framebuffer

#include "nif.h"

static const int FD_CLOSED = -1;
ErlNifResourceType* FD_RES_TYPE = NULL;

static FrameBuffer* alloc_fd(ErlNifEnv* env, int fd, char *fbp, char *bbp, unsigned int screensize) {
  FrameBuffer* fbfd = enif_alloc_resource(FD_RES_TYPE, sizeof(FrameBuffer));
  fbfd->fd = fd;
  fbfd->fbp = fbp;
  fbfd->bbp = bbp;
  fbfd->screensize = screensize;
  return fbfd;
}

static void fb_destructor(ErlNifEnv* env, void* res) {
  DEBUG("closing framebuffer.");
  FrameBuffer* fbfd = (FrameBuffer*) res;
  if (fbfd->fbp != 0) munmap(fbfd->fbp, fbfd->screensize);
  close(fbfd->fd);
}

static int enif_get_framebuffer(ErlNifEnv* env, ERL_NIF_TERM framebuffer, FrameBuffer** fbfd) {
  ERL_NIF_TERM ref;
  FrameBuffer* fb;
  if (!enif_get_map_value(env, framebuffer, enif_make_atom(env, "ref"), &ref)) return 0;
  if (!enif_get_resource(env, ref, FD_RES_TYPE, (void **) &fb)) return 0;
  *fbfd = fb;

  return 1;
}

//
// API
//

static ERL_NIF_TERM open_framebuffer(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) {
  struct fb_var_screeninfo vinfo;
  struct fb_fix_screeninfo finfo;

  char *fbp, *bbp, *path;
  int fb = 0;
  unsigned int screensize = 0;
  ERL_NIF_TERM fd;
  FrameBuffer *fbfd = NULL;

  //***** Parse args.
  if (argc != 1) goto badarg;

  ErlNifBinary device;
  if (!enif_inspect_iolist_as_binary(env, argv[0], &device)) goto badarg;
  path = strndup((char*) device.data, device.size);
  enif_release_binary(&device);

  //***** Open the file descriptor to /dev/fb0.
  fb = open(path, O_RDWR);
  if (fb == FD_CLOSED) {
    free(path);
    goto err;
  }

  //***** Read fixed and variable framebuffer info.
  if (ioctl(fb, FBIOGET_FSCREENINFO, &finfo)) goto err;
  if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo)) goto err;
  screensize = vinfo.yres_virtual * finfo.line_length;

  //***** Open r/w pointers to memory representing the display.
  fbp = (char*)mmap(0, screensize * 2, PROT_READ | PROT_WRITE, MAP_SHARED, fb, (off_t)0);
  // Hard-coded to 32bit arch; warns on 64bit
  if ((int)fbp == -1) goto err;
  bbp = fbp + screensize;

  //***** Make the ref which can be passed back into the NIF.
  fbfd = alloc_fd(env, fb, fbp, bbp, screensize);
  fd = enif_make_resource(env, fbfd);
  enif_release_resource(fbfd);

  ERL_NIF_TERM framebuffer;
  if (!enif_make_framebuffer(env, finfo, vinfo, fd, &framebuffer)) return error_tuple(env, "Unable to create Framebuffer");

  return ok(env, framebuffer);

badarg:
  return enif_make_badarg(env);

err:
  /* if (screensize > 0 && fbp != 0) munmap(fbp, screensize * 2); */
  return error_tuple(env, strerror(errno));
}

static ERL_NIF_TERM info_framebuffer(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) {
  struct fb_var_screeninfo vinfo;
  struct fb_fix_screeninfo finfo;
  FrameBuffer* fbfd;
  ERL_NIF_TERM framebuffer;

