diff --git a/neo/CMakeLists.txt b/neo/CMakeLists.txt
index 5d31f19a..53f97890 100644
--- a/neo/CMakeLists.txt
+++ b/neo/CMakeLists.txt
@@ -1224,6 +1224,9 @@ include_directories(${CMAKE_BINARY_DIR})
 include_directories(${CMAKE_SOURCE_DIR})
 
 add_library(idlib STATIC ${src_idlib})
+if(SDL3)
+	target_link_libraries(idlib SDL3::Headers) # so it can use SDL_Endian.h
+endif()
 if (AROS)
 	add_library(dll STATIC ${src_arosdll})
         if(CMAKE_SYSTEM_PROCESSOR STREQUAL "i386")
diff --git a/neo/framework/Common.cpp b/neo/framework/Common.cpp
index 95d11fb2..76101066 100644
--- a/neo/framework/Common.cpp
+++ b/neo/framework/Common.cpp
@@ -26,7 +26,13 @@ If you have questions concerning this license or the applicable additional terms
 ===========================================================================
 */
 
-#include <SDL.h>
+#ifdef D3_SDL3
+  #include <SDL3/SDL.h>
+  // DG: compat with SDL2
+  #define SDL_setenv SDL_setenv_unsafe
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+#endif
 
 #include "sys/platform.h"
 #include "idlib/containers/HashTable.h"
@@ -2799,7 +2805,12 @@ void idCommonLocal::SetMachineSpec( void ) {
 	}
 }
 
-static unsigned int AsyncTimer(unsigned int interval, void *) {
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+static Uint32 AsyncTimer(void * /*userdata*/, SDL_TimerID /* timerID */, Uint32 interval)
+#else // SDL2 or SDL1.2
+static unsigned int AsyncTimer(unsigned int interval, void *)
+#endif
+{
 	common->Async();
 	Sys_TriggerEvent(TRIGGER_EVENT_ONE);
 
@@ -2947,13 +2958,19 @@ void idCommonLocal::Init( int argc, char **argv ) {
 #endif
 #endif
 
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	if ( ! SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK | SDL_INIT_GAMEPAD) )
+	{
+		if ( SDL_Init(SDL_INIT_VIDEO) ) { // retry without joystick/gamepad if it failed
+			Sys_Printf( "WARNING: Couldn't get SDL gamepad support! Gamepads won't work!\n" );
+		} else
+#elif SDL_VERSION_ATLEAST(2, 0, 0)
 	if (SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO | SDL_INIT_JOYSTICK | SDL_INIT_GAMECONTROLLER) != 0)
 	{
 		if (SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO) == 0) { // retry without joystick/gamecontroller if it failed
 			Sys_Printf( "WARNING: Couldn't get SDL gamecontroller support! Gamepads won't work!\n" );
 		} else
-#else
+#else // SDL1.2
 	if (SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO) != 0) // no gamecontroller support in SDL1
 	{
 #endif
@@ -3005,14 +3022,22 @@ void idCommonLocal::Init( int argc, char **argv ) {
 		idCVar::RegisterStaticVars();
 
 		// print engine version
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+		int sdlv = SDL_GetVersion();
+		int sdlvmaj = SDL_VERSIONNUM_MAJOR(sdlv);
+		int sdlvmin = SDL_VERSIONNUM_MINOR(sdlv);
+		int sdlvmicro = SDL_VERSIONNUM_MICRO(sdlv);
+		Printf( "%s using SDL v%d.%d.%d\n", version.string, sdlvmaj, sdlvmin, sdlvmicro );
+#else
+  #if SDL_VERSION_ATLEAST(2, 0, 0)
 		SDL_version sdlv;
 		SDL_GetVersion(&sdlv);
-#else
+  #else
 		SDL_version sdlv = *SDL_Linked_Version();
-#endif
+  #endif
 		Printf( "%s using SDL v%u.%u.%u\n",
 				version.string, sdlv.major, sdlv.minor, sdlv.patch );
+#endif
 
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 		Printf( "SDL video driver: %s\n", SDL_GetCurrentVideoDriver() );
diff --git a/neo/framework/Dhewm3SettingsMenu.cpp b/neo/framework/Dhewm3SettingsMenu.cpp
index 66d654a4..27aa963b 100644
--- a/neo/framework/Dhewm3SettingsMenu.cpp
+++ b/neo/framework/Dhewm3SettingsMenu.cpp
@@ -2,7 +2,11 @@
 
 #include <algorithm> // std::sort - TODO: replace with something custom..
 
