thirdroom VS openjpeg

Not sure if Mozilla Hubs federates, but as already said, ThirdRoom is Matrix VRchat thing.

you can calculate 2D CSS transforms which match the equivalent transforms of your WebGL scene in WebXR - as an efficient but hacky way to (for instance) do live video overlays in 3D without having to mess around importing the video texture into WebGL (assuming you don’t need occlusion or environmental effects etc).

we’re toying with this as an approach for video overlays in https://thirdroom.io, especially for underpowered devices.

by “matrix chat 3d like things” do you mean https://thirdroom.io?

It would be super easy to build something like this on Third Room - and then get e2ee and decentralisation etc for free :)

oh, wow. we have 3D Tile support in https://thirdroom.io but had only ever found NASA’s Mars dataset as a good set of tiles to point it at. This could effectively turn Third Room into a FOSS, decentralised, E2EE multiplayer Google Earth running over Matrix!

AT proto has some significant similarities to Matrix:

* Both are work by self-authenticating git-style replication of Merkle trees/DAGs

* Both define strict data schemas for extensible sets of events (Matrix uses JSON schema - https://github.com/matrix-org/matrix-spec/tree/main/data/eve... and OpenAPI; AT uses Lexicons)

* Both use HTTPS for client-server and server-server traffic by default.

* Both are focused on decentralised composable reputation - e.g. https://matrix.org/blog/2020/10/19/combating-abuse-in-matrix... on the Matrix side, or https://paulfrazee.medium.com/the-anti-parler-principles-for... on the bluesky side, etc.

* Both are designed as big-world communication networks. You don't have the server balkanisation that affects ActivityPub.

* Both eschew cryptocurrency systems and incentives.

There are some significant differences too:

* Matrix aspires to be the secure communication layer for the open web.

* AT aspires (i think) to be an open decentralised social networking protocol for the internet.

* AT has portable identity by default. We've been working on this on Matrix (e.g. MSC1228 - https://github.com/matrix-org/matrix-spec-proposals/pull/122... and MSC2787 - https://github.com/matrix-org/matrix-spec-proposals/blob/nei...) and have a new MSC (and implementation on Dendrite) in progress right now which combines the best bits of MSC1228 & MSC2787 into something concrete, at last. In fact the proto-MSC is due to emerge today.

* AT is proposing a asymmetrical federation architecture where user data is stored on Personal Data Servers (PDS), but indexing/fan-out/etc is done by Big Graph Servers (BGS). Matrix is symmetrical and by default federates full-mesh between all servers participating in a conversation, which on one hand is arguably better from a self-sovereignty and resilience perspective - but empirically has created headaches where an underpowered server joins some massive public chatroom and then melts. Matrix has improved this by steady optimisation of both protocol and implementation (i.e. adding lazy loading everywhere - e.g. https://matrix-org.github.io/synapse/latest/development/syna...), but formalising an asymmetrical architecture is an interesting different approach :)

* AT is (today) focused on for public conversations (e.g. prioritising big-world search and indexing etc), whereas Matrix focuses both on private and public communication - whether that's public chatrooms with 100K users over 10K servers, or private encrypted group conversations. For instance, one of Matrix's big novelties is decentralised access control without finality (https://matrix.org/blog/2020/06/16/matrix-decomposition-an-i...) in order to enforce access control for private conversations.

* Matrix also provides end-to-end encryption for private conversations by default, today via Double Ratchet (Olm/Megolm) and in the nearish future MLS (https://arewemlsyet.com). We're also starting to work on post quantum crypto.

* Matrix is obviously ~7 years older, and has many more use cases fleshed out - whether that's native VoIP/Video a la Element Call (https://element.io/blog/introducing-native-matrix-voip-with-...) or virtual worlds like Third Room (https://thirdroom.io) or shared whiteboarding (https://github.com/toger5/TheBoard) etc.

* AT's lexicon approach looks to be a more modular to extend the protocol than Matrix's extensible event schemas - in that AT lexicons include both RPC definitions as well as the schemas for the underlying datatypes, whereas in Matrix the OpenAPI evolves separately to the message schemas.

* AT uses IPLD; Matrix uses Canonical JSON (for now)

* Matrix is perhaps more sophisticated on auth, in that we're switching to OpenID Connect for all authentication (and so get things like passkeys and MFA for free): https://areweoidcyet.com

* Matrix has an open governance model with >50% of spec proposals coming from the wider community these days: https://spec.matrix.org/proposals

* AT has done a much better job of getting mainstream uptake so far, perhaps thanks to building a flagship app from day one (before even finishing or opening up the protocol) - whereas Element coming relatively late to the picture has meant that Element development has been constantly slowed by dealing with existing protocol considerations (and even then we've had constant complaints about Element being too influential in driving Matrix development).

* AT backs up all your personal data on your client (space allowing), to aid portability, whereas Matrix is typically thin-client.

* Architecturally, Matrix is increasingly experimenting with a hybrid P2P model (https://arewep2pyet.com) as our long-term solution - which effectively would end up with all your data being synced to your client. I'd assume bluesky is consciously avoiding P2P having been overextended on previous adventures with DAT/hypercore: https://github.com/beakerbrowser/beaker/blob/master/archive-.... Whereas we're playing the long game to slowly converge on P2P, even if that means building our own overlay networks etc: https://github.com/matrix-org/pinecone

I'm sure there are a bunch of other differences, but these are the ones which pop to the top of my head, plus I'm far from an expert in AT protocol.

