Displays waveform of default input device using SDL

wv-viewer.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>

#include <SDL.h>

struct draw_context
{
  float window[1024];
  SDL_FPoint points[1024];

  SDL_AudioDeviceID dev;
};

static void capture_callback (void* userdata, unsigned char* samples, int num_bytes)
{
  struct draw_context *c = userdata;

  int N = num_bytes / sizeof(float);
  int win_off = 1024 - N;

  memmove (c->window, c->window + N, win_off * sizeof(float));
  memcpy (c->window + win_off, samples, num_bytes);
}

static inline void draw (SDL_Renderer *r, struct draw_context *c)
{
  SDL_FPoint point;
  
  int i;
  float x = 0;
  
  SDL_SetRenderDrawColor(r, 0, 0, 0, 0xFF);
  SDL_RenderClear (r);

  SDL_LockAudioDevice (c->dev);
  
  for (i = 0; i < 1024; ++i)
  {
    point.x = x;
    point.y = (0.5 * c->window[i] + 0.5) * 720;
    
    c->points[i] = point;
    
    x += 1.25f;
  }

  SDL_UnlockAudioDevice (c->dev);
  
  SDL_SetRenderDrawColor(r, 0xFF, 0xFF, 0xFF, 0xFF);
  SDL_RenderDrawLinesF (r, c->points, 1024);
  SDL_RenderPresent (r);
}

int main(int argc, char ** argv)
{
  SDL_Init (SDL_INIT_AUDIO | SDL_INIT_VIDEO);
  
  SDL_Window *win = NULL;
  SDL_Renderer *r = NULL;
  SDL_Event evt;
  
  SDL_AudioDeviceID dev;
  SDL_AudioSpec want, have;

  struct draw_context *ctx;

  ctx = calloc (sizeof (struct draw_context), 1);
  if (!ctx)
  {
    fputs ("Failed allocating `struct draw_context'", stderr);
    
    goto end;
  }
    
  int running = 1;

  want.samples = 800;
  want.freq = 48000;
  want.format = AUDIO_F32;
  want.channels = 1;
  want.callback = capture_callback;
  want.userdata = ctx;

  dev = SDL_OpenAudioDevice (NULL, 1, &want, &have, 0);
  
  if (!dev)
  {
    fprintf (stderr, "SDL_OpenAudioDevice(): %s\n", SDL_GetError ());
    
    goto end;
  }
  
  win = SDL_CreateWindow (argv[0],
    SDL_WINDOWPOS_UNDEFINED,
    SDL_WINDOWPOS_UNDEFINED,
    1280, 720, 0);

  if (!win)
  {
    fprintf (stderr, "SDL_CreateWindow(): %s\n", SDL_GetError ());
    
    goto end;
  }

  r = SDL_CreateRenderer (win, -1,
    SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);

  if (!r)
  {
    fprintf (stderr, "SDL_CreateRenderer(): %s\n", SDL_GetError());

    goto end;  
  }

  SDL_PauseAudioDevice (dev, 0);

  while (running)
  {
    while (SDL_PollEvent (&evt))
      switch (evt.type)
      {
        case SDL_QUIT:
          running = 0;
        break;
        
        case SDL_KEYDOWN:
          switch (evt.key.keysym.sym)
          {
            case SDLK_ESCAPE:
              running = 0;
            break;

            default:
            break;
          }
        break;
        
        default:
        break;
      }

    draw (r, ctx);
  }

  SDL_PauseAudioDevice (dev, 1);

end:
  if (r)
    SDL_DestroyRenderer (r);
  
  if (win)
    SDL_DestroyWindow (win);

  if (dev)
    SDL_CloseAudioDevice (dev);

  if (ctx)
    free (ctx);
  
  SDL_Quit ();
}