js-openctm is a JavaScript library for reading OpenCTM files.

OpenCTM is a file format for storing 3D triangle meshes created by Marcus Geelnard.

Some parts of this library are a direct traslation to JavaScript from original C source code found on the OpenCTM SDK.

Demo

• Live demo!

• Using Three.js to render

Video

js-openctm

How to use it?

1) Retrieve your .ctm file from the web, as usual:

function retrieve(url){
  var request = new XMLHttpRequest();
  request.open("GET", url, false);
  request.overrideMimeType("text/plain; charset=x-user-defined");
  request.send();
  if ( (200 !== request.status) && (0 !== request.status) ){
    throw new Error(request.status + " Retrieving " + url); 
  }
  return request;
};

var request = retrieve("<your .ctm filename url here>");

2) Create a CTM.Stream object from the retrieved file:

var stream = new CTM.Stream(request.responseText);

3) Create a CTM.File object from the stream:

var file = new CTM.File(stream);

What do you get?

CTM.File objects have two properties:

• header, an object with the following properties:

  • fileFormat: File format version (always 5)
  • compressionMethod: Compression method (RAW, MG1 or MG2)
  • vertexCount: Vertex count
  • triangleCount: Triangle count
  • uvMapCount: UV map count
  • attrMapCount: Attribute map count
  • flags: Boolean flags (bit 0 means that normals are present)
  • comment: File comment

• body, an object with the following properties:

  • indices: A Uint32Array buffer with 3 x header.triangleCount elements
  • vertices: A Float32Array buffer with header.vertexCount elements
  • normals: (optional) A Float32Array buffer with header.vertexCount elements
  • uvMaps: (optional) An array with header.uvMapCount elements, each of them with the following properties:
    • name: UV map name
    • filename: UV map ?le name
    • uv: A Float32Array buffer with 2 x header.vertexCount elements
  • attrMaps: (optional) A array with header.attrMapCount elements, each of them with the following properties:
    • name: Attribute map name
    • attr: A Float32Array buffer with 4 x header.vertexCount elements

How to draw the mesh?

Using WebGL, of course.

...
indicesBuffer = gl.createBuffer();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indicesBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(file.body.indices), gl.STATIC_DRAW);

verticesBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, verticesBuffer);
gl.bufferData(gl.ARRAY_BUFFER, file.body.vertices, gl.STATIC_DRAW);

if (file.body.normals){
  normalsBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, normalsBuffer);
  gl.bufferData(gl.ARRAY_BUFFER,file.body.normals, gl.STATIC_DRAW);
}

if (file.body.uvMaps){
  uvBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, uvBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, file.body.uvMaps[0].uv, gl.STATIC_DRAW);
}
...

No idea? Try http://learningwebgl.com.

Dependencies

js-lzma: A port of the LZMA decompression algorithm to JavaScript.

Limitations

• Textures are not packed on .ctm files, you must retrieve them on your own.

• Indices are exposed like a Uint32Array buffer, but please, remember that WebGL drawElements function works with Uint16Array, you must split them on your own.

What about writer function?

Sorry, don't. This library is part of another project of mine that only needed the reader algorithm.