Does al_set_new_display_adapter affect al_get_display

Does al_set_new_display_adapter affect al_get_display_mode?

Edgar Reynaldo

Major Reynaldo

May 2007

Like the title says, does al_set_new_display_adapter affect the results of al_get_display_mode? I want to know the available modes for each adapter there is. That way I can detect my HDTV resolution programmatically through the HDMI cable, as well as other monitors.

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Elias

Member #358

May 2000

Yes, look here: https://github.com/liballeg/allegro5/blob/master/src/win/d3d_disp.cpp#L2895

      int adapter = al_get_new_display_adapter();
      if (adapter < 0)
         adapter = 0;

      if (!_al_pixel_format_is_real(allegro_formats[j]) || _al_pixel_format_has_alpha(allegro_formats[j]))
         continue;

      num_modes = _al_d3d->GetAdapterModeCount(adapter, (D3DFORMAT)d3d_formats[j]);

So it does uses the current adapter when listing the available modes.

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Kris Asick

Member #1,424

July 2001

I'm going to say "yes", but that's just a guess. The simplest way to test would be to quickly write in some debug code which outputs the results of al_get_num_video_adapters() so you know how many adapters you can set to (in case the entirety of the desktop space counts as one), then simply set one of those adapters and report the result of al_get_num_display_modes() for each one. If the results differ for each video adapter, the answer to your question is yes. If not, the answer is no.

EDIT: Nevermind. Better answer posted above while I was writing this post.

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Edgar Reynaldo

Major Reynaldo

May 2007

Looks like _al_wgl_get_display_mode enumerates them every time, but it totally ignores the adapter entirely. So you can't rely on it with OpenGL.

I'm not sure where the comment in _al_wgl_get_num_display_modes is coming from, but you can get a list of the display devices on Windows by using EnumDisplayDevices. You don't have to create a window to do it either. So this function could easily be altered to use a specific adapter. EnumDisplayDevices returns a DEVMODE object with the number of bits per pixel, but it doesn't tell you the layout of the rgb structure.

OpenGL will use the adapter you set with al_set_new_display_adapter when you create a display, but right now there is now way to enumerate display modes on anything but the default display.

Unless I'm missing something, which I very well could be. :/

tls.c#SelectExpand
 285/* Function: al_set_new_display_adapter
 286 */
 287void al_set_new_display_adapter(int adapter)
 288{
 289   thread_local_state *tls;
 290
 291   if ((tls = tls_get()) == NULL)
 292      return;
 293
 294   if (adapter < 0) {
 295      tls->new_display_adapter = ALLEGRO_DEFAULT_DISPLAY_ADAPTER;
 296   }
 297   tls->new_display_adapter = adapter;
 298}

wgl_disp.c#SelectExpand
 1585
 1586int _al_wgl_get_num_display_modes(int format, int refresh_rate, int flags)
 1587{
 DEVMODE dm;
 int count = 0;
 1590
 /* FIXME: Ignoring format.
  * To get a list of pixel formats we have to create a window with a valid DC, which
  * would even require to change the video mode in fullscreen cases and we really
  * don't want to do that.
  */
 (void)format;
 (void)refresh_rate;
 (void)flags;
 1599
 memset(&dm, 0, sizeof(dm));
 dm.dmSize = sizeof(dm);
 1602
 while (EnumDisplaySettings(NULL, count, &dm) != false) {
    count++;
 }
 1606
 return count;
 1608}
 1609
 1610
 1611ALLEGRO_DISPLAY_MODE *_al_wgl_get_display_mode(int index, int format,
                                             int refresh_rate, int flags,
                                             ALLEGRO_DISPLAY_MODE *mode)
 1614{
 DEVMODE dm;
 1616
 /*
  * FIXME: see the comment in _al_wgl_get_num_display_modes
  */
 (void)format;
 (void)refresh_rate;
 (void)flags;
 1623
 memset(&dm, 0, sizeof(dm));
 dm.dmSize = sizeof(dm);
 1626
 if (!EnumDisplaySettings(NULL, index, &dm))
    return NULL;
 1629
 mode->width = dm.dmPelsWidth;
 mode->height = dm.dmPelsHeight;
 mode->refresh_rate = dm.dmDisplayFrequency;
 mode->format = format;
 switch (dm.dmBitsPerPel) {
    case 32:
       if (format == ALLEGRO_PIXEL_FORMAT_ANY)
          mode->format = ALLEGRO_PIXEL_FORMAT_ANY_32_WITH_ALPHA;
       else if (format == ALLEGRO_PIXEL_FORMAT_ANY_NO_ALPHA)
          mode->format = ALLEGRO_PIXEL_FORMAT_ANY_32_NO_ALPHA;
       break;
    case 24:
       mode->format = ALLEGRO_PIXEL_FORMAT_ANY_24_NO_ALPHA;
       break;
    case 16:
       if (format == ALLEGRO_PIXEL_FORMAT_ANY)
          mode->format = ALLEGRO_PIXEL_FORMAT_ANY_16_WITH_ALPHA;
       else if(format == ALLEGRO_PIXEL_FORMAT_ANY_NO_ALPHA)
          mode->format = ALLEGRO_PIXEL_FORMAT_ANY_16_NO_ALPHA;
       break;
    default:
       break;
 }
 1653
 return mode;
 1655}

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King Piccolo will make it so Then I could just flip it with some sweet, sweet matrix math.