This page provides information on the BRDFVRayMtl which is the basis for most shading networks in V-Ray.

 

Overview


The BRDFVRayMtl node is a very versatile material that allows for better physically correct illumination (energy distribution) in the scene, faster rendering, and more convenient reflection and refraction parameters. This material can be easily set up to simulate a huge variety of surfaces from plastics to metals to glass and more by adjusting a handful of parameters.

Furthermore, with the BRDFVRayMtl you can apply different texture maps, control the reflections and refractions, add bump and displacement maps, force direct GI calculations, and specify the BRDF type for determining how light interacts with the material.

 

UI Paths


 ||mat Network|| > V-Ray > Material > V-Ray Material

||out Network|| > V-Ray Render Elements node > V-Ray > Material > V-Ray Material

 


Node


The V-Ray BRDFVRayMtl provides inputs for controlling various material properties. They correspond to parameters in the section below.

 

 

Diffuse



 

 

Color – Specifies the diffuse color of the material. Note: the actual diffuse color of the surface also depends on the reflection and refraction colors.

Roughness – Specifies the roughness of the diffuse part of the material. Used to simulate rough surfaces or surfaces covered with dust (for example, skin, or the surface of the Moon).

Roughness Model Specifies the Roughness model.

Oren-Nayar A reflectivity model for diffuse reflection from rough surfaces that has been shown to accurately predict the appearance of a wide range of natural surfaces. We recommend using this roughness model.
Gamma-based  The roughness model used in previous versions of V-Ray. This is not the recommended option.

Opacity – Assigns opacity to the material where 1.0 is completely opaque and 0.0 is completely transparent.

Opacity Mode – Controls how the opacity map works.

Normal –  The opacity map is evaluated as normal: the surface lighting is computed and the ray is continued for the transparent effect. The opacity texture is filtered as normal.
Clip – The surface is shaded as either fully opaque or fully transparent depending on the value of the opacity map (i.e. without any randomness). This mode also disables the filtering of the opacity texture. This is the fastest mode, but it might increase flickering when rendering animations.
Stochastic – The surface is randomly shaded as either fully opaque or fully transparent so that on average it appears to be with the correct transparency. This mode reduces lighting calculations but might introduce some noise in areas where the opacity map has gray-scale values. The opacity texture is still filtered as normal.

Self-illumination – Specifies the self-illumination color of the material.

Self-illumination Mult. – Specifies a multiplier for the self-illumination of the material.

Self-illumination Affects Gi – When enabled, the self-illumination color affects GI computations.


Reflection





Brdf Type – Determines the type of BRDF (the shape of the highlight and glossy reflections). This parameter has an effect only if the Reflection Color is different from black and Reflection Glossiness is different from 1.0. For more information, see The BRDF Type example below.

Phong – Phong highlight/reflections
Blinn – Blinn highlight/reflections
Ward – Ward highlight/reflections
GGX – GGX Microfacet highlight/reflections

GGX is the most modern and flexible BRDF (Bidirectional reflectance distribution function) type and is able to better represent a broad range of materials thanks to its ability to control the shape of the specular lobe.

There currently isn't any particular performance difference between models and there is little reason to choose any of the other types.

 Read more...

Historically, the Phong, Blinn, Ward and GGX are successive reflectance models developed over the years in computer graphics where each model aimed to improve on the limitations of the previous ones. For example, the specular highlights with the Phong model have a very narrow and bright center with no falloff, but it doesn't work well with anisotropic reflections. The Blinn model has broader highlight center with a tight falloff. The Ward model has an even broader center and falloff. The GGX model has a bright center and an even longer falloff (at default settings). In the past, each model's characteristics resembled more closely a certain type of material, for example Phong could be used for plastics, Ward for cloth and metals, and Blinn for other common surfaces. However with the introduction of the GGX model, all of these surfaces can be approximated well, thus reducing the need for using the other models.

