Houdini 16.5 Nodes VOP nodes

Trace VOP node

Uses the vex gather function to send a ray and return with the reflected or refracted colors.

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This is the origin of the ray, typically the surface point being shaded, P.


This is the surface normal. It should be normalized, if explicitly connected as an input. Implicitly, the normalized global variable, N, is used. Frontface should not be used on normals with the trace vop.

Ray Type

The type of rays to send out,reflect or refract. Mantra will use one of three different hard limits for ray bounce determination based on this value.

Trace Intensity

This should be multiplied times either the reflection intensity, Kr or the transmission intensity, Kt, (depending on the ray type) result from the Fresnel vop. This gives the user some additional control to dim or brighten the resultant trace color.

Trace Vector

This is the initial direction for the ray to follow . Usually this vector, like Kt above, is either the reflection vector, R, or the transmission vector, T, (depending on the ray type) result from the Fresnel vop. The reflection ray can be derived from

dir = reflect(nI,nN)
and the incident vector, I, can be substitued for the transmission ray if eta is not a factor.

Trace Tint

A color used to tint the resultant trace color.

Environment Map

The color from this environment map is returned if the ray does not hit anything. Without a map here, the Background Color, below, is returned when the ray misses.

It is recommended to have some map in this slot. The background image as a texture is a good choice to start.

Background Color

This color is returned when the ray does not hit anything and there is no environment map specified.

Ray Bias

This is typically a small number used to help solve self-intersection issues.

Jitter Amount

This is a value between 0, no jitter and 1, maximum jitter. It controls how randomly the samples are distributed.


The number of rays to send. The more ray sent, the better the quality, the slower the render.

Cone Angle

The rays are distributed over a cone defined by this angle (in degrees). The default is 0, no blur.

Attenuation Density

Attenuation distance.

Attenuation Color

Attenuation color



The trace color times Kt and the Tint Color.


The PBR trace calculation times Kt and the Tint Color.

VOP nodes