Houdini 20.5 Nodes Geometry nodes

Labs Physical Ambient Occlusion 1.1 geometry node

Computes ambient occlusion, generates dirt masks, as well as identifies peaks and valleys on meshes.

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Since 19.5

This node can perform 4 types of mesh analysis akin to the concept of ambient occlusion. The Physical Ambient Occlusion mode is more physically-grounded. The Valleys, Peaks, and Dirt Buildup modes have more artistic interpretations.

When computing ambient occlusion, this node uses high-frequency icosahedral sampling. This new method is more efficient and stable compared to the classical random-direction sampling. Icosahedral samples have much more uniform distributions. It also eliminates the need for a random seed parameter, making the controls more intuitive, as it is perhaps more natural to think of ambient occlusion as being intrinsic to the mesh rather than dependent upon a random factor.

For this same reason, the icosahedral sampling method is also used to identify peaks and valleys.

Dirt mask generation still uses random-direction sampling because the visual noise in this case is desired.

Parameters

Mode

The type of mesh analysis to perform.

Physical Ambient Occlusion: Computes ambient occlusion using a physically-plausible weighting scheme.

Valleys: Identifies areas with high concavity. The valley areas have lower output values.

Peaks: Identifies areas with high convexity. The peak areas have higher output values.

Dirt Buildup: Creates a dirt mask somewhat similar to ambient occlusion but algorithmically more noisy and random.

Sample Frequency

The frequency of the class I icosahedral geodesic polyhedra used to generate the ambient occlusion samples.

Sample Count

The number of random-direction samples.

Neighbourhood Radius

The radius of the neighbourhood to take into account when generating the results. In other words, it is the maximum trace distance of each sample.

Visibility Exponent

Visually affects the contrast of the output values. The contribution of each sample hit is weighted by the distance of the hit relatively to the maximum trace distance. The further away the hit is, the less it contributes to the weighted sum. This parameter controls how drastic that contribution fall-off is. The default value of 0.5 has a physically-plausible explanation.

Random Seed

The seed used to generate the random sample directions.

Blurring Iterations

The number of times the output values are blurred.

Blurring Step Size

The blurring amount in each iteration. Lower step sizes combined with higher blurring iterations can better retain large-scale variations while smoothing out small-scale variations.

Output Attribute

The name of the output attribute. This attribute’s meaning depends on which Mode is selected.

Normalize Output

Normalizes the output values to 0-1 range.

Invert Output

Outputs one minus the original output values.

Remap Output

Remaps the output values.

Remap Ramp

Controls how the output values are remapped.

Visualize Output

Adds a color attribute to visualize the output values.

Visualization Ramp

Controls how the output values are visualized.

Advanced

Cone Axis

Selects what to use as the central axis of the sampling cone.

Half-Cone Angle

In degrees, the limiting angle between any sample direction and the cone axis.

Ray Offset

Offsets the trace origin of each sample from the mesh surface in the direction of the cone axis by this amount. This is typically used to prevent false hits.

Visualize Samples (Slow)

Creates polylines on each point to visualize all the samples. This is very slow and mostly for debug purposes.

Sample Display Scale

Scales down the visualized trace distance to avoid visual chaos. When this is set to 1, the length of the visualized samples matches the value of Neighbourhood Radius.

Examples

Geometry nodes