main.c

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <math.h>
#include <stdint.h>

#include <time.h>
#include <sys/time.h>
#include <unistd.h>
#include <poll.h>

#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/XKBlib.h>

const static int note_c3 = 48;

struct notes_map {
	int last_press;
	unsigned char notes[128];
};

static struct notes_map make_notes_map(void){
	struct { int start_note; unsigned char key_codes[20]; } rows[] = {
		{ note_c3 - 1, { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 } },
		{ note_c3 - 0, { 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 51 } },
		{ note_c3 + 1, { 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 36 } },
		{ note_c3 + 2, { 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 99 } }
	};

	struct notes_map m = {0};
	for (int y = 0; y < sizeof rows/sizeof *rows; y++){
		for (int x = 0; x < sizeof rows[y].key_codes/sizeof *rows[y].key_codes; x++) {
			unsigned char note = rows[y].start_note + x*3;
			unsigned char key_code = rows[y].key_codes[x];
			if (key_code >= sizeof m.notes) {
				// it's almost a Mozart joke
				fprintf(stderr, "Too many keys!\n");
				exit(EXIT_FAILURE);
			}
			m.notes[key_code] = note;
		}
	}
	return m;
}

static void handle_key(struct notes_map *m, unsigned int keycode, int state) {
	if(state){
		// ignore repeat
		if(m->last_press == (int)keycode)
			return;
		m->last_press = keycode;
	}else
		m->last_press = -1;

	if(keycode >= sizeof m->notes)
		return;
	int note = m->notes[keycode];
	if(note == 0)
		return;
	printf("note%s 0 %i 127\n", state? "on" : "off", note);
	fflush(stdout);
}

int main(void){
	struct notes_map notes_map = make_notes_map();

	Display *dpy;
	Window rootwin, win;
	XEvent e;
	int scr;
	GC gc;

	int width = 800;
	int height = 600;

	if(!(dpy = XOpenDisplay(NULL))){
		perror("XOpenDisplay");
		return 1;
	}

	if(!XkbSetDetectableAutoRepeat(dpy, True, &(Bool){0})){
		perror("XkbSetDetectableAutoRepeat");
		return 1;
	}

	scr = DefaultScreen(dpy);
	rootwin = RootWindow(dpy, scr);
	win = XCreateSimpleWindow(dpy, rootwin, 0, 0, width, height, 1, BlackPixel(dpy, scr), BlackPixel(dpy, scr));

	XStoreName(dpy, win, "Fluid Keys");

	gc = XCreateGC(dpy, win, 0, NULL);
	XSetForeground(dpy, gc, WhitePixel(dpy, scr));

	XSetWMHints(dpy, win, &(XWMHints){ .input = True, .flags = InputHint });

	XSelectInput(dpy, win, KeyPressMask | KeyReleaseMask);
	XMapWindow(dpy, win);

	for(;;){
		XNextEvent(dpy, &e);
		switch(e.type){
			case KeyPress:
			case KeyRelease:
				//printf("key%s: %u\n", e.type == KeyPress? "down" : "up", e.xkey.keycode);
				handle_key(&notes_map, e.xkey.keycode, e.type == KeyPress);
				break;
			default:
				fprintf(stderr, "type: %i\n", e.type);
		}
	}

	XCloseDisplay(dpy);

	return 0;
}