It should be noted that no principled model is able to represent all possible materials entirely accurately, and where those models fail - for example when the material isn’t viewed frontally - only approaches such as that of VRscans are able to capture the correct material representation.

GGX Tail Falloff – Controls the transition from highlighted areas to non-highlighted areas when the BRDF Type is set to GGX.

Color – Reflection color. Note that the reflection color dims the Diffuse Color. For more information, see The Reflection Color Parameter example below.

Glossiness – Controls the sharpness of reflections. A value of 1.0 means perfect mirror-like reflection; lower values produce blurry or glossy reflections. Use the Reflection Subdivs parameter below to control the quality of glossy reflections. For more information, see The Reflection Glossiness Parameter example below.

Use Fresnel – When enabled, makes the reflection strength dependent on the viewing angle of the surface. Some materials in nature (glass etc) reflect light in this manner. Note that the Fresnel effect depends on the index of refraction (IOR) as well.

Glossy Fresnel – When enabled, uses glossy fresnel to interpolate glossy reflections and refractions. It takes the Fresnel equation into account for each "microfacet" of the glossy reflections, rather than just the angle between the viewing ray and the surface normal. The most apparent effect is less brightening of the grazing edges as the glossiness is decreased. With the regular Fresnel, objects with low glossiness may appear to be unnaturally bright and "glowing" at the edges. The Glossy Fresnel calculations make this effect more natural.

Lock Fresnel IOR to Refraction IOR – Allows the user to unlock the Fresnel IOR parameter for finer control over the reflections. When this is enabled, the Fresnel IOR is locked to the Refraction IOR.

Fresnel IOR – The IOR to use when calculating Fresnel reflections. Normally this is locked to the Refraction IOR parameter, but you can unlock it for finer control. For more information, see The Use Fresnel Option example below.

Metalness – Controls the reflection model of the material from dielectric (metalness 0.0) to metallic (metalness 1.0). Note that intermediate values between 0.0 and 1.0 do not correspond to any physical material. This parameter can be used with PBR setups coming from other applications. The reflection color should typically be set to white for real world materials.

Subdivs – Controls the quality of glossy reflections. Lower values render faster, but the result is more noisy. Higher values take longer, but produce smoother results. Note that this parameter is available for changing only when Use Local Subdivs is enabled in the DMC Sampler.

Anisotropy – Determines the shape of the highlight. A value of 0.0 means isotropic highlights. Negative and positive values simulate "brushed" surfaces. For more information, see the Anisotropy example below.

Rotation – Determines the orientation of the anisotropic effect in a float value between 0 and 1 (where 0 is 0 degrees and 1 is 360 degrees). For more information, see Anisotropy Rotation example below.

Uv Vectors Derivation – Specifies the method for deriving anisotropy axes:

Local Axis – Uses a local axis for the anisotropy effect.
UVW Generator – Allows the user to assign a UVW Generator for the anisotropy effect.

Axis – Specifies a local object axis for the anisotropy effect when Uv Vectors Derivation is set to Local Axis.

Trace Reflections – Enables reflections for the material.

Exit Color – If a ray has reached its maximum reflection depth, this color is returned without tracing the ray further.

Max Depth – The number of times a ray can be reflected. Scenes with lots of reflective and refractive surfaces may require higher values to look correct.

Enable Dim Distance – Enables the Dim distance parameter which allows you to stop tracing reflection rays after a certain distance.

Dim Distance – Specifies a distance after which the reflection rays are not traced.

Dim Fall-off – A fall off radius for the dim distance.

Soften – Softens the edge of the BRDF at light/shadow transitions

Affect Channels – Allows the user to specify which channels are going to be affected by the reflectivity of the material.

Color Only – The reflectivity affects only the RGB channel of the final render.
Color+alpha – Causes the material to transmit the alpha of the reflected objects, instead of displaying an opaque alpha.
All channels – All channels and render elements are affected by the reflectivity of the material.

