From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: midi sound detecting in Allegro??
Date: Mon, 10 Mar 1997 10:11:31 +0000
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Distribution: world
Message-ID: <jTh7zbAT59IzEwAm@talula.demon.co.uk>
References: <yATjZAAJO4IzEwya AT jenkinsdavid DOT demon DOT co DOT uk>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

David Jenkins writes:
>Is it possible to detect when a certain sound is played in a midi file??
>
>I want to have the music in my demo affect something on the screen.
>Like make the background flash whever the drum is hit.

This can't be done with the standard API, but it's a simple modification
to the MIDI player. Edit midi.c, go to line 387 (the start of the
midi_note_on() function), and do whatever you have to...

Beware, though: some MIDI files use note-on messages with a volume of
zero to turn notes off (argh! why, when there's a different note-off
message?), so you should check for zero volumes.

Alternatively you could write a custom MIDI driver, which calls the
normal driver to play the sounds but also does special things in
response to note on messages. Eg. after install_sound(), write:

        MIDI_DRIVER *old_driver = midi_driver;
        midi_driver = &mydriver;

where mydriver is a MIDI_DRIVER structure you've filled in with all the
appropriate functions, along the lines of:

void my_key_on(int voice, inst, note, bend, vol, pan)
{
    old_driver->key_on(voice, inst, note, bend, vol, pan);
    // do cool stuff here
}


/*
 *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
 *  Beauty is a French phonetic corruption of a short cloth neck ornament.
 */