Corto is a library for compression and decompression meshes and point clouds (C++ and Javascript).

Demo

Features

Corto compression library supports point clouds and meshes with per vertex attributes: normals, colors, texture coordinates and custom attributes.

The main focus of this work is on decompression speed, see performances, both for C++ lib and javascript, while still provide acceptable compression rates.

• corto is program to compress .ply and .obj models
• libcorto is a C++ compression/decompression library
• corto.js a javascript library for .crt decompression
• corto.em.js an emscripten library for .crt decompression (NEW! faster)
• CORTOLoader, a threejs loader

This work is based on the compression algorithm developed for the Nexus project for creation and visualization of multiresolution models. See Fast decompression for web-based view-dependent 3D rendering.

Entropy compression is based on Tunstall coding, decompression require only table lookup and is very fast while similar in compression ratio to Huffman where the number of symbols is small.

The C++ code is released under GPL licence, the Javascript code under MIT licence.

Performances

Decompression timing and size for a few models tested on a midlevel notebook. (Intel® Core™ i7-8550U CPU @ 1.80GHz × 8 ). Things changed from the last time I made some timings: emscripten (and draco) improved a lot, corto is now available in emscritpem too.

Draco library has a compression level settings from 1 (lower compression, faster) to 10 (higher compression, slower decompression) with 7 being the default.

Bunny mesh 34K vertices (14 bits precision) courtesy of Stanford

Bunny	Corto	Draco cl 1	Draco cl 7
Size	95.8KB	122.0KB	82.3KBH
C++ decode	2ms	7ms	9ms
Js Chrome	4.6ms	10ms	13ms
Js Firefox	8ms	12ms	18ms
Js lib size (gz)	28KB	268KB	268KB

Proserpina mesh 128K vertices (14 bits), textures (12 bits), normals (10 bits) courtesy of egiptologo91 in Sketchfab

Proserpina	Corto	Draco cl 1	Draco cl 7
	872KB	1080KB	672MB
C++ decode	18ms	62ms*	170ms*
Js Chrome	31ms	62ms	280ms
JS Firefox	41ms	88ms	280ms

The Nile - Vatican Museums point cloud 167K vertices (14bits), textures (12 bits), normals(10 bits) courtesy of egiptologo91 in Sketchfab

Nile	Corto	Draco cl 1	Draco cl 7
	890KB	1.92MB	1.70MB
C++ decode	7ms	43ms	81ms
Js Chrome	18ms	104ms	118ms
JS Firefox	32ms	123ms	128ms

• C++ timing might be affected by compilation flags

Building

The program and the library have no dependencies, g++ on linux and VisualStudio on Windows have been tested, but it should work everywhere with slight modifications.

Using g++

make -f Makefile.linux

Using qt:

qmake corto.pro
make

Using cmake:

cmake ./
make

Tools

corto

This program creates the .crt compressed model.

Usage:

corto [options] file

FILE is the path to a .ply or a .obj 3D model.
	-o <output>: filename of the .crt compressed file.
	             if not specified the extension of the input file will be replaced.
	-e <key=value>: add an exif property, or more than one.
	-p : treat the input as a point cloud."
	-v <bits>: vertex bits quantization. If not specified an euristic is used
	-n <bits>: normal bits quantization. Default 10.
	-c <bits>: color bits quantization. Default 6.
	-u <bits>: texture coordinate bits. Default 10.
	-q <step>: quantization step unit (float) instead of bits for vertex coordinates
	-N <prediction>: normal prediction can be:
	                 delta: use difference from previous normal (fastest)
	                 estimated: use difference from compute normals (cheaper)
	                 border: store difference only for boundary vertices (cheapest)
	-P <file.ply>: decompress and save as .ply for debugging purpouses

Material groups for obj (newmtl) and ply with texnumbers are preserved into the crt model.

CORTOLoader

CORTOLoader.js is similar to THREE.OBJLoader in functionality, and can easily replace it in three.js.

var loader = new THREE.CORTOLoader({ path: path });  
//materials autocreated, pass option loadMaterial: false otherwise.

loader.load(model, function(mesh) {
	mesh.addEventListener("change", render);         //if textures could be needed for materials

	if(!mesh.geometry.attributes.normal)
		mesh.geometry.computeVertexNormals();

	scene.add(mesh); 
	render();
});

See demo.html for details.

corto_js

CortoDecoder decodes a .crt as an arraybuffer and returns an objects with attributes (positions, index, colors etc).

<script src="js/corto.js"/>
<script>
var request = new XMLHttpRequest();
request.open('GET', 'bun_zipper.crt');
request.responseType = 'arraybuffer';
request.onload = function() {
	var decoder = new CortoDecoder(this.response);
	var model = decoder.decode();
	console.log(model.nvert, model.nface, model.groups);
	console.log('Index: ', model.index);
	console.log('Positions: ', model.position);
	console.log('Colors: ', model.color);
	console.log('Nornmals: ', model.normal);
	console.log('Tex coords: ', model.uv);
	//custom attributes can be encoded, see cortolib below for details.
}
request.send();
</script>

corto_em

CortoDecoder decodes a .crt as an arraybuffer and returns an objects with attributes (positions, index, colors etc). The interface is slightly different. No decode object, just a decode function, with support for 16 bit indexes and normals.

<script src="js/corto.js"/>
<script>
var request = new XMLHttpRequest();
request.open('GET', 'bun_zipper.crt');
request.responseType = 'arraybuffer';
request.onload = function() {
	var shortIndex = false;
	var shortNormals = true;
	var model = CortoDecoder.decode(this.response, shortIndex, shortNormals);
	console.log(model.nvert, model.nface, model.groups);
	console.log('Index: ', model.index);
	console.log('Positions: ', model.position);
	console.log('Colors: ', model.color);
	console.log('Nornmals: ', model.normal);
	console.log('Tex coords: ', model.uv);
	//custom attributes can be encoded, see cortolib below for details.
}
request.send();
</script>

libcorto

Interface is not entirely stable, no mayor change is expected. See src/main.cpp for an extensive example.

std::vector<float> coords;
std::vector<uint32_t> index;
std::vector<float> uv;
std::vector<float> radius;

//fill data arrays...

crt::Encoder encoder(nvert, nface);

//add attributes to be encoded
encoder.addPositions(coords.data(), index.data(), vertex_quantization_step);
encoder.addUvs(uvs.data(), pow(2, -uv_bits));

//add custom attributes
encoder.addAttribute("radius", (char *)radiuses.data(), crt::VertexAttribute::FLOAT, 1, 1.0f);

const char *compressed_data = encoder.stream.data();
const uint32_t compressed_size = encoder.stream.size();

Decoding

crt::Decoder decoder(size, data);

//allocate memory if needed
coords.resize(decoder.nvert*3);
index.resize(decoder.nface*3);

//tell the decoder where to decompress data
decoder.setPositions(coords.data());

if(decoder.data.count("uv")) {
	out.uvs.resize(decoder.nvert*2);
	decoder.setUvs(out.uvs.data());
}
//actually decode
decoder.decode();

Tunstall

TODO.