-#include <SDL.h> // to show display size
+#ifdef D3_SDL3
+  #include <SDL3/SDL.h>
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+#endif
 
 #define IMGUI_DEFINE_MATH_OPERATORS
 
@@ -1903,9 +1907,15 @@ static void DrawVideoOptionsMenu()
 	}
 
 	// resolution info text
-	int sdlDisplayIdx = SDL_GetWindowDisplayIndex( SDL_GL_GetCurrentWindow() );
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	// in SDL3 it's a Display ID, in SDL2 a Display Index, in both cases the value
+	// can be fed into SDL_GetDisplayBounds()
+	SDL_DisplayID sdlDisplayId_x = SDL_GetDisplayForWindow( SDL_GL_GetCurrentWindow() );
+#else // SDL2
+	int sdlDisplayId_x = SDL_GetWindowDisplayIndex( SDL_GL_GetCurrentWindow() );
+#endif
 	SDL_Rect displayRect = {};
-	SDL_GetDisplayBounds( sdlDisplayIdx, &displayRect );
+	SDL_GetDisplayBounds( sdlDisplayId_x, &displayRect );
 	if ( (int)glConfig.winWidth != glConfig.vidWidth ) {
 		ImGui::TextDisabled( "Current Resolution: %g x %g (Physical: %d x %d)",
 		                     glConfig.winWidth, glConfig.winHeight, glConfig.vidWidth, glConfig.vidHeight );
diff --git a/neo/renderer/qgl.h b/neo/renderer/qgl.h
index 64177009..abce7a8e 100644
--- a/neo/renderer/qgl.h
+++ b/neo/renderer/qgl.h
@@ -42,7 +42,11 @@ If you have questions concerning this license or the applicable additional terms
 	#endif
 #endif
 
-#include <SDL_opengl.h>
+#ifdef D3_SDL3
+  #include <SDL3/SDL_opengl.h>
+#else // SDL1.2 or SDL2
+  #include <SDL_opengl.h>
+#endif
 
 #if defined( ID_DEDICATED ) && defined( _WIN32 )
 // restore WINGDIAPI
diff --git a/neo/sys/cpu.cpp b/neo/sys/cpu.cpp
index 56a06dcf..c7f9e235 100644
--- a/neo/sys/cpu.cpp
+++ b/neo/sys/cpu.cpp
@@ -28,7 +28,14 @@ If you have questions concerning this license or the applicable additional terms
 
 #include <float.h>
 
-#include <SDL_cpuinfo.h>
+#ifdef D3_SDL3
+  #include <SDL3/SDL_cpuinfo.h>
+  // in SDL3, SDL_Has3DNow() has been removed, and nowadays it's not really relevant anyway,
+  // so just replace it with 0/false
+  #define SDL_Has3DNow() 0
+#else // SDL1.2 or SDL2
+  #include <SDL_cpuinfo.h>
+#endif
 
 // MSVC header intrin.h uses strcmp and errors out when not set
 #define IDSTR_NO_REDIRECT
diff --git a/neo/sys/events.cpp b/neo/sys/events.cpp
index b0c77ef8..184e9535 100644
--- a/neo/sys/events.cpp
+++ b/neo/sys/events.cpp
@@ -26,7 +26,13 @@ If you have questions concerning this license or the applicable additional terms
 ===========================================================================
 */
 
-#include <SDL.h>
+#ifdef D3_SDL3
+  // HACK: I don't want SDL.h to drag in SDL_oldnames.h to avoid all the warnings about redefined definitions
+  #define SDL_oldnames_h_
+  #include <SDL3/SDL.h>
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+#endif
 
 #include "sys/platform.h"
 #include "idlib/containers/List.h"
@@ -61,6 +67,109 @@ If you have questions concerning this license or the applicable additional terms
 #define SDLK_PRINTSCREEN SDLK_PRINT
 #endif
 
