Separate crate for FMOD plugins development

[lebedec]

based on #14

We probably need a separate crate without linking that will contain everything we need for FMOD DSP plugins development.

• Author of the original issue is correct that linking feels wrong via plugin development
• SDK contains separated fmod_dsp.h which noted as header for DSP plugins development
• We should be sure that plugins don't call FMOD functions and no need FMOD context

Probable solution:

A new crate libfmod-dsp-plugin based on fmod_dsp.h header which contains only definitions for DSP plugins development. Version and backward compatibility based on FMOD_PLUGIN_SDK_VERSION (provided by FMOD team). No linking. No FMOD context bindings.

Blocker:

Need more docs except white papers or any FMOD developer expertise to be sure that this solution correct

[lebedec]

There are 3 plugin types:

• Codec
• DSP
• Output

In application runtime they can be provided all the ways

In SDK each plugin has separate header with its own version FMOD_xxx_PLUGIN_VERSION:

• fmod_codec.h
• fmod_dsp.h
• fmod_output.h

All these definitions must be provided in common FMOD library (included in fmod_common.h which included in fmod.h)

Also, I think there is no much sense to provide Rust safe wrappers for plugin definitions because. Almost all definitions of plugin is callbacks with C FFI interfaces. Maybe we need separate libfmod-sys crate (this is also recommended by the Rust FFI guidelines).

Draft, new libfmod crates hierarchy:

[melody-rs]

Feel free to use fmod-audio-sys!

[lebedec]

About wrappers for plugin API.

There are issues for short period of time. All occured becuase of "safe" conversion:

• Getting DSP info/data leads to unaligned tcache chunk crash on Linux #20
• Potential STATUS_HEAP_CORRUPTION from dsp.get_info() implementation #19
• Segfault when adding more than one parameter to a custom DSP #18

Also, working with plugin API in any case leads to raw FFI: specific pointers defintion, byte buffers, C unions, C callbacks, etc

I am becoming more and more confident that FMOD plugins API structures like FMOD_DSP_DESCRIPTION must be raw FFI without wrappers.