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The diffuse color needs external light to become visible if GI is enabled in the V-Ray Render Settings in Maya.

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UI Path: ||Select PhoenixFDSim|| > Attribute Editor > Rendering rollout > Smoke Color rollout

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Phase Function | phase_function – Controls the direction in which the light will scatter inside the volume. Negative values correspond to backward scattering, which mimics a volume made up of solid particles and will produce denser and more detailed looks. Negative values are more suitable for smoke or dust effects. Positive values correspond to forward scattering, which mimics a volume made up of water droplets where light will scatter more. Positive values are suitable for highly scattering volumes such as clouds. The default value of 0 will scatter the light in all directions and create an even and diffuse look. For more information, see the Phase Function example below.

Note that values very close to 1.0 or -1.0 will produce very directional scattering that will be invisible from most angles, so such values are not recommended. When rendering with a Phase Function different than 0 and Volume Light Cache is enabled the rendered result will be brighter. The Phase Function is ignored when the scattering is set to Approximate or Approximate+Shadows.

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Volume Light Cache | difLightCache – Enables light caching for each voxel of the grid, which speeds up bucket rendering considerably when the voxel size of the grid is significantly larger than the rendering pixel. If the grid resolution is large enough compared to the rendering resolution, disabling this option will speed up rendering.

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  • This option refers to the internal Phoenix
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  • Light Cache, which is not related to the V-Ray Light Cache.
  • This option is ignored when using V-Ray GPU or Corona. It works with V-Ray CPU.
  • When using V-Ray Progressive Rendering,
this
  • the Volume Light Cache option might slow down rendering startup or the overall render speed. 
  • This
feature
  • option might produce artifacts when the smoke is very dense.
  • This
feature
  • option might produce artifacts when objects cast shadows through the smoke.
  • Rendering multiple copies or instances of the
simulator
  • Simulator node with this option turned on might lead to slow-downs.
  • This option will consume additional memory, so beware of high RAM usage when rendering very large cache files or a large number of copied or instanced volumes.
  • When rendering in Volumetric Geometry mode, for any of these Render Elements: [ Shadow ], [ Raw Shadow ], [ Global Illumination ], [ Raw Global Illumination ] , the Volume Light Cache will require additional memory to produce the correct result.
Please be aware that these Render Elements (and most other V-Ray Render Elements except for [ Atmosphere ] and [ Self-Illumination ] ) do not work in Volumetric mode.This option is ignored when using V-Ray GPU. It is a CPU-only feature that helps speed up Bucket rendering
  • Some V-Ray render elements might not work when Volume Light Cache is enabled. Please consult this table.

Light Cache Speedup | difLightCacheSR – [Valid only when Volume Light Cache is enabled] The higher this option is set, the faster the rendering will be, but the lower the quality of the Volume Light Cache. You can increase this parameter and gain render speed as long as you don't start getting dark cubic grid artifacts on the smoke.

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You can use the following controls in the color gradient:

Double click – Creates a new point or changes an existing one.
Left button drag over a point – Moves the point. If several points were selected beforehand, they will move the same amount.
Left button drag over several points – Selects several points.
Middle button drag over the background – Drags the visible area.
Mouse wheel – Zooms in/out.
Right-click – Displays a drop-down menu where you can add a point, edit or delete a selected point, and fit the entire gradient into the view. If multiple points are selected, they can be edited simultaneously.


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Example: Phase Function with front lighting

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Phase Function = -0.5

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Phase Function = 0

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Phase Function = 0.5

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Phase Function = -0.5 (Backward Scattering) 

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Phase Function = 0 (Isotropic Scattering)

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Phase Function = 0.5 (Forward Scattering)


The orange arrow represents a ray of light going through the volume and the possible scattering directions for the ray.

 

Example: Phase Function with back lighting

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Phase Function = -0.5

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Phase Function = 0

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Phase Function = -0.5 (Backward Scattering) 

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Phase Function = 0 (Isotropic Scattering)

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Phase Function = 0.5 (Forward Scattering)


The orange arrow represents a ray of light going through the volume and the possible scattering directions for the ray.


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Example: Smoke Color Based on Speed

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The Smoke Color can be based on any channel present in the cache files. The Speed channel can be used to drive the color of the smoke. It is automatically generated by Phoenix based on the Velocity Grid Channel. In this example, the slowly moving smoke is blue while the fast moving smoke is red to yellow.

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<iframe width="720" height="405" src="https://www.youtube.com/embed/TzD4Vh_DtzM?version=3&loop=1&playlist=TzD4Vh_DtzM" frameborder="0" allowfullscreen></iframe>


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