openjpeg VS ui-mock

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

It's quite possible to develop Rust for Windows without using Windows.

Try my open source "ui-mock".[1] This is a test of the cross-platform stack. Just get the repository with "git clone", and make sure you have Rust installed for target "x86_64-pc-windows-gnu". See the Cargo.toml file for build instructions.

This is a game-type user interface. It's just some menus and a 3D cube. It doesn't do much, but it exercises all the lower levels. This allows debugging cross-platform problems in a simple environment. The main crates used are winit (cross-plaform window event handling), wgpu (cross-plaform GPU handling), rfd (cross-platform file dialogs), keychain (cross-platform password storage), egui (Rust-native menus and dialogs), and rend3 (safe interface to wgpu). For graphics, it uses Vulkan, so it will run on Windows back to the last release of Windows 7. Not Windows 95, though; it's 64-bit. It will also run under Wine, so you don't even need a Windows system to test.

My metaverse client uses the same stack. It's compiled on Linux, and runs on both Linux and Windows. So I'm building a high-performance 3D graphics program for Windows without even owning a Windows system or using any Microsoft software.

[1] https://github.com/John-Nagle/ui-mock

Profiling on the CPU side is well handled by tracy, which is a game-oriented profiler. My programs render-bench and ui-mock are prepped for Tracy, as is Rend3, so you can try it out on them.

ui-mock -- game GUI test fixture This exercises rfd->egui->rend3->wgpu. It's a game GUI with menus and dialogs, but no game behind it, just a 3D drawing of a cube. It's useful for making bugs in that stack repeatable. That's been helpful in wringing out obscure bugs in egui.

Egui works well with Rend3. Here's my example and library for that. It's a dummy game UI; no game, but brings up menus atop Rend3 3D. Egui is very low level. Each dialog takes a lot of code. Something to generate dialogs from some kind of template would be useful. I have many of those to do. Incidentally, does anyone have examples of good color themes for egui? The default is shades of black on black, which is a bit harsh. I'd like to see some examples where the aesthetics are better.

There's an attempt to make this work for Rust desktop applications. There's the winit crate, which does cross-platform windowing and event loops. There's egui, for menus and subwindows. There's rfd, for file dialogs, which are special for security reasons. And there's wgpu, for cross-platform 3D.

I'm using all of these in my ui-mock,[1] which is a GUI for a game without the game. It has 3D graphics with 2D GUI elements on top. I'm using this to shake down all the cross-platform problems for my metaverse client. My own code, which is 100% safe Rust, has no platform dependent code.

Results are pretty good. There's minor dirty laundry in those libraries, which has been reported to the various maintainers. Stuff like this:

- You can get a file dialog hidden behind the main window, which, in a full screen program, is a real problem. Mostly a Linux problem; works fine on Windows.

- Full screen on Windows mode under Wine 7 crashes Wine. Known Wine bug.

- Warnings from WGPU, but it works around all of them with some minor performance loss.

- Cross-platform packaging, to make a Windows installer without Windows, isn't implemented yet.

So, not big stuff. A lot of stuff works that you might not expect to work, such as profiling with tracy. Wgpu is taking care of Vulkan vs Apple's Metal. (Apple just had to Think Different, to the annoyance of everybody doing 3D.) Opening a web page in the default browser is cross-platform. You can cross-compile - I build the Windows version on Linux, without using any Microsoft tools.

With some more work, I could make this work on WASM and Android as well, but that requires some special casing, mostly because WASM doesn't have proper threads.

So cross-platform desktop development is working pretty well. Most of the problems I'm running into would not appear in a more typical application.

[1] https://github.com/John-Nagle/ui-mock

I have a Rend3/Egui/WGPU program, https://github.com/John-Nagle/ui-mock