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Selection Expressions

An operator can use a selection to determine what nodes will be selected to be processed by the operator at render time. The selection is an expression that can consist of multiple selections concatenated by:

  • or (union)
  • and (intersection)
  • not (negation)
  • and not (exclusion)
  • () for nested scoping


Each selection uses glob patterns and regular expressions and a node will be processed by the operator if the expression matches the node name. By default glob matching is used unless the selection is in a regex quote, i.e. r'<my_regex>'. Here are a few examples:

Code Block
(/group0/sphere* and not (/group0/sphere1 or /group0/sphere0)) or /group1/sphere3
not r'p(ickle|ringle)[0-9]+'
r'c(ar1|ar2)' or r'car[34]'


(/group0/sphere* and not (/group0/sphere1 or /group0/sphere0)) or /group1/sphere3

not r'p(ickle|ringle)[0-9]+'

r'c(ar1|ar2)' or

Parameter Matching

Selections can also be used to match parameter names and values on the selected nodes, including the node entry name, type, and derived type. This is done using a parameter dot-delimiter .() on each node selection string. The following example selection matches all nodes named 'sphere' which have a 'radius' parameter.

  • sphere.(radius)


Comparators can be used to match certain parameter values. The following selection matches all nodes whose name starts with 'sphere' and has a 'radius' larger than 0.5.

  • sphere*.(radius > 0.5)

The parameter matching also supports concatenation and glob/regex, e.g.

  • car*.((make == 'fiat' and year > 2010) or tinted_glass == True) or drone*.(battery_level >= 20)
  • plane*.(model == 'A3*' and captain == r'B(ob|ryan)')

Arrays and Multi-Value Parameters

Arrays and multi-value parameters such as vectors, RGB, etc. are matched using square brackets. If an array has a single value or if the array consists of single numbers then only one set of square brackets is necessary.

  • *.(rgb_array == [[1 2 3][4 5 6]])
  • *.(float_array == [10.0 20.0 30.0])
  • *.(velocity >= [1.0 1.0 1.0])
  • *.(my_matrix == [1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6])

String Literals

Matching parameters of type string, enum and node requires string literals, e.g.

  • *.(some_string == '*value*')
  • *.(transform_type == 'rotate_about_center')
  • *.(shader == 'purple_shader')
  • *.(shader == 'yellow_*')


Note: The value will be treated as a parameter reference if the string quotes are omitted (see below).

Parameter Array Indices

It is possible to match specific array indices in array and multi-value parameters. Square brackets are not necessary when matching a single value.

  • *.(accessories[3] == 'monkey fists')
  • *.(my_rgb[1] == 1.0)
  • *.(rgb_array[1] >= [0 0 0])
  • *.(float_array[1] == 20.0)
  • *.(rgb_array[1]) # checks if the entry exists 

Matching Parameter References

Commonly, the node already has some arbitrary user parameters coming from e.g. simulation or even another operator.

It is possible to match other node parameters of the same type, e.g.

  • *.(radius <= some_float_param)
  • *.(my_rgb == some_rgb_param)


Node parameters can match single string values, e.g. to match a shader based on a user string parameter

  • *.(shader == some_string)


We can also match parameters on other nodes, where the syntax is #node_name.param_name1[.param_nameN]

  • *.(model == #some_node.model)
  • *.(year == #some_node.some_int)
  • *.(year == #some_node.node_array[0].year)
  • *.(my_rgb == #some_node.some_rgb)


It can be useful to match values on parameters that are linked to the node. Shaders are a common example, where the value can also refer to other parameters

  • *.(shader.base == 0.8)
  • *.(shader.base_color == [1 1 0])
  • *.(shader[0].base_color.filename == '*plate*')
  • *.(shader[0].base_color.filename == #some_node.tex_name)


Matching Multiple Parameter Names

We can also match more than one parameter by using a glob or regex expression in the parameter name.

A simple example is matching an RGB parameter regardless of if it's called color or colour.

  • *.(colo*r == [1 0.4 0.2])
  • *.(mod* == r'(X|M)[0-9]')
  • *.(r'receive_sha.*' == True)


The operator is given all the parameters that matched where it can either use all of them or decide what to do with each one.

Matching Node Entries

The selection can filter based on node entry information such as node entry name (@node), type (@type), and derived type (@derived)

  • *.(@node == 'polymesh')
  • *.(@type == 'shape')
  • *.(@derived == 'procedural')


This can be concatenated in the usual way with other parameter selections.

  • *.(@node == 'sphere' and radius > 0.4)



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