gl tf siggraph-2013

© Copyright Khronos Group 2013 | Page

Fabrice RobinetCOLLADA Working Group Chair.

graphics library Transmission Formathttps://github.com/KhronosGroup/glTF

Wednesday, July 24, 13

https://github.com/KhronosGroup/glTF

https://github.com/KhronosGroup/glTF


Overview

•status•motivations•design principles•glTF pipeline

•scope•glTF... and what more ?•demos



Status

•COLLADA Working group initiative.•Work in progress - Not a ratified specification yet.•Code work and SPEC work at the same time.•SPEC currently catching up with the converter.•Community feedback welcomed on GitHub.



Motivations

•Bridge the gap between 3D formats and GL based APIs.•Reduce duplicated effort in content pipeline.•A common format for contents providers.



Design principles

•Streamline rendering: size, speed and ease of implementation•Offload processing from runtime.•Maps well to GL APIs and Typed Arrays.•Neutral, specify higher level only when necessary.



glTF Pipeline - overview

OpenCOLLADA Compression

COLLADA2GLTF C++ Library

Rapidjson

COLLADA2GLTF command line tool

Rest3Dtransactions & access to 3D assets

COLLADA2GLTF DeliveryAuthor Interchange API

Maya

Blender

..

COLLADA glTF

OpenGL/ES

WebGL

OpenGL

Converter



glTF Pipeline - COLLADA2GLTF

• Triangulate

• Unify indices

• Split meshes

• Generate shaders• Axis up conversion

• Minify shaders

• Flatten hierarchy & combine meshes

• Convert images

• Compress meshes• Interleave vertices

• ... Suggestions welcomed !

Mandatory transformations

Planned optimizations & transformations



Scope

•1.0- Node hierarchy- Cameras- Lights- Key-framed animations- Skinning- Morphing- Medias (images & videos)

•mesh compression as extensions

•multi-pass considered.



Compression

•Tested 2 compression libraries:- Open3DGC: https://github.com/amd/rest3d/tree/master/server/

o3dgc- webgl-loader: https://code.google.com/p/webgl-loader/


https://github.com/amd/rest3d/tree/master/server/o3dgc




https://code.google.com/p/webgl-loader/

https://code.google.com/p/webgl-loader/


Open3DGC

•Open3DGC Binary is an implementation of the MPEG-SC3DMC (Scalable Compression 3D Mesh Compression)

•K. Mammou, T. Zaharia, F. Prêteux, “TFAN: A low complexity 3D mesh compression algorithm” Computer Animation and Virtual Worlds, Vol. 20(2-3), pp. 343–354, 2009

•2 modes: binary and ascii.- Open3DGC Binary exploits an adaptive arithmetic-based encoding to

exploit statistical properties of the encoded data- Open3DGC ASCII exploits a 7-bit ASCII encoding adapted for GZip

compression- Open3DGC ASCII is a slightly modified version of SC3DMC to

exploit GZip compression



ModelCOLLADACOLLADA glTFglTF glTF+Open3DGC

asciiglTF+Open3DGC

asciiglTF+Open3DGC

binaryglTF+Open3DGC

binaryModel

XML gzip raw gzip raw gzip raw •raw bin•gzip JSON

• bin:102k• JSON:11k

• bin:81k• JSON:2kb

• ascii:29k• JSON:11k




336k 106k 113k 83k 40k 21k 29k 20k• bin:9220k• JSON:75k




• bin: 1622k• JSON:151k

• bin: 1622k• JSON:11k

19767k 3417k 9295k 3225k 3231k 1521k 1773k 1633k

• bin:25224k• JSON:183k






56763k 7378k 25407k 5746k 8380k 1462k 3794k 3234k







794k 133k 584k 109k 389k 77k 338k 88k

NOT final numbers - will be refined with integration improvements.



Compression: results overview

data from rest3d SigGraph 2013 BOF presentation, Khaled Mammou/Remi Arnaud



Open3DGC compression

•First integration within “collada2gltf” available on GitHub.- naive integration to be improved (leading to better compression).

•Encoder/Decoder in C++•Just to get it working quickly, converted code using emscripten to javascript.

•Decoding performance to be evaluated in JS.



“webgl-loader” compression

• First integration within “collada2gltf” available on GitHub.- naive integration to be improved (leading to better compression).

• Encoder in C++/Decoder in JS

• Fast decoding.

Model COLLADACOLLADA glTF+webgl-loaderglTF+webgl-loader glTF+Open3DGC asciiglTF+Open3DGC ascii glTF+Open3DGC binaryglTF+Open3DGC binaryModelXML gzip raw gzip raw gzip raw •raw bin

•gzip JSON

• utf8:42k• JSON:12k

• utf8:34k•JSON:2kb





336k 106k 54k 36k 40k 21k 29k 20k•utf8:8747k• JSON:753k

•utf8:1325k• JSON:29k





56763k 7378k 9500k 1354k 8380k 1462k 3794k 3234k

NOT final numbers - will be refined with integration improvements.



Compression: next steps

•Fix integration issues: currently both Open3DGC and webgl-loader do not handle shared vertex buffer by multiple index buffers. Needed some vertex duplication to work-around this.

•Benchmark for decoding performance and memory footprint.

•Compress animations, bones indices and weight



glTF... and what more ?

•package not only “models” but whatever you need a declarative way•For instance, the viewer uses glTF “techniques” to:- draw the background gradient- setup the specific image based picking shaders



Demos

•Montage Model Viewer•MegaCity & Video demo•Skinning



Thank you - See you on GitHub !

Specification : https://github.com/KhronosGroup/glTF/blob/master/specification/README.mdconverter : https://github.com/KhronosGroup/glTF/convertermontagejs viewer : https://github.com/fabrobinet/glTF-webgl-viewer


https://github.com/KhronosGroup/glTF/blob/master/specification/README.md




https://github.com/fabrobinet/glTF-webgl-viewer

https://github.com/fabrobinet/glTF-webgl-viewer

gl tf siggraph-2013

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