  // PARSE ARGS
  if (argc != 1) goto badarg;
  framebuffer = argv[0];
  if (!enif_is_map(env, framebuffer)) goto badarg;
  if (!enif_get_framebuffer(env, framebuffer, &fbfd)) goto badarg;

  if (ioctl(fbfd->fd, FBIOGET_FSCREENINFO, &finfo)) goto err;
  if (ioctl(fbfd->fd, FBIOGET_VSCREENINFO, &vinfo)) goto err;

  if (!fb_put_finfo(env, finfo, &framebuffer)) return error_tuple(env, "Unable to set finfo");
  if (!fb_put_vinfo(env, vinfo, &framebuffer)) return error_tuple(env, "Unable to set vinfo");

  return ok(env, framebuffer);

badarg:
  return enif_make_badarg(env);

err:
  return error_tuple(env, strerror(errno));
}

static ERL_NIF_TERM put_pixel(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) {
  struct fb_var_screeninfo vinfo;
  struct fb_fix_screeninfo finfo;
  FrameBuffer* fbfd;
  unsigned int x = 0,
               y = 0,
               pixel_offset = 0;

  int color_arity;
  const ERL_NIF_TERM *color;
  int red, green, blue;

  // PARSE ARGS
  if (argc != 4) goto badarg;
  if (!enif_is_map(env, argv[0])) goto badarg;
  if (!enif_get_framebuffer(env, argv[0], &fbfd)) return error_tuple(env, "Error reading ref from Framebuffer");
  if (!enif_get_uint(env, argv[1], &x)) return error_tuple(env, "x must be an unsigned int");
  if (!enif_get_uint(env, argv[2], &y)) return error_tuple(env, "y must be an unsigned int");
  // color
  if (!enif_get_tuple(env, argv[3], &color_arity, &color)) return error_tuple(env, "Color should be a tuple in the format {red, blue, green}");
  if (color_arity != 3) return error_tuple(env, "Color should be a tuple in the format {red, blue, green}");
  if (!enif_get_int(env, color[0], &red)) return error_tuple(env, "Color should be a tuple in the format {red, blue, green}");
  if (!enif_get_int(env, color[1], &green)) return error_tuple(env, "Color should be a tuple in the format {red, blue, green}");
  if (!enif_get_int(env, color[2], &blue)) return error_tuple(env, "Color should be a tuple in the format {red, blue, green}");

  // SCREENINFO
  if (ioctl(fbfd->fd, FBIOGET_FSCREENINFO, &finfo)) goto err;
  if (ioctl(fbfd->fd, FBIOGET_VSCREENINFO, &vinfo)) goto err;

  if (x > vinfo.xres) return error_tuple(env, "Pixel out of bounds");
  if (y > vinfo.yres) return error_tuple(env, "Pixel out of bounds");
  pixel_offset = (x + vinfo.xoffset) * (vinfo.bits_per_pixel / 8) + (y + vinfo.yoffset) * finfo.line_length;

  // WRITE PIXEL
  // If red has 5 bits, then values from 0-255 are converted to 0-31.
  // If green has 6 bits, then values from 0-255 are converted to 0-63.
  DEBUG("offset: %d, red: %d, green: %d, blue: %d", pixel_offset, red, green, blue);
  red = (red / (1 << (8 - vinfo.red.length)));
  green = (green / (1 << (8 - vinfo.green.length)));
  blue = (blue / (1 << (8 - vinfo.blue.length)));

  unsigned int c = (red << vinfo.red.offset) \
                     + (green << vinfo.green.offset) \
                     + (blue << vinfo.blue.offset);

  // Hard-coded to 16bit on 32bit arch
  *((unsigned short*)(fbfd->fbp + pixel_offset)) = c;

  DEBUG("normalized: red: %d, green: %d, blue: %d, color: %d", red, green, blue, c);

  return ATOM_OK(env);
badarg:
  return enif_make_badarg(env);

err:
  return error_tuple(env, strerror(errno));
}

//
// NIF
//

static int on_load(ErlNifEnv *env, void **priv, ERL_NIF_TERM load_info) {
  (void)(env);
  (void)(priv);
  (void)(load_info);

  ErlNifResourceType* rt = enif_open_resource_type(env,
      NULL, "framebuffer", fb_destructor, ERL_NIF_RT_CREATE, NULL);
  if (rt == NULL) return -1;

  assert(FD_RES_TYPE == NULL);
  FD_RES_TYPE = rt;

  return 0;
}

static ErlNifFunc exports[]= {
  { "open", 1, open_framebuffer, 0 },
  { "info", 1, info_framebuffer, 0 },
  { "put_pixel", 4, put_pixel, 0 }
};

ERL_NIF_INIT(Elixir.Framebuffer.NIF, exports, &on_load, NULL, NULL, NULL)