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It’s often useful to assign different materials across a large number of objects, to create a more natural look.
This node lets you assign materials randomly, or “spatially”, so clumps of prims tend to get the same material.
When using “weighted random”, any materials listed in Materials but not in the multi-parm are considered to have a weight of 1.
The primitive(s) the node should operate on. You can drag primitives from the scene graph tree pane into this textbox to add their paths, or click the Reselect button beside the text box to select the primitives in the viewer, or ⌃ Ctrl-click the Reselect button to choose prims from a pop-up tree window. You can also use primitive patterns for advanced matching, including matching all prims in a collection (using
The material prims to choose from. You can use primitive patterns, including matching all prims in a collection (using
The seed value for random material selection. Changing this changes the “random” choices generated. You can use this to try different variations, or change the random choices over time.
How to choose materials for each selected prim.
Choose materials at random. You can use the Bias ramp to influence the distribution.
Assign materials in Voronoi noise-based “clumps”, so prims in close proximity often get the same material.
Like “Random”, but lets you assign weights to each material, so some materials are chosen more often than others.
When Method is “Random”, the horizontal axis is divided between the materials to choose from. At the center of a horizontal segment corresponding to a certain material, the height of the ramp is the percentage chance of that material being chosen. Set the Interpolation to “constant”.
For example, given 3 materials, to give the second material a 50% chance of being assigned, add a point at position 0.25, with a value of 0.5, set the last point’s position to 0.75 with a value of 1.
If the probabilities don’t add up to exactly 100% the values are normalized.
This ramp might be useful to interactively play with material probabilities, however if you want to assign specific probabilities to specific materials, it’s much easier to use the “Weight Random” Method.
Spatial distribution settings
These parameters are shown when Method is “Spatial distribution”
Whether to specify the time at which to measure the prim positions in frames or by seconds.
Measure the positions of the prims at this frame number.
Rounds the given frame number to the nearest integer frame, avoiding fractional frame cooking.
Measure the positions of the prims at this number of seconds along the timeline.
Controls the size of the voronoi cells. A higher frequency will generate smaller cells.
Moves the noise through 3D.
Lower values give more even cells, higher values give more variation between large cells and small cells.
The node applies anti-aliased noise to each primitive’s centroid before passing it to the Voronoi function. This helps break up the otherwise regular edges from the Voronoi cellular pattern.
The frequency of anti-aliased noise used to jitter primitive positions.
Scales anti-aliased noise used to jitter primitive positions.
Coarseness of the noise used to jitter primitive positions.
Maximum number of iterations of noise to apply when jittering primitive positions.
Weighted random settings
Creates multi-parm instances for each material selected in the Materials field. If you change the Materials pattern and want to re-do this, click Clear in the multi-parm, then click this button again.
For each material, whether to assign it a weight.
Scene graph path to the material prim. If this material doesn’t exist, or isn’t listed in Materials, the node ignores it.
A weighting factor to assign to the material. Materials with higher weights are more likely to be chosen. The node normalizes the weights, so they are all relative to each other.
Note that materials listed in Materials but not in the multi-parm are considered to have a weight of