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
• 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.

Performances

Decompression timing and size for a few models tested on a somewhat dated pc. (Intel Core i5-3450 @ 3.10GHz). Jvascript decompression time drops dramatically for repeadted run of complex algorithms, hence the 10th run result.

Bunny mesh 34K vertices (12 bits precision) courtesy of Stanford

Bunny	Corto	Draco	OpenCTM
Size	62.8KB	63.6KB	168KB
C++ decode	2.3ms	25ms*	18ms*
Js first run	27ms	495ms	113ms
Js 10th run	6.5ms	30ms	52ms
Js lib size	26KB	673KB	17KB

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

Proserpina	Corto	Draco	OpenCTM
	982KB	779KB	1.13MB
C++ decode	23ms	220ms*	100ms*
Js first run	100ms	1120ms	420ms
JS 10th run	60ms	490ms	330ms

Palmyra point clout 500K vertices (18 bits), textures (12 bits) courtesy of robotgoat in Sketchfab

Palmyra	Corto	Draco
	282KB	301KB
C++ decode	28ms	644ms*
Js first run	110ms	2400ms
JS 10th run	65ms	1600ms

• C++ timing might be somewhat affected by compilation flags
• OpenCTM larger size is due mainly to simpler connectivity compression,
• Draco Javascript lib size is due to emscripten.

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>

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.