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title: "V-Ray Volume Shader"
canonical: "https://documentation.chaos.com/space/VRAYHOUDINI/113279163/V-Ray%20Volume%20Shader"
format: markdown
---
This page provides information about the V-Ray Volume Shader node. Overview The V-Ray Volume Shader is the 'core' node of V-Ray’s new implementation of volumetric rendering. The V-Ray Volume Shader enables the work with volumetric shading graphs by exposing inputs for density, color, absorption, and anisotropy. The inputs can be mapped by textures to create procedural shading graphs by sampling the voxel information for each VDB primitive in the VDB file. The V-Ray Volume Shader is used for clouds, smoke, and magical effects. Currently, there is no support for rendering fire on its own, i.e. without smoke. The Volume Shader supports both float and vector velocity fields. However, for 'legacy' (non-Solaris) this preview implementation expects a float velocity field in the form of vel.x, vel.y, vel.z. The Volume Shader supports VDB volumes only. Parameters Smoke Density Scale  – Multiplier for the volume thickness. Extinction Falloff  – Specifies the rate at which volume density decreases for higher scatter bounces. Values greater than 0 result in an exponential reduction of the volume density for successive scatter bounces. This way, the light propagation through highly scattering volumes such as clouds can be simulated with a lower number of scatter bounces. Values around 0.25 can be used as a starting point for creating a cloud shader. Extinction Start  – Specifies the scatter bounce where density reduction begins. The value of the parameter gives the last scatter bounce that is unaffected by the falloff. Smoke Color  – Specifies the base scatter color of the volume when illuminated by a light source. Absorption Color  – Specifies the attenuation of light passing through the volume. Fire Mode  – Specifies how emission is calculated from the emission and temperature input sockets. Disabled  – No emission. Artistic  – The emission-tex input socket is used, ideally with a Gradient Ramp VOP in Position mode and input Volume Float Sampler VOP reading, e.g. a Flame field. Blackbody  – A blackbody radiation model is used to compute the fire color and intensity using the temperature_tex input socket. Ideally, the Blackbody model is used with a Volume Float Sampler VOP reading, e.g. a Temperature field. As the default Pyro temperature values are non-physical, the Temperature Scale parameter can be used to modify the volume field values to physical (Kelvin) values. Additionally, the emission_tex input socket can be used to further modulate the result of the blackbody model output. Color  – When using the Artistic mode, specifies the volume emission (self-illumination) color. When using the Blackbody mode, acts as a multiplier. Temperature Scale  – Multiplier for the temperature_tex input socket, used when the Mode is  Blackbody . Its purpose is to provide a handy scale factor option to bring the default Pyro simulation values to a real-world, physical Kelvin range. Scaling  – Specifies how the final illumination is calculated. No Multiplication  – Used when the goal is to render fire without smoke. Mult. by Smoke  – The emission is multiplied against the Smoke. Thus, setting the Density Scale to 0 also produces no illumination. Mult. by Absorption  – The final illumination is affected by both the Smoke Scale and Smoke Color. Anisotropy Anisotropy  – Controls forward or backward scattering (Hen–Greenstein phase function). Accepts values in the interval [-1 1]. Negative values correspond to backward scattering, positive values correspond to forward scattering, and a value of zero - to isotropic (diffuse). Roughness  – Specifies the rate at which the Anisotropy is reduced for higher scatter bounces. Setting the Roughness to a value greater than 0 leads to an exponential reduction of the phase function asymmetry for the successive higher scatter bounces. This simplifies the multiple scattering computation, which can significantly reduce render times. Besides that, the Roughness can potentially be used to bring back the volume shape details, which otherwise will be lost if using a highly anisotropic phase function, while retaining the silver lining effect. A roughness amount of around 1 can be used as a starting point for creating a cloud shader. By default, the anisotropy reduction is engaged after the first scatter bounce.  Roughness Start  – Specifies the bounce after which roughness effects begin. Options Scatter Limit  – Specifies the number of scatter bounces. The actual number of scatter bounces computed is still limited by the number of diffuse bounces set in the scene/renderer settings. Setting the number of scatter bounces to a negative value is equivalent to using the scene/renderer diffuse bounces limit.