AGS: Updated Multitasking setting

* Added `[misc] multitasking=[0,1]` to config, acting as a *starting*
  setting, which may be changed by runtime call to `SetMultitaskingMode`;
* Ensure multitasking mode is overridden by connected external debugger
  (always on, if possible);
* Let multitasking mode work in "fullscreen desktop" gfx mode (still
  disabled in exclusive fullscreen);
* Now correctly reset multitasking mode if gfx mode changes.

From upstream 9f091926e393f75c90c951f9597710bf17395332

engines/ags/engine/ac/game.cpp

@@ -1219,9 +1219,6 @@ void display_switch_out_suspend() {
 		}
 	}
 
-	// restore the callbacks
-	SetMultitasking(0);
-
 	_G(switching_away_from_game)--;
 }
 

engines/ags/engine/ac/game_setup.h

@@ -92,6 +92,7 @@ struct GameSetup {
 	bool  load_latest_save; // load latest saved game on launch
 	ScreenRotation rotation;
 	bool  show_fps;
+	bool  multitasking = false; // whether run on background, when game is switched out
 
 	DisplayModeSetup Screen;
 	String software_render_driver;

engines/ags/engine/ac/global_game.cpp

@@ -643,19 +643,26 @@ void SetMultitasking(int mode) {
 	if ((mode < 0) | (mode > 1))
 		quit("!SetMultitasking: invalid mode parameter");
 
-	if (_GP(usetup).override_multitasking >= 0) {
+	// Account for the override config option (must be checked first!)
+	if ((_GP(usetup).override_multitasking >= 0) && (mode != _GP(usetup).override_multitasking)) {
 		Debug::Printf("SetMultitasking: overridden by user config: %d -> %d", mode, _GP(usetup).override_multitasking);
 		mode = _GP(usetup).override_multitasking;
 	}
 
-	// Don't allow background running if full screen
-	if ((mode == 1) && (!_GP(scsystem).windowed)) {
-		Debug::Printf("SetMultitasking: overridden by fullscreen: %d -> %d", mode, 0);
+	// Must run on background if debugger is connected
+	if ((mode == 0) && (_G(editor_debugging_initialized) != 0)) {
+		Debug::Printf("SetMultitasking: overridden by the external debugger: %d -> 1", mode);
+		mode = 1;
+	}
+
+	// Regardless, don't allow background running if exclusive full screen
+	if ((mode == 1) && _G(gfxDriver)->GetDisplayMode().IsRealFullscreen()) {
+		Debug::Printf("SetMultitasking: overridden by fullscreen: %d -> 0", mode);
 		mode = 0;
 	}
 
 	// Install engine callbacks for switching in and out the window
-	Debug::Printf("SetMultitasking: mode %d", mode);
+	Debug::Printf(kDbgMsg_Info, "Multitasking mode set: %d", mode);
 	if (mode == 0) {
 		sys_set_background_mode(false);
 		sys_evt_set_focus_callbacks(display_switch_in_resume, display_switch_out_suspend);

engines/ags/engine/main/config.cpp

@@ -349,6 +349,9 @@ void apply_config(const ConfigTree &cfg) {
 			}
 		}
 
+		// Various system options
+		_GP(usetup).multitasking = CfgReadInt(cfg, "misc", "multitasking", 0) != 0;
+
 		// User's overrides and hacks
 		_GP(usetup).override_multitasking = CfgReadInt(cfg, "override", "multitasking", -1);
 		String override_os = CfgReadString(cfg, "override", "os");

engines/ags/engine/main/engine.cpp

@@ -1176,7 +1176,7 @@ int initialize_engine(const ConfigTree &startup_opts) {
 	// Configure game window after renderer was initialized
 	engine_setup_window();
 
-	SetMultitasking(0);
+	SetMultitasking(_GP(usetup).multitasking);
 
 	sys_window_show_cursor(false); // hide the system cursor
 

engines/ags/engine/main/engine_setup.cpp

@@ -27,6 +27,7 @@
 #include "ags/engine/ac/game_setup.h"
 #include "ags/shared/ac/game_setup_struct.h"
 #include "ags/engine/ac/game_state.h"
+#include "ags/engine/ac/global_game.h"
 #include "ags/engine/ac/mouse.h"
 #include "ags/engine/ac/runtime_defines.h"
 #include "ags/engine/ac/walk_behind.h"
@@ -270,6 +271,9 @@ void engine_post_gfxmode_setup(const Size &init_desktop) {
 	}
 	engine_post_gfxmode_mouse_setup(init_desktop);
 
+	// reset multitasking (may be overridden by the current display mode)
+	SetMultitasking(_GP(usetup).multitasking);
+
 	invalidate_screen();
 }
 

engines/ags/engine/main/game_start.cpp

@@ -26,6 +26,7 @@
 #include "ags/shared/ac/common.h"
 #include "ags/shared/ac/character_info.h"
 #include "ags/engine/ac/game.h"
+#include "ags/engine/ac/game_setup.h"
 #include "ags/shared/ac/game_setup_struct.h"
 #include "ags/engine/ac/game_setup.h"
 #include "ags/engine/ac/game_state.h"
@@ -57,6 +58,7 @@ void start_game_init_editor_debugging() {
 		return;
 
 	// Debugger expects strict multitasking
+	_GP(usetup).multitasking = true;
 	_GP(usetup).override_multitasking = -1;
 	SetMultitasking(1);
 

engines/ags/engine/main/graphics_mode.cpp

@@ -473,8 +473,9 @@ bool graphics_mode_set_dm(const DisplayMode &dm) {
 		_GP(SavedWindowedSetting).Dm = rdm;
 	else
 		_GP(SavedFullscreenSetting).Dm = rdm;
-	Debug::Printf("Succeeded. Using gfx mode %d x %d (%d-bit) %s",
-		rdm.Width, rdm.Height, rdm.ColorDepth, rdm.IsWindowed() ? "windowed" : "fullscreen");
+	Debug::Printf(kDbgMsg_Info, "Graphics mode set: %d x %d (%d-bit) %s",
+		rdm.Width, rdm.Height, rdm.ColorDepth,
+		rdm.IsWindowed() ? "windowed" : (rdm.IsRealFullscreen() ? "fullscreen" : "fullscreen desktop"));
 	return true;
 }