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This page provides information on the Smoke color rollout the Rendering Volumetric Options dialog.
Overview
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This roll-out controls the Diffuse color of the Volumetric Shader. The Smoke Color can be a uniform color, a mixture of colors dragged by the simulation (RGB), a function of any physical channel, or sampled from a texture. It is also affected by lights and shadows cast by objects in the scene. |
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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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Parameters
Based on | darg – 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 roll-out before the simulation is run.
- Disabled - the smoke color will not be rendered.
- Temperature - the smoke color will be based on the values of the Temperature cache channel and can be remapped using the color gradient.
- Smoke - the smoke color will be based on the values of the Smoke cache channel and can be remapped using the color gradient.
- Speed - the smoke color will be based on the values of the Speed cache channel and can be remapped using the color gradient. See the Smoke Color by Speed example below.
- Texture - the smoke color will be based on the values of a texture map plugged into the Texture slot.
- Constant Color - the smoke color will be the same for the entire volume and will be taken from the Constant Color box.
- RGB - the smoke will be based on the values of the RGB channel.
- Fuel - the smoke will be based on the values of the Fuel channel and can be remapped using the color gradient.
? – Opens the help documents.
Texture | dtxt – If Based on is set to Texture, this slot specifies which texture to use.
Modulate | mod_d – When Based on is not set to Texture, the color is multiplied by the texture in the Texture slot.
Reset to Defaults – Resets the settings to their default values.
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Constant color | simple_color – If Based on is set to Constant color , this color is used. |
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Scattering | noscatter – Controls how the light rays are scattered inside the volume. |
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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 Master Multiplier does not affect the rendering in this mode. |
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Disabled – Disables scattering. The Master Multiplier value can be used to correct the brightness because without light scattering the volume would generally render darker. |
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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. |
Volume Light Cache | lightcache – 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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Light Cache Speedup | subred – [V-Ray specific] [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.
Master Multiplier | difmul – A general multiplier for the diffuse color. It is ignored when the Scattering mode is set to Ray-traced (GI only).
Own Light Scatter Mult | transfown – [Valid only when Scattering is set to Approximate or Approximate+Shadows] This multiplier determines how far the light travels through the volumetric, based on the distance from the emissive light itself.
External Light Scatter Mult | transfext – [Valid only when Scattering is set to Approximate or Approximate+Shadows] This multiplier determines how far the light from all external light sources travels through the volumetric. Both Scatter Boost parameters don't alter the visual density of the smoke to the camera, and only apply to the illumination.
Shadow Strength | shad_strength – A multiplier for the opacity of the shadow that the volumetric casts on other objects.
Color gradient | dcolorx_t, dcolory_t, dcolorx_s, dcolory_s, dcolorx_v, dcolory_v, dcolorx_f, dcolory_f – When the Based on option is set to a grid channel, this color gradient remaps grid simulation data to render smoke color. The sim data channel is laid out horizontally along the X axis in the color gradient.
The channel data range is highlighted in the curve with a light-blue range. You can find out more about Phoenix Grid Channel Ranges here.
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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. |
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Example: Smoke Color Based on Speed
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