From 509da82ee81585f9d8b53df930d4848cc4dc015b Mon Sep 17 00:00:00 2001
From: Dave Milici <milici.dave@gmail.com>
Date: Fri, 12 Mar 2021 10:07:45 -0800
Subject: [PATCH] Add -gl_stereoview option for selecting stereo viewport
 modes.

---
 common/include/args.h     |  1 +
 common/main/game.h        |  1 +
 similar/main/game.cpp     | 13 +++++++++----
 similar/main/gamecntl.cpp |  8 ++------
 similar/main/inferno.cpp  |  4 ++++
 similar/misc/args.cpp     |  2 ++
 6 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/common/include/args.h b/common/include/args.h
index 52ce2245f..b9668c3a4 100644
--- a/common/include/args.h
+++ b/common/include/args.h
@@ -102,6 +102,7 @@ struct CArg : prohibit_void_ptr<CArg>
 	bool DbgGlRGBA2Ok;
 	unsigned OglSyncWait;
 	bool OglStereo;
+	int  OglStereoView;
 #else
 	bool DbgSdlHWSurface;
 	bool DbgSdlASyncBlit;
diff --git a/common/main/game.h b/common/main/game.h
index 621a56b53..07b7f06d9 100644
--- a/common/main/game.h
+++ b/common/main/game.h
@@ -205,6 +205,7 @@ extern game_window *Game_wind;
 
 void game();
 void init_game();
+void init_stereo();
 void init_cockpit();
 extern void PALETTE_FLASH_ADD(int dr, int dg, int db);
 
diff --git a/similar/main/game.cpp b/similar/main/game.cpp
index 1ad75764d..3740ea6bf 100644
--- a/similar/main/game.cpp
+++ b/similar/main/game.cpp
@@ -193,10 +193,15 @@ namespace dsx {
 void init_stereo()
 {
 	// init stereo options
-	if (CGameArg.OglStereo) {
-		VR_stereo = true;
-//		VR_half_width = true;
-		VR_half_height = true;
+	if (CGameArg.OglStereo || CGameArg.OglStereoView) {
+		if (!VR_stereo && !VR_eye_offset)
+			VR_stereo = (CGameArg.OglStereoView) ? CGameArg.OglStereoView % 4 : true;
+		switch (VR_stereo) {
+			case 0: VR_half_width = VR_half_height = false; break;
+			case 1: VR_half_width = false; VR_half_height = true; break;
+			case 2: VR_half_width = true; VR_half_height = false; break;
+			case 3: VR_half_width = VR_half_height = true; break;
+		}
 		VR_eye_width = (F1_0 * 7) / 10;	// Descent 1.5 defaults
 		VR_eye_offset = (VR_half_width) ? -6 : -12;
 		PlayerCfg.CockpitMode[1] = CM_FULL_SCREEN;
diff --git a/similar/main/gamecntl.cpp b/similar/main/gamecntl.cpp
index 7f6bab7cb..0b3dbbe18 100644
--- a/similar/main/gamecntl.cpp
+++ b/similar/main/gamecntl.cpp
@@ -931,13 +931,9 @@ static window_event_result HandleSystemKey(int key)
 			break;
 		case KEY_SHIFTED + KEY_F8:
 		case KEY_SHIFTED + KEY_ALTED + KEY_F8:
-			if (CGameArg.OglStereo)
+			if (CGameArg.OglStereo || CGameArg.OglStereoView) {
 				++VR_stereo %= 4;
-			switch (VR_stereo) {
-				case 0: VR_half_width = VR_half_height = false; break;
-				case 1: VR_half_width = false; VR_half_height = true; break;
-				case 2: VR_half_width = true; VR_half_height = false; break;
-				case 3: VR_half_width = VR_half_height = true; break;
+				init_stereo();
 			}
 			break;
 
diff --git a/similar/main/inferno.cpp b/similar/main/inferno.cpp
index c873d80e9..c98e4bdfa 100644
--- a/similar/main/inferno.cpp
+++ b/similar/main/inferno.cpp
@@ -206,6 +206,10 @@ static void print_commandline_help()
 		VERB("  -gl_syncwait <n>              Wait interval (ms) for sync mode 2 (default: " DXX_STRINGIZE(OGL_SYNC_WAIT_DEFAULT) ")\n")	\
 		VERB("  -gl_darkedges                 Re-enable dark edges around filtered textures (as present in earlier versions of the engine)\n")	\
 		VERB("  -gl_stereo                    Enable OpenGL stereo quad buffering, if available\n")	\
+		VERB("  -gl_stereoview <n>            Select OpenGL stereo viewport mode\n")	\
+		VERB("                                    1: above/below half-height format\n")	\
+		VERB("                                    2: side/by/side half-width format\n")	\
+		VERB("                                    3: side/by/side half-size format, normal aspect ratio\n") \
 	)	\
 	DXX_if_defined_01(DXX_USE_UDP, (	\
 		VERB("\n Multiplayer:\n\n")	\
diff --git a/similar/misc/args.cpp b/similar/misc/args.cpp
index df5752f0a..f04519bf3 100644
--- a/similar/misc/args.cpp
+++ b/similar/misc/args.cpp
@@ -295,6 +295,8 @@ static void ReadCmdArgs(Inilist &ini, Arglist &Args)
 			CGameArg.OglDarkEdges = true;
 		else if (!d_stricmp(p, "-gl_stereo"))
 			CGameArg.OglStereo = true;
+		else if (!d_stricmp(p, "-gl_stereoview"))
+			CGameArg.OglStereoView = arg_integer(pp, end);
 #endif
 
 	// Multiplayer Options