fmod-oxide

Safe rust bindings to the FMOD sound engine. This crate tries to be as rusty and low-cost as possible, without comprimising on any APIs. Certain APIs, such as loading banks from a pointer, are marked as unsafe, but are still available for use.

Currently in BETA.

I'm currently developing this crate in tandem with another game, which means most of the real world testing of this crate comes from one source and only on a Windows/Linux system. This means that for some functions/use cases I haven't gotten the API down quite yet. (Custom Filesystems, Mix Matrices, Mac Support, etc) Almost all of the crate is feature complete though. I need to fix some issues with API documentation, add support for more FMOD versions, and double check the safety of everything before I'm confident releasing this as anything but a beta.

Docs

Most documentation is copied directly from the FMOD docs, however some information (such as parameter values) are excluded. Please refer to the FMOD documentation for more usage information.

Memory management & Copy types

All FMOD objects are Copy, Clone, Send and Sync because it's possible to have multiple references to the same object. (e.g. loading a bank and then retrieving it by its path) There are a lot of use-cases where you may want to fetch something (like a bank) and never use it again. Implementing Drop to automatically release things would go against that particular use-case, so this crate opts to have manual release() methods instead.

This crate does not currently guard against use-after-frees, although it's something I have planned.

String types

fmod-oxide aims to be as zero-cost as possible, and as such, it uses UTF-8 C strings from the lanyard crate as its string type. This means that all FMOD functions take a &Utf8CStr instead of a &str or &CStr. &Utf8CStr is pretty cheap to construct (and can even be done statically with the c! macro), so this should not be a problem.

When FMOD returns a string, it will always return a Utf8CString (the owned version of Utf8CStr) because it's difficult to encode lifetime requirements of FMOD strings.

This applies to structs like fmod::studio::AdvancedSettings which store C strings. Converting structs like AdvancedSettings to their FFI equivalents is done by reference as to not pass ownership of the string to FMOD. FMOD seems to copy strings into its own memory, so this is ok?

When converting from an FFI struct to something like AdvancedSettings, the C string pointer is copied into a Utf8CString. This is unsafe as there are no guarantees that the pointer is valid or that the string is null-terminated and UTF-8. Luckily all FMOD functions return UTF-8 strings so this isn't really a problem in practice.

Undefined Behaviour and unsafe fns

I'm trying to make these bindings as safe as possible, if you find UB please report it! There are a couple cases related to thread safety (You can initialize FMOD to be thread unsafe) and panics that I am aware of and actively trying to fix.

Right now there are a some fns marked as unsafe that I'm not sure how to get working safely. System creation, initialization, and cleanup is a pretty big one- creating a system is really unsafe, and certain functions can only be called before or after system creation. Releasing a system is probably the most unsafe operation of all though, as it invalidates all FMOD handles associated with that system

Userdata

Userdata is really, really, really hard to make safe bindings for, because any libary that wants to will need to clean up userdata whenever the FMOD object it is attached to is released. Unfortunately, there's quite a lot of cases where it's not possible to do that. EventDescription and EventInstance is a pretty good example- you can set a callback when events are released to clean up their userdata. You can also set up a callback when banks are unloaded as well to also clean up their userdata. That callback would be a perfect place to clean up userdata on EventDescription however you can't access the EventDescriptions of a bank when that callback is fired.

Pretty much the only option here would be to either a) require the user to manually release userdata or b) leak memory. Neither of these are good.

Right now this crate stores userdata in a global slotmap alongside its owner, and every so often will remove userdata with invalid owners. This solution works best with a mark and sweep GC, which Rust does not have. We could somewhat solve this issue by doing this check in System::update. That would make System::update expensive- it would have an additional O(n) complexity added to it, which goes against the purpose of this crate.

It's difficult to associate userdata with an individual system in this system though- so we have to clear the slotmap whenever any system is released. Releasing a system is performed at the end of execution generally so this probably won't be an issue. The only other workaround would be to set the userdata pointer of any object returned to a hashmap that each system owns.

I'm still thinking on how to solve this issue, but I'll probably put this behind a feature gate and provide *mut c_void setters and getters as well. Not the approach I would like, but oh well.

If there was an easy way to enforce that a T is pointer sized and needs no Drop (at compile time) then I could use the approach I was going for early on in this crate and just transmute the T to a *mut c_void. (See this commit.)

Differences to other crates

libfmod is similar to this crate, but its major difference is that it is automatically generated from the FMOD documentation instead of using handwritten bindings like this crate. Because it's automatically generated, it has a much faster release schedule than this crate will, but the API is closer to the C API.

rust-fmod is outdated, has no studio bindings, and has major safety holes (userdata takes an &'a mut T and does no type checking, System creation functions are not marked as unsafe, etc)

fmod-rs I'll be honest, I wasn't aware of this crate until recently. It's missing studio bindings and is designed to be used with bevy. There's a couple decisions (like a reference counted Handle type) that are interesting but aren't zero cost. If my crate doesn't work for you, it's definitely worth checking out!