Page History
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In the volume shader, there are two types of content - diffuse and emissive. For simplicity we call the diffuse content 'Smoke' and the emissive content 'Fire', though the volume shader is flexible enough that you can render a simulation's fire as smoke and a simulation's smoke as fire. Diffuse needs external light in order to become visible, and also casts shadows. Emissive on the other hand is visible even without being lit by lights, ignores their illumination and does not cast shadows on itself. In addition, Phoenix has different tools that help you gain more control over how fire illuminates the smoke and the scene - see the Create Fire Lights section. Both smoke and fire have their own color and alpha (alpha is a synonym for opacity, and transparency is the opposite of opacity). Fire color and alpha, smoke color and smoke alpha can each be mapped to a physical grid channel, coming from the simulation. Color gradients are used to remap a physical channel to render color, and the diagrams (also called ramps or curves) are used to remap a physical channel to render opacity or intensity. Also, each of them can be mapped to a texture, or to a grid channel multiplied by a texture. Textures have infinite resolution and can increase the detail above the resolution of the grid; By default textures are static in space, but using TexUVW they can move together with the fluid. When there are both diffuse and emissive (smoke and fire) in the same voxel, there are 3 ways to determine the resulting color and alpha in that voxel - see the Fire Opacity Mode option. |
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UI Path: ||Select PhoenixFDSim|| > Attribute Editor > Rendering rollout > Smoke Color rollout |
Parameters
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Based on | difSource – Specifies the source channel that will be used to determine the smoke color. By default, a uniform simple color set by the Constant Color option is used. This could also be a texture map, or read from the cache files - in that case the corresponding grid channel must be enabled from the Output rollout before the simulation is run.
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Texture | difTexture – If Based on is set to Texture, this slot specifies which texture to use. For more information on texture mapping in Phoenix, please check the Texture mapping, moving textures with fire/smoke/liquid, and TexUVW page.
Modulate | difModulate – When Based on is not set to Texture, the color is multiplied by the texture in the Texture slot.
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Ray-traced (GI only) – Enables physically accurate scattering of light rays. This mode produces the most realistic results but it's the slowest to render. It requires V-Ray with enabled Global Illumination, otherwise the rendered result would be the same as if the option is Disabled. The Diffuse Multiplier does not affect the rendering in this mode. Use this mode when you want to render bright clouds.
Disabled – Disables scattering. The Diffuse Multiplier value can be used to correct the brightness because without light scattering the volume would generally render darker.
Approximate – Uses an approximate formula which is faster than Ray-Traced scattering and produces good-looking results. Brighter areas of the volume would transfer light farther than dark areas. This option is not supported by the Volumetric Geometry render mode.
Approximate+Shadows – Same as Approximate, but also affects the strength of shadows over the scene geometry. This option is not supported by the Volumetric Geometry render mode.
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