number	#	##	####
1	1	01	0001
10	10	10	0010
1000	1000	1000	1000

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Backup Interval | backup – The frame interval between backups of the full simulation state. A stopped simulation can be restarted from such frames (see the Restore option in the Simulation rollout). To make restoring possible from every frame, set this value to 1. A value of 0 means no backup frames will be exported.

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	outputParticles

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Compress Particles | prtcompress – Enables compression of the simulated particle systems when they are written to AUR cache files. VDB cache files exported from Phoenix do not support particle compression. Simulations with very high particle counts, such as 50 million or more, will produce large caches, so particle compression will help reduce the cache sizes significantly. If you are writing or reading the cache files over the network or to a disk drive, this could significantly speed up simulation and rendering. However, if you are writing the simulation caches to an SSD drive or other fast storage, and you can afford to have large cache files, then disabling the compression could actually speed up the simulation.

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Example: Particle compression artifacts

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For particle systems such as Liquid or Foam, the artifacts would look like ordered lines of particles, as in the following comparison (click to zoom in):

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Image Modified

Storage quality = 19

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Storage quality = 14
(artifacts in the lower left corner)

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Storage quality = 8

Note that writing more channels to the cache files takes more time and will add up to the simulation time, so if you know in advance that you will not be needing a certain channel for rendering, then it would help the simulation times if you turn it off.

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Particle ID – The ID channel will be exported. This channel is used during rendering to identify each particle. Use it when render time size variation is needed, if you would use the Particle Shader's Count Multiplier, or when frame blending will be involved (animated frame index or non-integer play speed).

Particle Age – The particle age channel will be exported. This channel can be used for animation effect based on the particle age, which can be needed by the Phoenix Particle Texture, Phoenix Source, Particle Shader, or Particle Tuner.

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The Age channel is affected by the Time Scale option under the Dynamics rollout which acts a multiplier for the Age.

Particle RGB – The particle RGB channel will be exported. You can use this for simulations where you are mixing different particle colors or you shade the particles by the particle RGB channel through a Particle Texture. Also, enable this if you want to be able to preview the RGB channel as a particle color in the viewport.

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Grid Liquid | keep_t – Export the liquid amount. This is needed so that you can render the Liquid as a mesh and also preview it as a mesh in the viewport.

Grid RGB | keep_rgb – Export the RGB color. You can use this for simulations where you are mixing different liquid colors or materials through a Phoenix FD Grid Texture.

Grid Velocity | keep _vxyz – Export the velocity. This is needed for motion blur of the liquid mesh.

Grid Viscosity | keep_visc - Export the Viscosity channel. Required for variable Viscosity simulations You may also choose to enable this if, for instance, your setup requires that you use the Viscosity channel as a mask through a Phoenix FD Grid Texture.

Grid Texture UVW | keep_texuvw – Export the Texture UVW channel. Enable this to generate texture mapping coordinates that follow the movement of the fluid.

Special | zmr – Export internal or special channels into the Special channel (alias to the Smoke channel) so they can be visualized using one of the volumetric shaders of the FireSmoke Simulator (with Mode set to Volumetric, Volumetric Geometry, or Volumetric Heat Haze). Such channels can also be read by the Grid Texture and used for rendering.

Solid Voxels – Exports the solid voxels as smoke. Voxels covered by many obstacles contain more smoke.
Divergence Symm – Exports the negative divergence of each voxel.
Divergence Smooth  – Exports the blurred negative divergence of each voxel.
Vorticity – Exports the length of the curl of each voxel. Can be used for whitewater shading.
Vorticity Smooth  – Exports the blurred length of the curl of each voxel. Can be used for whitewater shading.
Velocity Gradient – Exports the length of the gradient of the velocity field.
Injector  – Exports the pressure term created by sources in Inject mode or formed during the simulation.
Liquid Surface – Exports the surface created by the simulation.
Solid Geom Type – Exports the internal geometry type in each voxel.
Hydrostatic Pressure – Exports the pressure of the liquid at each voxel due to the effect of gravity.
Voxelization Issues – Exports voxels where the solver would produce wrong results during simulation. Such voxels are near overlapping triangles, inverted normals, open edges or other geometry issues.

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	environmentVariables

Using Environment Variables with Phoenix Paths

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Note that in order to reference environment variables, the following pattern must be used:

$env(<variable_name>)

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Old Version 25

New Version 26

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Example: Particle compression artifacts

Using Environment Variables with Phoenix Paths