This page provides information on the Fire tab parameters of the V-Ray PhxShaderSim node.
Overview
This tab controls the emissive (fire) color of the volumetric shader. There are controls for the color and intensity of the emission as well as for gradual transition between a physically correct and artistic look of the fire. Unlike the smoke color which needs an external light to become visible, fire will be visible immediately.
All Fire Lights options are ignored when rendering with V-Ray GPU. Enable Global Illumination from the V-Ray Settings if you need the Smoke and/or the scene to be illuminated by the fire.
Intensity/Color
Scale – General multiplier for the fire intensity.
Physically Based – Transitions between artistic look of the fire (when set to 0) and realistic physically based Intensity (when set to 1). The realistic mode multiplies the fire intensity by the Black Body Radiation model, which gives strong brightness to the hot parts of the fire. The example below uses the settings from the miniature image on the right. For more information, see the Physically Based example below.
The Physically Based option expects the range of the emission field to be representative of the real-world Black Body Radiation curve, in Kelvins. To get physically-accurate emission, use a Volume Wrangle SOP to remap the emission field to the range of e.g. 400-3000 prior to caching to disk. For example, the following snippet will remap the heat field from 0-2 to 400-3000:
f@heat = 400 + fit(@heat, 0, 2, 0, 2600);
Opacity
Mode – While smoke has its own opacity in the Smoke tab, fire opacity can be determined in one of these ways:
Use Smoke Opacity – Fire uses the same opacity set for smoke in the Smoke tab. This way the fire is not visible in cells where there is no smoke.
Fully Visible – Fire always uses opacity of 1.0, regardless of the smoke's opacity.
Use Own Opacity – A varying opacity can be set for the fire using the Opacity curve.
Multiplier – General multiplier for the fire opacity.
Texture Mode – If set to Multiply Opacity by Texture or Fire Opacity from Texture, this slot specifies the texture used to modulate the Fire Opacity.
Intensity and Color
Source Range – Specifies the range of the fire intensity and color.
Intensity Ramp – A gradient ramp for the fire intensity.
Color Ramp – A gradient ramp for the fire color.
Example: Physically Based
This example illustrates transitioning from a darker artistic look (0) to a photorealistic look (1) using the Physically Based parameter to alter the apparent brightness of the fire.
Physically Based = 0
Physically Based = 0.1
Physically Based = 1