94 lines
3.6 KiB
Markdown
94 lines
3.6 KiB
Markdown
# vrml1to97
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JavaScript converter from VRML 1.0 to VRML97 file format.
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This converter was originally a JavaScript reimplementation of the algorithm
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of the "token rearranger" found in the
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[Wings 3D x3d importer](https://github.com/dgud/wings/blob/master/plugins_src/import_export/x3d_import.erl)
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(which was written in Erlang).
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However, from version 0.3, it adds support for a significantly larger subset of
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VRML 1.0. Overall, it recognizes and converts
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* Title, SceneInfo, BackgroundColor, and View "Info" nodes [this node type
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was removed in VRML97].
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* All Light nodes
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* PerspectiveCamera nodes (converted into Viewpoint nodes)
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* Grouping nodes including Separator, Group, Switch, and WWWAnchor
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* Interprets a Switch named "Cameras" (by a DEF) as a list of Viewpoints
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* ShapeHints
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* Transformation nodes including Translation, Rotation, Scale, and Transform
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* All shape nodes including Cube, Cone, Cylinder, Sphere, IndexedFaceSet,
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IndexedLineSet, PointSet, Coordinate3, and Normal
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* All material nodes including Material, TextureCoordinate2, and Texture2
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* DEF and USE constructs to share subtrees
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## Usage
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From an es6 module under Node (for example)
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```js
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import {convert} from 'vrml1to97'
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const vrml1spec = '# VRML 1.0 ....'
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const vrml97spec = convert(vrml1spec)
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```
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or from a script in a webpage
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```js
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(async () => {
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const vrml1to97 = await import('./dist/vrml1to97/index.js')
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const vrml1spec = '# VRML 1.0 ....'
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const vrml97spec = vrml1to97.convert(vrml1spec)
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})()
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```
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or from the command line via node
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```shell
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npx vrml1to97 < old.wrl > shinynew.wrl
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```
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## API
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Currently this package exports just two functions:
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* convert(vrml1: string, source?: string): string
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The main function, takes in VRML 1 syntax (note that it does not
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actually check that its input is VRML 1, so its behavior is undefined
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if given anything but valid VRML 1 syntax). Returns VRML 97 syntax for
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the same scene, as nearly as it can translate. Note that not all of
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VRML 1 is recognized (see above for a list of constructs that should
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be handled), and some of the translations may be somewhat approximate.
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If the optional second argument `source` is supplied, `convert` adds
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a comment indicating that the original vrml1 came from the specified
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source, before conversion to VRML97.
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* tree97(vrml1: string): Tree
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Takes the same input as convert, but rather than returning a string, it
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returns a very rough syntax tree for the converted VRML97 scene. The
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returned Tree data structure is an object whose keys are property names
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and whose values are lists of either strings or sub-Trees. Note however
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that this syntax tree does not represent a complete parse; since VRML 1
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and VRML97 are close, whole blocks of syntax are left as strings rather
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than broken into node names and property values. If there is a need to
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generate XML syntax output, for example, the code would need to be
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modified to break the tree down further to be ready for conversion to XML.
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## Conversion notes
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One sort of geometry common to VRML 1 and VRML97 is the IndexedFaceSet. These
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entities are often used to render solids. Indeed, the default in VRML97 is to
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assume they do represent a solid, with the normals pointing outward. Unusual
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visual effects ensue if the normals are not properly directed (basically, you
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see through the "front" of the solid and see the "backs" of the faces on the
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opposite side).
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As a result, unless the input VRML 1 explicitly includes an explicit
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vertexOrdering of CLOCKWISE or COUNTERCLOCKWISE, the default solid treatment
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will be turned off in the VRML97 output, meaning that all faces will be
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rendered opaque in both directions.
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