occt-import-js

The emscripten interface for OpenCascade import functionalities. It runs entirely in the browser, and allows you to import brep, step and iges files and access the result in JSON format.

See it in action in Online 3D Viewer, or check this fiddle for a code example.

How to install?

You can get occt-import-js from npm:

npm install occt-import-js

How to use?

The library runs in the browser and as a node.js module as well.

You will need two files from the dist folder: occt-import-js.js and occt-import-js.wasm. The wasm file is loaded runtime by the js file. There are three public functions in the library:

• ReadBrepFile to import brep file.
• ReadStepFile to import step file.
• ReadIgesFile to import iges file.

All functions have two parameters:

• content: The file content as a Uint8Array object.
• params: Triangulation parameters as an object, can be null.
  • linearUnit: Defines the linear unit of the output. Possible values: millimeter, centimeter, meter, inch, foot. Default is millimeter. Has no effect on brep files.
  • linearDeflectionType: Defines what the linear deflection value means. Default is bounding_box_ratio. Possible values:
  • bounding_box_ratio: The linearDeflection value contains a ratio of the avarage bounding box.
  • absolute_value: The linearDeflection value contains an absolute value in the unit defined by linearUnit.
  • linearDeflection: The linear deflection value based on the value of the linearDeflectionType parameter.
  • angularDeflection: The angular deflection value.

You can find more information about deflection values here.

Use from the browser

First, include the occt-import-js.js file in your website.

<script type="text/javascript" src="https://github.com/kovacsv/occt-import-js/raw/main/occt-import-js.js"></script>

After that, download the model file, and pass them to occt-import-js.

occtimportjs ().then (async function (occt) {
    let fileUrl = '../test/testfiles/simple-basic-cube/cube.stp';
    let response = await fetch (fileUrl);
    let buffer = await response.arrayBuffer ();
    let fileBuffer = new Uint8Array (buffer);
    let result = occt.ReadStepFile (fileBuffer, null);
    console.log (result);
});

Use as a node.js module

You should require the occt-import-js module in your script.

let fs = require ('fs');
const occtimportjs = require ('occt-import-js')();

occtimportjs.then ((occt) => {
    let fileUrl = '../test/testfiles/simple-basic-cube/cube.stp';
    let fileContent = fs.readFileSync (fileUrl);
    let result = occt.ReadStepFile (fileContent, null);
    console.log (result);
});

Processing the result

The result of the import is a JSON object with the following structure.

• success (boolean): Tells if the import was successful.
• root (object): The root node of the hierarchy.
  • name (string): Name of the node.
  • meshes (array): Indices of the meshes in the meshes array for this node.
  • children (array): Array of child nodes for this node.
• meshes (array): Array of mesh objects. The geometry representation is compatible with three.js.
  • name (string): Name of the mesh.
  • color (array, optional): Array of r, g, and b values of the mesh color.
  • brep_faces (array): Array representing the faces of the source b-rep.
  • first (number): The first triangle index of the face.
  • last (number): The last triangle index of the face.
  • color (array): Array of r, g, and b values of the color or null.
  • attributes (object)
  • position (object)
    • array (array): Array of number triplets defining the vertex positions.
  • normal (object, optional)
    • array (array): Array of number triplets defining the normal vectors.
  • index (object):
  • array (array): Array of number triplets defining triangles by indices.

How to build on Windows?

A set of batch scripts are prepared for building on Windows.

1. Install Prerequisites

Install CMake (3.6 minimum version is needed). Make sure that the cmake executable is in the PATH.

2. Install Emscripten SDK

Run the Emscripten setup script.

tools\setup_emscripten_win.bat

3. Compile the WASM library

Run the release build script.

tools\build_wasm_win_release.bat

4. Build the native project (optional)

If you want to debug the code, it's useful to build a native project. To do that, just use cmake to generate the project of your choice.

How to run locally?

To run the demo and the examples locally, you have to start a web server. Run npm install from the root directory, run npm start and visit http://localhost:8080.