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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 Input Rollout.

Preview & Render Cache Path – Specifies the cache file name in one of the three volumetric formats that VRayVolumeGrid supports (OpenVDB, Field3D, PhoenixFD). If the file was specified when the VRayVolumeGrid object was created, the filename appears here. For a sequence of frames, the file name can contain format specifiers to describe a sequence of files. Environment variables can be used as well, which is explained in the Using Environment Variables with Cache Paths section below. VRayVolumeGrid supports multiple format specifiers:

<frame0n>, where n is an integer specifying the number of digits, and the optional 0 specifies padding with zeros. For example, if you enter cache_<frame04>.vdb as the file name, this is expanded to cache_0000.vdb for frame 0, cache_0001.vdb for frame 1, and so on. The same logic is used for VRayMesh.

# symbols are replaced with the current frame number. Multiple symbols can be used to specify the number of digits in the file name. For example cache_###.vdb is expanded to cache_001.vdb for frame 1.

The form %xd is a deprecated form that can no longer be entered, but works with older .vrscenes that already use this format. The form is resolved to the current Maya frame. The  x,  when present, specifies the minimum number of symbols for the frame number. For example, if the current frame is 9:

%d resolves to "9"
%3d resolves to "··9"
%03d resolves to "009"

Mode | animmode – Chooses between different options for animation control:

Linear – This is the default mode. The cache sequence is played with a constant speed and can be offset forward or backward on the timeline, as well as sped up or slowed down.
Cache Index – The Direct Cache Index specifies which cache file is loaded for the current timeline frame. Can be used to either show a static simulation, or the Direct Cache Index can be animated in case you want varying play speed, including playing the simulation in reverse.
Loop – A specified piece of the simulated sequence is looped. Can be used for flowing and repeated effects such as fireplaces, campfires or torch fires, water in fountains, waterfalls or boiling liquid. In this mode, the Cache Origin parameter specifies the beginning of the looped sequence, the Length parameter specifies the length of the loop, and Loop Overlap specifies the number of overlapped frames that ensure smooth transition between the end and the start of the loop. Note that you need to have simulated at least Cache Origin + Length + Loop Overlap cached frames for this mode to work correctly. 

Direct Cache Index | t2f – Used in Cache Index mode and specifies the cache file index for the current timeline frame. This can be animated in order to achieve more interesting time-bend effects.

Timeline Origin | playat – An offset specifying which timeline frame the starting cache is placed on.

Cache Origin | inpoffset – An offset specifying which cache file from the sequence is placed on the timeline at frame Timeline Origin.

Grid Blend | frmblend  – Used when the Play Speed parameter is not exactly 1.0, or the Direct Cache Index for the current timeline frame is fractional, or you have specified a Loop Overlap in Loop mode. In these cases, a single timeline frame must be constructed from two cache files by blending between them. Each time the timeline is scrolled to a new frame, the caches for this frame are blended again. You can choose between three different methods for blending between cache files:

Interpolation – Simple linear interpolation suitable for slow simulations. This is the fastest method but it does not capture movement well and may produce flickering.

Velocity – Velocity-based interpolation. Produces better results, but is also slower. Captures well the movement of the fronts of the plumes, but does not work well for smoke moving backwards, and also may produce flickering. Requires a Velocity channel.

Precise Tracing - Improved Velocity based interpolation for Fire and Smoke simulations. Captures plume movement very well and can handle very low Play Speeds. Requires a Velocity channel, as well as an Advection Origin channel.

Frame Blending is better suited for simulations without much variety in velocity.

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Different applications use different channels and might have different names for them. When loading f3d/vdb files, Phoenix tries to automatically make the conversion to the supported channels. If a channel is not mapped by default, a channel can be manually set from the dropdown menu. It can be accessed from the Cache Path menu when a 3rd party cache is loaded (e.g. .f3d or .vdb files).

All mappings are kept in a single string parameter, accessible by the name "usrchmap". An example mapping string is:

2,density;10,fuel;1,temperature;4,vel.x;5,vel.y;6 ,vel.z;

The string is composed of pairs of a Phoenix channel index and a string channel name. The following channels with their respective indices are supported:

Smoke - 2
Temperature - 1
Fuel - 10
Velocity.x - 4
Velocity.y - 5
Velocity.z - 6
Red - 7
Green - 8
Blue - 9
Wavelet Energy - 14
Wavelet.u - 19
Wavelet.v - 20
Wavelet.w - 21