It's worth noting that in the early days of bluesky, the Matrix team built out Cerulean (https://matrix.org/blog/2020/12/18/introducing-cerulean) as a demonstration to the bluesky team of how you could build big-world microblogging on top of Matrix, and that Matrix is not just for chat. We demoed it to Jack and Parag, but they opted to fund something entirely new in the form of AT proto. I'm guessing that the factors that went into this were: a) wanting to be able to optimise the architecture purely for social networking (although it's ironic that ATproto has ended up pretty generic too, similar to Matrix), b) wanting to be able to control the strategy and not have to follow Matrix's open governance model, c) wanting to create something new :)

From the Matrix side; we keep in touch with the bluesky team and wish them the best, and it's super depressing to see folks from ActivityPub and Nostr throwing their toys in this manner. It reminds me of the unpleasant behaviour we see from certain XMPP folks who resent the existence of Matrix (e.g. https://news.ycombinator.com/item?id=35874291). The reality is that the 'enemy' here, if anyone, are the centralised communication/social platforms - not other decentralisation projects. And even the centralised platforms have the option of seeing the light and becoming decentralised one day if we play our parts well.

What would be really cool, from my perspective, would be if Matrix ended up being able to help out with the private communication use cases for AT proto - as we obviously have a tonne of prior art now for efficient & audited E2EE private comms and decentralised access control. Moreover, I /think/ the lexicon approach in AT proto could let Matrix itself be expressed as an AT proto lexicon - providing interop with existing Matrix rooms (at least semantically), and supporting existing Matrix clients/SDKs, while using AT proto's ID model and storing data in PDSes etc. Coincidentally, this matches work we've been doing on the Matrix side as part of the MIMI IETF working group to figure out how to layer Matrix on top of other existing protocols: e.g. https://datatracker.ietf.org/doc/draft-ralston-mimi-matrix-t... and https://datatracker.ietf.org/doc/draft-ralston-mimi-matrix-m... - and if I had infinite time right now I'd certainly be trying to map Matrix's CS & SS APIs onto an AT proto lexicon to see what it looks like.

TL;DR: I think AT proto is cool, and I wish that open projects saw each other as fellow travellers rather than competitors.

You could take a look to this project: https://github.com/matrix-org/thirdroom As part of the project they are implementing a web Game engine, uses ThreeJS for graphics, and includes multiplayer using the Matrix protocol. Could be a good starting point.

Have you looked into what thirdroom or ambient have done in the space?

Have you lot made any friends over at Third Room yet? ;)

If you wanted to be serious about it, you could try to make something based on https://thirdroom.io

mkdir ~/install cd ~/install wget https://github.com/uclouvain/openjpeg/archive/master.zip unzip master.zip cd openjpeg-master/ mkdir build cd build cmake -DCMAKE_BUILD_TYPE=Release .. make sudo make install sudo make clean cd

Details here, if you like reading bug reports. It took the cooperation of developers at all four levels to fix this. I wrote a test project to reproduce the problem, the jpeg2k developer was able to reproduce the problem under valgrind (a tool for finding bad pointer references in C, seldom needed by Rust users), an OpenJPEG developer fixed the C code, and everybody in the chain updated versions. Thanks to everyone who had a part in this.

> The whole file is effectively a write-what-where primitive2. In addition to that, the Count Info Table is not bounds checked either...

File formats like that, with many offsets in the file, are troublesome. There used to be more formats like that. Microsoft Word .doc is the classic example.

OpenJPEG 2000 has a similar problem. I just hit that yesterday.[1] Valgrind is finding references to un-initialized data which affect control flow, and running the JPEG decoder on valid but truncated files (which is allowed) is causing bad memory reference crashes and errors.

New formats like this are rare. People have learned. A modern exception is Unreal Engine 5's Nanite has much offset data, and there may be an attack surface there for hostile game content. Nanite is a way to store a graphics mesh with both multiple levels of detail and common submeshes. It's a hierarchy of directed acyclic graphs, flattened into a linear file with offsets. And, sure enough, there are many crash reports. At least Unreal provides a validator for the format.

(If only C/C++ had slices in the language. Most of the things for which pointer arithmetic is used can be done with slices. Slices really are pointer arithmetic, with sanity.)

[1] https://github.com/uclouvain/openjpeg/issues/1459

JPEG 2000 decoder crashes Trying to read files at reduced resolution crashes with memory access errors. This is jpeg2k (Rust) calling jpeg2000-sys (Rust glue to C foreign function interfaces) calling OpenJPEG (all C). The problem can now be reproduced at the C level alone, under Valgrind. The developers of the top two levels have been very helpful, but the trouble is down in the rather painful C code at the bottom. The OpenJPEG maintainers are way behind on fixes, despite being funded.

It certainly was a risk in 2013, when the open source libraries were slow and riddled with bugs. Today, there are two stable, well maintained and fast open source libraries available:

https://github.com/uclouvain/openjpeg