 


 

Example: The BRDF Type


This example demonstrates the differences between the BRDFs available in V-Ray. Note the different highlights produced by the different BRDFs. The Reflection Glossiness is set to 0.8.

 

BRDF type is Phong

BRDF type is Blinn

BRDF type is Ward

 BRDF type is GGX

 

 


 

Example: The Reflection Color Parameter


This example demonstrates how the Reflection color parameter controls the reflectivity of the material. Note that this color also acts as a filter for the diffuse color (e.g. stronger reflections dim the diffuse component). Use Fresnel is disabled.

 

Reflection color is black (0, 0, 0)

Reflection color is medium gray (128, 128, 128)

Reflection color is white (255, 255, 255)

 

 


 

Example: The Reflection Glossiness Parameter


This example demonstrates how the Reflection glossiness parameter controls the highlights and reflection blurriness of the material. The Reflection Color is white and Use Fresnel is enabled.

 

Reflection Glossiness is 1.0 (perfect mirror reflections)

Reflection Glossiness is 0.8

Reflection Glossiness is 0.6

1
0.6

 

 


 

Example: The Use Fresnel Option


This example demonstrates the effect of the Use Fresnel option. Note how the strength of the reflection varies with the IOR of the material. For this example, the Reflection color is pure white (255, 255, 255).

 

Fresnel is off

Fresnel is on, IOR is 1.3

Fresnel is on, IOR is 2.0

Fresnel is on, IOR is 10.0

Off
10.0

 

 

 


Example: The Anisotropy and Rotation Parameters

 

This example demonstrates the effect of the Anisotropy and Rotation parameters, which determines the shape of the highlight. For the examples below the Type was set to Microfacet GTR (GGX).


Anisotropy = -0.8


Anisotropy = -0.6


Anisotropy = -0.4

Anisotropy = -0.2


Anisotropy = 0.0


Anisotropy = 0.2


Anisotropy = 0.4


Anisotropy = 0.6


Anisotropy = 0.8

-0.8
0.8


Rotation = 0


Rotation = 18


Rotation = 36


Rotation = 54


Rotation = 72


Rotation = 90


Rotation = 108


Rotation = 126

Rotation = 144

Rotation = 162


Rotation = 180

0
180

Refraction




Color – Refraction color. Note that the actual refraction color depends on the Reflection Color as well. For more information, see The Refraction Color Parameter example below.

Glossiness – Controls the sharpness of refractions. A value of 1.0 means perfect glass-like refraction; lower values produce blurry or glossy refractions. Use the Refraction Subdivs parameter below to control the quality of glossy refractions. For more information, see The Refraction Glossiness Parameter example below.

Index of Refraction – Index of refraction for the material, which describes the way light bends when crossing the material surface. A value of 1.0 means the light does not change direction.  For more information, see The Refraction IOR Parameter example below.

Subdivs – Controls the quality of glossy refractions. Lower values render faster, but the result is more noisy. Higher values take longer, but produce smoother results. Note that this parameter is available for changing only when Use Local Subdivs is enabled in the DMC Sampler.

Fog Color – The attenuation of light as it passes through the material. This option helps simulate the fact that thick objects look less transparent than thin objects. Note that the effect of the fog color depends on the absolute size of the objects and is therefore scene-dependent. This parameter can be mapped with a texture. It is recommended that you use a 3D texture for the purpose. For more information, see the Fog Color Parameter example below. 

Fog Multiplier – The strength of the fog effect. Smaller values reduce the effect of the fog, making the material more transparent. Larger values increase the fog effect, making the material more opaque. For more information, see The Fog Multiplier Parameter example below.

Fog Bias – Changes the way the fog color is applied. Negative values make the thin parts of the objects more transparent and the thicker parts more opaque and vice-versa (positive numbers make thinner parts more opaque and thicker parts more transparent).

Fog Units Scaling – Enables unit scale multiplication when calculating absorption.

Dispersion – Enables the calculation of true light wavelength dispersion.

