Houdini 20.0 Nodes VOP nodes

PBR Metallic Reflection VOP node

Computes metallic reflections.

Since 16.0


Specular Model

The mathematical model used to simulate glossy reflections. For each viewing angle and surface normal, the model defines from which directions and at what intensity light is reflected. This is what shapes specular highlights and reflections in general.

The overall glossiness, and with it the size of highlights, is controlled by Roughness. The available models simulate the effects caused by Roughness with varying degrees of physical accuracy, with GGX currently being the most accurate.

The chosen model has no effect when Roughness is 0, since this causes light to be reflected from a single direction at full intensity, making the model irrelevant.

See Roughness for more information.

Component Label

Specifies a label for the metallic reflection BSDF. This can be used to export contributions from this component to a separate image plane.


Controls the reflectivity of surfaces facing the viewer.

When a surface is rotated away from the viewer, more and more light is reflected regardless of this parameter’s value. At 90 degrees away from the viewer, 100% of the light is reflected, as in the real world.


How shiny an object appears mostly depends on its Roughness rather than its Reflect value. When you intend to vary shininess using a texture, Roughness is usually the better parameter to use.


For additional artistic control, you can disable reflections completely by setting Reflect exactly to 0.0. When using a texture, this effect also occurs in completely black areas of the texture.


Controls how dull a surface appears. A value of 0.0 results in a smooth surface with perfectly sharp reflections. A value of 1.0 produces a completely dull surface.

This simulates microscopic bumps which become more pronounced the higher the Roughness, causing reflected light to be scattered more.


Causes reflections to be stretched in the direction defined by Anisotropy Direction.

This simulates microscopic bumps with a directional bias, causing light to be scattered more in the defined direction. This is typical of brushed metals.

The effect of this parameter increases with Roughness. It has no effect at all when Roughness is 0.0.

Anisotropy Direction

Controls the direction of Anisotropy relative to the UV coordinates of the surface. At 0.0, reflections are stretched in the U direction. At 0.5, the direction is rotated by 90 degrees to the V direction. 1.0 equals 180 degrees. Since the effect is symmetrical this produces the same result as 0.0.

The direction of rotation also depends on the UV layout. When the UVs are layed out such that textures appear on the surface without mirroring, higher values rotate counter-clockwise.

The effect of this parameter diminishes with decreasing Roughness and Anisotropy.

This parameter has its own Filter Type parameter which appears when Use Texture is enabled. This defaults to Point (No Filter), which usually works best. When you change this to an actual filter like Gaussian, artifacts may appear around the transition between areas with different direction values.


The 0-1 range makes it easy to apply a texture to this value. To find the texture value needed for a certain direction:

  • Turn off Use Texture under Anisotropy Direction.

  • Try out values on the slider and kick off test renders until you get the desired result.

  • Paint the slider value into your texture.

  • Turn Use Texture back on.

To help with this workflow, the Anisotropy Direction remembers its value whenever Use Texture is toggled. It defaults to 1.0 when Use Texture is enabled, meaning you get the unmodified texture data.

Shade Both Sides As Front

Shades both sides of the surface as if they were the front.

See also

VOP nodes