This page provides information on the Volumetric Grid's Smoke tab.
Overview
This tab controls the Volumetric Grid's smoke color and smoke opacity. In general, the diffuse color may be uniform (simple color), a mixture of colors dragged by the simulation (RGB), a function of any physical channel, or sampled from a texture.
UI Path: ||Select VRayVolumeGrid|| > Properties Panel > VRayVolumeGrid node > Smoke tab
Parameters
Smoke Color
Based on – Specifies the source channel used to determine the smoke color. By default, it is a uniform simple color.
Disabled – Disables the diffuse color.
Temperature – Uses the temperature channel.
Smoke – Uses the smoke channel.
Velocity – Uses the velocity channel.
Texture – Uses an external texture map.
Simple color – Uses the color in the Constant color swatch.
RGB – Uses a plain color.
Fuel – Uses the fuel channel.
Modulate – When enabled and Based on is not set to Texture, the color is multiplied by the texture in the dif input.
Constant color – Specifies the color to use if Based on is set to Simple color.
Light cache – Enables light caching for each voxel of the grid. This speeds up 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 the light cache will speed up rendering. This feature might produce artifacts when the smoke is very dense or when objects are casting shadows through the smoke.
Light cache speedup – This value affects the amount of light sampling. Lower values cause less sampling, which speeds up the rendering but decreases the smoke's quality and increases noise. This option is available only when Light cache is enabled.
Scattering – Controls how the light rays are scattered inside the volume.
Ray-Traced (GI only) – If Global Illumination is enabled in the VRayRenderer, this mode enables the scattering of light rays. Otherwise it is the same as Disabled.
Disabled – The scattering of light through the smoke is disabled. The Master multiplier can be used to correct the brightness of the diffuse color in this mode.
Approximate – Without actually altering the rays, an analytic formula is used to calculate the contribution of the scattering to the illumination. Brighter smoke transfers light further than dark smoke. This effect can be controlled from the Constant color box. This option is not supported when Mode is set to Volumetric Geometry.
Approximate+Shadows – Same as Analytic, but geometry is also affected via the shadows. This option is not supported when the Render mode is set to Volumetric Geometry in the Rendering tab.
Scatter depth – Limits the global illumination scattering depth. This can be used to improve performance.
Master multiplier – A general multiplier for the diffuse color. This value is ignored when Scattering is set to Ray-Traced (GI only).
Own light scatter mult – Multiplies the distance that light from emissive lights travels through the volumetric. This value doesn't alter the visual density of the smoke to the camera, and only applies to the illumination. This value affects the lighting only when Scattering is set to Analytic or Analytic+Shadows.
External scatter mult – Multiplies the distance that light from all external light sources travels through the volumetric. This value doesn't alter the visual density of the smoke to the camera, and only applies to the illumination. This value affects the lighting only when Scattering is set to Analytic or Analytic+Shadows.
Shadow Strength – Multiplies the opacity of the shadow that the volumetric casts on other objects.
Color diagram – If Based on is set to a channel of the VRayVolumeGrid, this parameter controls how the smoke color appears based on the channel's value. The selected channel's data range is denoted by a blue-green line.
Smoke Opacity
Based on – The channel that determines the smoke density. The default option is simple smoke, which produces the smoke channel without curve transformation.
Simple smoke – Uses the smoke channel with a predefined analytical formula.
Temperature – Uses the temperature channel.
Smoke – Uses the smoke channel.
Velocity – Uses the magnitude of the velocity channel.
Texture – Uses an external texture map.
Fuel – Uses the fuel channel.
Modulate – When enabled and Based on is not set to Texture, the Based on channel is multiplied by the texture in the tr input.
Simple smoke factor – When the Based on parameter is set to Simple smoke, this value is used as an opacity multiplier.
Scale opacity by scene units – When enabled, the opacity per unit length will remain constant when changing the Grid resolution. Therefore, the larger the unit scale it, the denser the smoke will appear in renders and vice versa. Note: When disabled, Phoenix caches simulated at higher grid resolution will appear more opaque than the same simulation at a lower resolution.
Opacity Diagram – This diagram specifies the transparency/opacity at given point as a function of the channel selected in the Based on parameter. The selected channel's data range is denoted by a blue-green line.
Diagram and Gradient controls
The following controls can be used in the color gradients and diagrams:
Double click – Creates a new point or changes an existing one.
Left button drag – Moves the selected point(s).
Left button drag over the left or bottom rulers (diagrams only) – Scale the diagram in the corresponding direction.
Middle button drag over the background – Drags the visible area. If the Ctrl key is pressed, the background can be dragged instead, thus transforming the diagram.
Mouse wheel – Zoom in/out. If the Ctrl key is pressed, the zoom will occur on the background instead, thus transform the diagram.
Right click – Brings out a drop-down menu where points can be added, edited, or deleted, fit the entire diagram or gradient into the view, clear the diagram, and load and save the diagram it to a file.