Abberation – Allows the user to increase or decrease the dispersion effect. Lowering it widens the dispersion and vice versa.

Affect Shadows – This parameter causes the material to cast transparent shadows to create a simple caustic effect dependent on the Refraction Color and the Fog Color. For accurate caustic calculations, disable this parameter and instead enable Caustics in the V-Ray Renderer. Simultaneous usage of both Caustics and Affects Shadows can be used for artistic purposes but does not produce a physically correct result.

Trace Refractions – Enables refractions for the current material.

Use Exit Color – Enables the use of Exit Color.

Exit Color – If a ray has reached it's maximum depth this color is returned instead of tracing the ray further

Max Depth – The number of times a ray can be refracted. Scenes with lots of refractive and reflective surfaces may require higher values to look correct.

Affect Channels – Allows the user to specify which channels are going to be affected by the transparency of the material

Color Only – The transparency affects only the RGB channel of the final render.
Color+alpha – This causes the material to transmit the alpha of the refracted objects, instead of displaying an opaque alpha.
All channels – All channels and render elements are affected by the transparency of the material.

 

 


 

Example: The Refraction Color Parameter


This example demonstrates the effect of the Refraction color parameter to produce glass materials. For the images in this example, the material is with a grey Diffuse color, white Reflection color and Fresnel option on.

 

Refraction color is black (0, 0, 0) (no refraction)

Refraction color is light grey (192, 192, 192)

Refraction color is white (255, 255, 255)

 

 


 

Example: The Refraction IOR Parameter


This example demonstrates the effect of the Refraction IOR parameter. Note how light bends more as the IOR deviates from 1.0. The case when the index of refraction (IOR) is 1.0 produces a transparent object. Note however, that in the case of transparent objects, it might be better to assign an opacity map to the material, rather than use refraction.

 

Refraction IOR is 0.8

Refraction IOR is 1.0

Refraction IOR is 1.3

Refraction IOR is 1.8

0.8
1.8

 

 


 

Example: The Refraction Glossiness Parameter


This example demonstrates the effect of the Refraction glossiness parameter. Note how lower Refraction glossiness values blur the refractions and cause the material to appear as frosted glass.

 

Refraction glossiness is 1.0

Refraction glossiness is 0.9

Refraction glossiness is 0.8

1.0
0.8

 


 


 

Example: The Fog Color Parameter


This example demonstrates the effect of the Fog color parameter. Notice how the thick areas of the object are darker in the two images on the right because of the light absorption of the fog.

 

Fog Color is White (255, 255, 255)

Fog Color is Gray (243, 243, 243)

Fog Color is Green (230, 243, 213)

 

 


 

Example: The Fog Multiplier Parameter


This example demonstrates the effect of the Fog multiplier parameter. Smaller values cause less light absorption because of the fog; while higher values increase the absorption effect.

 

Fog multiplier is 0.3

Fog multiplier is 1.0

Fog multiplier is 1.5

0.3
1.5

 


Translucency




Translucency Type – Selects the algorithm for calculating translucency (also called sub-surface scattering). Note that refraction must be enabled for this effect to be visible. Currently only single-bounce scattering is supported. See the example below for illustration. 

None – No translucency is calculated for the material.
Hard (wax) model – This model is specifically suited for hard materials like marble.
Soft (water) model – This model is mostly for compatibility with older V-Ray versions (1.09.x).
Hybrid model – This is the most realistic SSS model and is suitable for simulating skin, milk, fruit juice and other translucent materials.

Color – Normally the color of the sub-surface scattering effect depends on the Fog color; this parameter allows you to additionally tint the SSS effect.

Fwd / Back coeff – Controls the direction of scattering for a ray. A value of 1.0 means a ray can only go forward (away from the surface, inside the object); 0.5 means that a ray has an equal chance of going forward or backward; 0.0 means a ray is scattered backward (towards the surface, to the outside of the object).

