Global Volumetric Effects
The global volumetric effects use a three-dimensional "voxel grid", a camera aligned frustum divided into several depth slices parallel to the camera plane along the camera direction. These depth slices are themselves subdivided into a number of frustum shaped voxels along the width and height of the slice (the amount of voxels is controlled by the "Pixel Density").
Settings which are denoted with a * have the most impact on the global volumetrics appearance (other settings can be left at their defaults).
| Setting | Description |
|---|---|
| Accumulation Frames | Number of frames samples are accumulated over temporally. Higher values reduce noise, but increase the amount of time that lighting updates take. |
| # Depth Slices | Number of layers in the voxel grid to be allocated, higher values use more memory and reduce performance but allow for more depth based precision in the volume. |
| Pixel Density | The number of screen pixels each voxel is in width and height. Higher values quickly consume more memory and reduce performance but allow for higher fidelity volumetrics. A value of 4 can give high quality results at the cost of 4x more memory usage than the default value of 8 (beyond that the memory usage goes up quite fast, also depending on the number of depth slices). |
| Max Inscattering Distance | The maximum depth in world units (centimeters) the voxel grid is allocated to. If this is set to 10,000 with 10 depth slices, each slice will span 1,000 units(assuming a slice distribution exponent of 1). Ideally this should be kept as low as possible without causing artifacts in the scene to make the most of the fixed number of depth slices. |
| Atmosphere Height | The height in world units (centimeters) which the volumetric medium ends at. This is useful for providing realistic atmospheres when dealing with infinite light sources, such as distant or dome lights. |
| Transmittance Color | These settings combined define the overall attenuation coefficient for the volume. Assuming a perfectly white light, the transmittance color is the color it will be tinted to after traveling a number of units through the volume as specified by the transmittance distance. |
| Transmittance Distance | The Transmittance Distance controls how far light can travel through fog. Lower values yield thicker fog. |
| Single Scattering Albedo | Base color of the fog under uniform white light. This is the ratio of scattered light to attenuated light for an interaction with the volume. Values closer to 1 indicate a highly scattering medium such as water vapor, while values closer to 0 indicate a highly absorbing medium, such as smoke. |
| Anisotropy Factor | Degree of asymmetry in light scattering. This is the anisotropy of the volumetric phase function, ranging from -1 to 1. -1 is fully backscattering, 0 is fully isotropic, and 1 is fully forward scattering. |
| Slice Distribution Exponent | Controls the number (and relative thickness) of the depth slices |
| Inscatter Blur Sigma | Sigma parameter for the Gaussian filter used to spatially blur the voxel grid. 1 means no blur, whereas higher values blur further. |
| Inscatter Dithering Scale | The intensity of a noise dithering pattern to be applied on top of the volumetric effect. This is typically used to reduce banding from quantization on smooth gradients. |
| Spatial Sample Jittering Scale | A scale parameter for how far light samples within a voxel are spatially jittered (randomized). A value of 0 indicates light samples should only be taken from the center of each voxel, whereas a value of 1 indicates the entire voxel's volume should be randomly sampled from. Should usually be 1. |
| Temporal Reprojection Jittering Scale | A scale parameter for how far to offset a temporally reprojected sample, once again based on a voxel's size. A value of 0 indicates temporal samples should be taken exactly where they are calculated, whereas a value of 1 allows the sample to be offset within a voxel sized area. This acts somewhat like a temporal blur and helps reduce noise under motion. |
| Apply Density Noise | Enables a basic coherent noise texture to modulate the scattering coefficient within the volume, acting somewhat like a density modulation. Note this will not have an impact on the actual overall attenuation as it always assumes the volume is homogeneous as an optimization. Enabling this option will somewhat reduce performance. |
| Density Noise World Scale | A scale parameter to adjust the size of the density noise. Larger values create a more dense noise pattern, whereas smaller values produce a more sparse noise pattern. |
| Density Noise Animation Speed X/Y/Z | A vector to indicate the speed the noise pattern should shift under animation. Note animation needs to be active to display the noise pattern in motion. |
| Density Noise Scale Min/Max | A range to map the noise values of each octave of the coherent noise to. Typically these should be 0 and 1 respectively, but to make sparse points in the noise less sparse a higher min can be used, or a lower max for dense points to be less dense. |
| Density Noise Octave Count | The number of octaves to use in the coherent noise generation. Higher octave counts reduce performance but give more detailed noise patterns. |
| Use 32-bit Precision | Allocate the voxel grid with 32-bit per channel color instead of 16-bit per channel color. This doubles memory usage and reduces performance, generally not too useful unless specifically needed. |