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Does al_set_new_display_adapter affect al_get_display_mode?
Edgar Reynaldo
Member #8,592
May 2007
avatar

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.

--
"Either help out or stop whining" - Evert

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. ;)

--- Kris Asick (Gemini)
--- http://www.pixelships.com

Edgar Reynaldo
Member #8,592
May 2007
avatar

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{ 1588 DEVMODE dm; 1589 int count = 0; 1590 1591 /* FIXME: Ignoring format. 1592 * To get a list of pixel formats we have to create a window with a valid DC, which 1593 * would even require to change the video mode in fullscreen cases and we really 1594 * don't want to do that. 1595 */ 1596 (void)format; 1597 (void)refresh_rate; 1598 (void)flags; 1599 1600 memset(&dm, 0, sizeof(dm)); 1601 dm.dmSize = sizeof(dm); 1602 1603 while (EnumDisplaySettings(NULL, count, &dm) != false) { 1604 count++; 1605 } 1606 1607 return count; 1608} 1609 1610 1611ALLEGRO_DISPLAY_MODE *_al_wgl_get_display_mode(int index, int format, 1612 int refresh_rate, int flags, 1613 ALLEGRO_DISPLAY_MODE *mode) 1614{ 1615 DEVMODE dm; 1616 1617 /* 1618 * FIXME: see the comment in _al_wgl_get_num_display_modes 1619 */ 1620 (void)format; 1621 (void)refresh_rate; 1622 (void)flags; 1623 1624 memset(&dm, 0, sizeof(dm)); 1625 dm.dmSize = sizeof(dm); 1626 1627 if (!EnumDisplaySettings(NULL, index, &dm)) 1628 return NULL; 1629 1630 mode->width = dm.dmPelsWidth; 1631 mode->height = dm.dmPelsHeight; 1632 mode->refresh_rate = dm.dmDisplayFrequency; 1633 mode->format = format; 1634 switch (dm.dmBitsPerPel) { 1635 case 32: 1636 if (format == ALLEGRO_PIXEL_FORMAT_ANY) 1637 mode->format = ALLEGRO_PIXEL_FORMAT_ANY_32_WITH_ALPHA; 1638 else if (format == ALLEGRO_PIXEL_FORMAT_ANY_NO_ALPHA) 1639 mode->format = ALLEGRO_PIXEL_FORMAT_ANY_32_NO_ALPHA; 1640 break; 1641 case 24: 1642 mode->format = ALLEGRO_PIXEL_FORMAT_ANY_24_NO_ALPHA; 1643 break; 1644 case 16: 1645 if (format == ALLEGRO_PIXEL_FORMAT_ANY) 1646 mode->format = ALLEGRO_PIXEL_FORMAT_ANY_16_WITH_ALPHA; 1647 else if(format == ALLEGRO_PIXEL_FORMAT_ANY_NO_ALPHA) 1648 mode->format = ALLEGRO_PIXEL_FORMAT_ANY_16_NO_ALPHA; 1649 break; 1650 default: 1651 break; 1652 } 1653 1654 return mode; 1655}

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