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# Air's Volume Primitive

MayaMan will render using Air's Volume primitive in two circumstances, a 3d-fluidShape that is set to 'volume' mode or a particleShape that is set to 'cloud' rendering

### Fluid Shape

A 3d fluidShape in volume rendering mode will be exported as Volume primitive. The density, temperature, fuel and pressure grids will go into the rib and can be accessed from a shader under then names 'fluid_density', 'fluid_temperature', 'fluid_fuel', "fluid_pressure'.

The 'realLights' attribute of the fluid shape is observed, lights are not sampled when it's off and a simple diffuse term is computed according to the directionalLight parameter when it's on.

The 'selfShadowing' attribute for the volume will be taken from the fluidShape's own selfShadowing flag.

The 'shadowOpacity' attribute of the fluidShape is mapped to the 'shadowdensity' attribute of the volume primitive... only a single constant value is used, mapping of this parameter is not supported.

### Particle Shape

A particleShape that is set to 'cloud' rendering mode will be exported as a Volume primitive. The radius/radiusPP attributes control the width of each point.

The age data is always exported.

The 'Better Illumination' attribute that is added to the particleShape when Maya's 'Add Attributes For Current Render Type' button is pushed can be used to control the Volume primitive's self shadowing.

### Shaders

The best way to build a shading network for use with a volume primitive is to create a maya 'particleCloud' shader just like you would expect except you need to go into the shadingEngine node and move the 'Volume Material' connection to the 'Surface Material' connection as the volume primitive is looking for a surface shader rather than a volume shader... do this by cut-n-pasting the name that appears in the volume shader slot over to the surface shader slot and then 'break connection' on the volume material slot. Using a particleCloud shader will give the apropos illumination with obvious points to connect color and opacity. Note that if you have a rgbPP and/or opacityPP attributes then the particleCloud shader will automatically pick them up.

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