wrlparser

Python library to parse VRML files (.wrl) using an LALR parser with a Context-Free Grammar.

Getting started

Installing

pip install wrlparser

Sample program

This program parses the file which name has been given as a command line argument. Two sample models have been provided in the tests/models folder.

from wrlparser import parse
import sys

file = sys.argv[1]
with open(file) as f:
    l = "".join(f.readlines())
    f.close()

scene = parse(l)

Documentation

Context-Free Grammar

This parser is based on the grammar provided by the VRML97 specification. The grammar described in the specification is a Context-Sensitive Grammar which isn't deterministic. The following changes have been made to make it a Context-Free Grammar.

• Recursive rules have been generalized to allow collections to be empty as this will resolve shift/reduce conflicts. This should only broaden the spectrum of parsable files.

elements : element                  elements : element elements
         | element elements    ->            | empty      
         | empty                     

• IDs have been optimized to the raw ID type

• Field values have been optimized to the raw type

sffloatValue :
sfcolorValue :
sfvec2fValue :  ->  sffloatValues : FLOAT sffloatValues
sfvec3fValue :                    | empty
...

Intermediate Representation (IR)

Once parsed, the file's content is returned to the user as classes. Their structure strictly corresponds to the one described in the specification.

For instance, a material node has the following fields :

  - ambientIntensity : float
  - diffuseColor     : list[3]
  - specularColor    : list[3]
  - emissiveColor    : list[3]
  - transparency     : float
  - shininess        : float

It should be noted that the specification doesn't require a file to specify every field of a node. They should therefore be check before accessed as follows:

m = Material()
if m.ambientIntensity != None:
  # Use the value

Tests

This parser has been tester with models from the KiCad catalog.

Issues

Even though the parser fully supports VRML's grammar, a very small subset of the intermediate representation has been implemented. This is due to the lack of test models for specific node types.

If you every need to parse a file which has an unimplemented feature, feel free to share the file in a ticket so that I can support it.