This page provides general information about the Smoke Color sub-section of the Rendering tab of the V-Ray Volumetric Grid.
Overview
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.
The diffuse color needs external light to become visible if GI is enabled in the V-Ray Render Settings in Cinema 4D.
Parameters
Based on – Specifies the source channel 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 present in the cache files and remapped to the internal Volume Grid channels using the 3rd Party Channels Mapping dialog in the Input roll-out.
Disabled - Smoke color is not rendered.
Temperature - Smoke color is based on the values of the Temperature cache channel and can be remapped using the color gradient.
Smoke - Smoke color is based on the values of the Smoke cache channel and can be remapped using the color gradient.
Speed - Smoke color is based on the values of the Speed cache channel and can be remapped using the color gradient. See the Smoke Color by Speed example.
Texture - Smoke color is based on the values of a texture map plugged into the Texture slot.
Constant Color - Smoke color is the same for the entire volume and is taken from the Constant Color box.
RGB - Smoke is based on the values of the RGB channel.
Fuel - Smoke is based on the values of the Fuel channel and can be remapped using the color gradient.
Smoke Color Texture – If Based on is set to Texture, this slot specifies which texture to use.
Modulate by Texture – When Based on is not set to Texture, the color is multiplied by the texture in the Texture slot.
Constant Color – If Based on is set to Constant color, this color is used.
Scattering – Controls how the light rays are scattered inside the volume.
Ray-traced (GI only) – Enables physically accurate scattering of light rays. This mode produces the most realistic results but is 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.
Disabled – Disables scattering. The Master Multiplier value can be used to correct the brightness because, without light scattering, the volume would generally render darker.
Approximate – Uses an approximate formula that 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 in the Rendering tab.
Approximate+Shadows – Same as Approximate, but also affects the strength of shadows over the scene geometry. Approximate+Shadows is not supported by the Volumetric Geometry render mode in the Rendering tab.
Phase Function – Controls the direction in which the light scatters inside the volume. Negative values correspond to backward scattering, which mimics a volume made up of solid particles and produces 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 scatters more. Positive values are suitable for highly scattering volumes such as clouds. The default value of 0 scatters the light in all directions and creates an even and diffuse look. See the Phase Function examples for a visual representation.
Note that values very close to 1.0 or -1.0 produce very directional scattering that is 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 is brighter. The Phase function is ignored when the scattering is set to Approximate or Approximate+Shadows.
Optimize Anisotropic Scattering – When enabled, it can greatly reduce the render times for highly scattering volumes such as clouds. Due to certain assumptions made for the optimizations, the optimized render result might produce different results than the exact brute-force anisotropic scattering. The option is ignored when the scattering is set to Approximate or Approximate+Shadows.
Scatter Depth – Specifies the maximum depth of the GI rays.
Volume Light Cache – 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 speeds up rendering.
- This option refers to the internal Volume Grid Light Cache, which is not related to the V-Ray Light Cache.
- When using V-Ray Progressive Rendering, this option might slow down the rendering startup or the overall render speed.
- This feature might produce artifacts when the smoke is very dense.
- This feature might produce artifacts when objects cast shadows through the smoke.
- Rendering multiple copies or instances of the Volume Grid 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: [ Shadows ], [ Raw Shadows ], [ Global Illumination ], [ Raw Global Illumination ], the Volume Grid 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.
Light Cache Speedup – 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 volumetric 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.
Own Light Scatter Mult – 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 Scatter Mult – 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.
Master Multiplier – A general multiplier for the diffuse color. It is ignored when the Scattering mode is set to Ray-traced (GI only).
Shadow Strength – A multiplier for the opacity of the shadow that the volumetric casts on other objects.
Example: Smoke Color Based on Speed
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 the V-Ray Volume Grid based on the Velocity Grid Channel. In this example, the slowly-moving smoke is blue, while the fast-moving smoke is red to yellow.
Example: Phase Function with Front Lighting
Phase Function = -0.5
Phase Function = 0
Phase Function = 0.5
Phase Function = -0.5 (Backward Scattering)
Phase Function = 0 (Isotropic Scattering)
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 Backlighting
Phase Function = -0.5
Phase Function = 0
Phase Function = 0.5
Phase Function = -0.5 (Backward Scattering)
Phase Function = 0 (Isotropic Scattering)
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.
Smoke Color Gradient
Smoke Color gradient – When the Based on option is set to a grid channel, this color gradient remaps grid simulation data to render smoke color.
This sim data has different ranges, depending on the solver it came from - Phoenix Smoke usually goes from 0-1; Fuel goes from 0-1; Temperature is in Kelvins, so it goes from 300-2000, or a few thousand; Speed is in Voxels/sec, so it depends on the grid size and resolution but usually goes from 0 to several hundred. Data from other solvers often differs a lot from Phoenix ranges. The cоlor gradients in Cinema 4D are using the 0 to 1 range. When the sim data goes outside the 0 to 1 range, the gradient needs to be remapped through the Gradient Min and Gradient Max values in order to match the grid channel range. You can find the exact range of your grid channels in the Frame Info tab.
Gradient Min – Remaps the minimum value used for the Gradient.
Gradient Max – Remaps the maximum value used for the Gradient.