Light Multiplier – Specifies a multiplier that controls the strength of the translucent effect.

Scatter Coeff – The amount of scattering inside the object. A value of 1.0 means rays are scattered in all directions; 0.0 means a ray cannot change its direction inside the sub-surface volume.

Maximum Thickness – Limits the rays that are traced below the surface. This is useful if you do not want or don't need to trace the whole sub-surface volume.

 


 

Example: Translucency Type

 

This example demonstrates the effect of the Translucency type parameter. Note that refraction must be enabled for this effect to be visible. Currently, only single-bounce scattering is supported. The Diffuse is red (0.9;0.225;0) and the Translucency Color is blue(0; 0; 0.9); Refraction color (0.822; 0.822; 0.822) and Fog Color(0.697; 0.697; 0.697) are set to light gray.

 

None

Hard (Wax) model

Soft (Water) model

Hybrid model

 

 


Options


 

 

Cutoff – A threshold below which reflections/refractions is not traced. V-Ray tries to estimate the contribution of reflections/refractions to the image, and if it is below this threshold, these effects are not computed. Do not set this to 0.0 as it may cause excessively long render times in some cases.

Double-sided – When enabled, V-Ray flips the normals for back-facing surfaces with this material assigned. Otherwise, the lighting on the "outer" side of the material is computed always. You can use this to achieve a fake translucent effect for thin objects like paper.

Reflect On Back Side – When disabled, V-Ray calculates reflections for the front side of objects only. Checking it makes V-Ray calculate the reflections for the back sides of objects too.

Use Irradiance Map – When enabled, the irradiance map is used to approximate diffuse indirect illumination for the material. If disabled, Brute Force GI is used in which case the quality of the Brute force GI is determined by the Subdivs parameter of the Irradiance Map. This can be used for objects in the scene which have small details that are not approximated very well by the irradiance map.

Energy Preservation – Determines how the diffuse, reflection, and refraction color affect each other. V-Ray tries to keep the total amount of light reflected off a surface to less than or equal to the light falling on the surface (as in the real life). For this purpose, the following rule is applied: the reflection level dims the diffuse and refraction levels (a pure white reflection will remove any diffuse and refraction effects), and the refraction level dims the diffuse level (a pure white refraction color will remove any diffuse effects). This parameter determines whether the dimming happens separately for the RGB components or is based on the intensity:

Monochrome – Causes dimming to be performed based on the intensity of the diffuse/reflection/refraction levels.
Color
– Causes dimming to be performed separately on the RGB components. For example, a pure white diffuse color and pure red reflection color will yield a surface with a cyan diffuse color (because the red component is already taken by the reflection).

Glossy Rays As GI – Specifies on what occasions glossy rays are treated as GI rays:

Never – Glossy rays are never treated as GI rays.
GI Rays – (Default) Glossy rays are treated as GI rays only when GI is being evaluated. This can speed up rendering of scenes with glossy reflections.
Always – Glossy rays are always treated as GI rays. A side effect is that the Secondary GI engine is used for glossy rays. For example, if the primary engine is irradiance map and the secondary is light cache, the glossy rays uses light cache (which is a lot faster).

Refl. Gloss. Interpretation –These options control how Reflection Glossiness is interpreted. When Use Glossiness is selected, the Glossiness value is used as is, and a high Glossiness value (such as 1.0) results in sharp reflection highlights. When Use Roughness  is selected, the Reflection Glossiness  inverse value is used. For example, if Reflection Glossiness  is set to 1.0 and Use Roughness  is selected, this results in diffuse shading. Conversely, if Glossiness is set to 0.0 and Use Roughness is selected, this results in sharp reflection highlights. Note that the Roughness parameter itself has no bearing on the results of this option. 

Use Environment Override – Enables the use of the Environment Override color.

Environment Override – A color or texture that is used as an environment for the material.

Environment Priority – Specifies the environment override priority when several materials override it along a ray path.