A tweak to always force GZDoom onto a secondary display (useful for 3D monitors). See https://oldvcr.blogspot.com/2020/10/stereoscopic-computing-converting-quake.html

gzdoomdisplay.diff

--- sdlglvideo.cpp.OLD	2020-10-04 21:23:32.751041920 -0700
+++ sdlglvideo.cpp	2020-10-04 20:54:21.740470397 -0700
@@ -163,18 +163,19 @@
 			win_h = bounds.h * 8 / 10;
 		}
 
 		FString caption;
 		caption.Format(GAMENAME " %s (%s)", GetVersionString(), GetGitTime());
 
 		const uint32_t windowFlags = (win_maximized ? SDL_WINDOW_MAXIMIZED : 0) | SDL_WINDOW_RESIZABLE | extraFlags;
 		Priv::window = SDL_CreateWindow(caption,
-			(win_x <= 0) ? SDL_WINDOWPOS_CENTERED_DISPLAY(vid_adapter) : win_x,
-			(win_y <= 0) ? SDL_WINDOWPOS_CENTERED_DISPLAY(vid_adapter) : win_y,
+			//(win_x <= 0) ? SDL_WINDOWPOS_CENTERED_DISPLAY(vid_adapter) : win_x,
+			//(win_y <= 0) ? SDL_WINDOWPOS_CENTERED_DISPLAY(vid_adapter) : win_y,
+			SDL_WINDOWPOS_UNDEFINED_MASK | 1, SDL_WINDOWPOS_UNDEFINED_MASK | 1,
 			win_w, win_h, windowFlags);
 
 		if (Priv::window != nullptr)
 		{
 			// Enforce minimum size limit
 			SDL_SetWindowMinimumSize(Priv::window, VID_MIN_WIDTH, VID_MIN_HEIGHT);
 		}
 	}