Linux/ALSA Native MIDI backend #637
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This does not do anything yet, but does set up the necessary build changes so that we will link against the libasound library.
We don't write any MIDI data to the sequencer yet but this sets up the basic foundations. For now, the playback thread just exits immediately, so `playmus` completes successfully.
We try various different ports that are usually the "default"; we need to provide a mechanism to specify it explicitly but for now this will do. These are the same "default" ports that DOSbox's ALSA code tries.
This converts all the common MIDI events to the ALSA event types. The converted events are not yet sent to ALSA.
With this change in place the module actually works! There's more still to finish but this is actually usable.
The ALSA device we're sending messages to will continue playing them even if the program quits, and we don't want to leave notes hanging. So when stopping the current track, send the "notes all off" and "reset all controllers" messages to every channel, and also send an ALSA reset event as well for good measure (the Timidity++ daemon seems to respond to it)
When stopping a song we must wait for the playback thread to terminate. However, the thread may currently be doing a blocking write of some MIDI events and we don't actually know how long this may take to complete. Instead, we can use non-blocking mode and the poll() system call. This allows us to sleep when the output event buffer is full, but also allows us to wake it back up when it's time for the song to stop. We accomplish this by creating a pipe that we close on shutdown.
And I missed that this is agaignst SDL2 branch, which I believe that we want to leave alone? Adapting things from this one to SDL3_mixer (main branch) would be best, I guess? |
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Yes, this should go in SDL3, not SDL2. |
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I'm fine with us going with the #595 route instead. Just really happy to see SDL_mixer get a Linux midi backend at last! If there is anything from my implementation that look like it's missing from the one that got merged, please let me know and I can adapt it. |
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I don't immediately see anything missing. One thing I am unsure about is Sysex handling, as I don't think my implementation passes them through. I'll look into it shortly. |
Great, thanks |
I have a personal interest in making sure sysex messages are handled properly (one of my original motivations was to be able to hook up synths like the Roland sc55) so if you don't have the time to look into it please say and I can take it off your hands |
Please have a look at #679 and let me know if it works. |
This (finally!) adds a native MIDI backend for Linux using the ALSA sequencer interface. I've tested this with Chocolate Doom and the Timidity++ ALSA daemon and it works pretty reliably; I haven't gotten around to testing with actual hardware yet. There are still a couple of features missing but it should be complete enough now for people to start using it.