/* Simple dumb zoomable audio oscilloscope using ALSA alsa-utils.
 *
 * arecord sometimes craps out in the middle, especially when using
 * 48ksps and getting buffer overruns, so we restart it; also, I’ve
 * gotten lots of problems where it will fail at first because
 * something else still has the audio open.  The 60-millisecond buffer
 * (-B 60000) is a balance between the risk of getting buffer overruns
 * and the latency and jitter imposed by a large buffer, which for
 * some reason defaults to 500ms.
 *
 * There is no shortage of ways you could improve this
 * oscilloscope — brightness adjustment, overflow protection
 * (saturating arithmetic, plus maybe a bit of blur) for the beam
 * trace, a graticule, partial screen updates at wide zooms, support
 * for varying sample rates, interpolation between samples for
 * high-frequency signals, FFT display, triggering, waveform storage,
 * big-endian support, 96ksps support (though my sound card’s 96ksps
 * support is totally fake), etc.
 */
#define _BSD_SOURCE             /* for usleep */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include "xshmu.h"

int main()
{
  xshmu w = xshmu_open("oscope", 1536, 1080, "");
  char *cmd = "arecord -f S16_LE -r 48000 -B 60000";
  FILE *pipe = popen(cmd, "r");
  int ts = 1;                   /* timescale */

  for (;;) {
    for (xshmu_event *ev; (ev = xshmu_get_event(w));) {
      if (xshmu_as_die_event(ev)) return 0;
      xshmu_key_event *kev = xshmu_as_key_event(ev);
      if (kev && kev->down) {
        if (ts > 1 && kev->keysym == '+') ts /= 2;
        if (ts <= 8 && kev->keysym == '-') ts *= 2;
      }
    }

    xshmu_pic fb = xshmu_framebuffer(w);
    memset(fb.p, 0, fb.w*fb.h*4);
    int b = fb.h / 2,           /* Y-intercept, or offset */
      mi = (32768 + b - 1) / b; /* inverse slope, or gain */
    int16_t buf[65536];
    int n = fread((char*)&buf, 2, fb.w*ts, pipe);
    for (int i = 0; i < n; i++) *xshmu_pix(fb, i/ts, b+buf[i]/mi) += 0x337755;
    xshmu_flush(w);

    if (n == 0) {               /* restart arecord if it fails */
      pclose(pipe);
      usleep(100000);           /* but not without pausing */
      pipe = popen(cmd, "r");
    }
  }
}