+// unholy hacks to make it work with SDL3 (and also SDL2 and partly SDL1.2)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+  // in SDL3 SDL_GetKeyFromScancode() got additional arguments that I don't care about
+  #define SDL_GetKeyFromScancode(SC)  SDL_GetKeyFromScancode(SC, 0, true)
+
+  #define SDLK_z SDLK_Z
+
+  #define SDL_TEXTINPUT SDL_EVENT_TEXT_INPUT
+  #define SDL_KEYDOWN SDL_EVENT_KEY_DOWN
+  #define SDL_KEYUP SDL_EVENT_KEY_UP
+
+  #define SDL_USEREVENT SDL_EVENT_USER
+  #define SDL_QUIT SDL_EVENT_QUIT
+
+  #define SDL_MOUSEBUTTONDOWN SDL_EVENT_MOUSE_BUTTON_DOWN
+  #define SDL_MOUSEBUTTONUP SDL_EVENT_MOUSE_BUTTON_UP
+  #define SDL_MOUSEMOTION SDL_EVENT_MOUSE_MOTION
+  #define SDL_MOUSEWHEEL SDL_EVENT_MOUSE_WHEEL
+
+  #define SDL_JoystickGUID SDL_GUID
+  #define SDL_JoystickGetGUID SDL_GetJoystickGUID
+  #define SDL_JoystickName SDL_GetJoystickName
+  #define SDL_JoystickGetGUIDString SDL_GUIDToString
+
+  #define SDL_JOYDEVICEADDED SDL_EVENT_JOYSTICK_ADDED
+  #define SDL_JOYDEVICEREMOVED SDL_EVENT_JOYSTICK_REMOVED
+
+  // game controllers have been renamed to gamepads and the
+  // corresponding SDL_Event members are now prefixed with g instead of c
+  #define cbutton gbutton
+  #define caxis gaxis
+
+  #define SDL_GameController SDL_Gamepad
+  #define SDL_GameControllerAxis SDL_GamepadAxis
+  #define SDL_GameControllerButton SDL_GamepadButton
+
+  #define SDL_GameControllerGetType SDL_GetGamepadType
+  #define SDL_GameControllerName SDL_GetGamepadName
+  #define SDL_GameControllerGetJoystick SDL_GetGamepadJoystick
+  #define SDL_GameControllerGetVendor SDL_GetGamepadVendor
+  #define SDL_GameControllerGetProduct SDL_GetGamepadProduct
+  #define SDL_GameControllerOpen SDL_OpenGamepad
+
+  #define SDL_CONTROLLERAXISMOTION SDL_EVENT_GAMEPAD_AXIS_MOTION
+  #define SDL_CONTROLLERBUTTONDOWN SDL_EVENT_GAMEPAD_BUTTON_DOWN
+  #define SDL_CONTROLLERBUTTONUP SDL_EVENT_GAMEPAD_BUTTON_UP
+
+  #define SDL_CONTROLLER_AXIS_LEFTX SDL_GAMEPAD_AXIS_LEFTX
+  #define SDL_CONTROLLER_AXIS_LEFTY SDL_GAMEPAD_AXIS_LEFTY
+  #define SDL_CONTROLLER_AXIS_MAX SDL_GAMEPAD_AXIS_MAX
+  #define SDL_CONTROLLER_AXIS_RIGHTX SDL_GAMEPAD_AXIS_RIGHTX
+  #define SDL_CONTROLLER_AXIS_RIGHTY SDL_GAMEPAD_AXIS_RIGHTY
+  #define SDL_CONTROLLER_AXIS_TRIGGERLEFT SDL_GAMEPAD_AXIS_LEFT_TRIGGER
+  #define SDL_CONTROLLER_AXIS_TRIGGERRIGHT SDL_GAMEPAD_AXIS_RIGHT_TRIGGER
+  //#define SDL_CONTROLLER_BINDTYPE_AXIS SDL_GAMEPAD_BINDTYPE_AXIS
+  //#define SDL_CONTROLLER_BINDTYPE_BUTTON SDL_GAMEPAD_BINDTYPE_BUTTON
+  //#define SDL_CONTROLLER_BINDTYPE_HAT SDL_GAMEPAD_BINDTYPE_HAT
+  //#define SDL_CONTROLLER_BINDTYPE_NONE SDL_GAMEPAD_BINDTYPE_NONE
+  #define SDL_CONTROLLER_BUTTON_A SDL_GAMEPAD_BUTTON_SOUTH
+  #define SDL_CONTROLLER_BUTTON_B SDL_GAMEPAD_BUTTON_EAST
+  #define SDL_CONTROLLER_BUTTON_X SDL_GAMEPAD_BUTTON_WEST
+  #define SDL_CONTROLLER_BUTTON_Y SDL_GAMEPAD_BUTTON_NORTH
+  #define SDL_CONTROLLER_BUTTON_BACK SDL_GAMEPAD_BUTTON_BACK
+  #define SDL_CONTROLLER_BUTTON_DPAD_DOWN SDL_GAMEPAD_BUTTON_DPAD_DOWN
+  #define SDL_CONTROLLER_BUTTON_DPAD_LEFT SDL_GAMEPAD_BUTTON_DPAD_LEFT
+  #define SDL_CONTROLLER_BUTTON_DPAD_RIGHT SDL_GAMEPAD_BUTTON_DPAD_RIGHT
+  #define SDL_CONTROLLER_BUTTON_DPAD_UP SDL_GAMEPAD_BUTTON_DPAD_UP
+  #define SDL_CONTROLLER_BUTTON_GUIDE SDL_GAMEPAD_BUTTON_GUIDE
+  #define SDL_CONTROLLER_BUTTON_INVALID SDL_GAMEPAD_BUTTON_INVALID
+  #define SDL_CONTROLLER_BUTTON_LEFTSHOULDER SDL_GAMEPAD_BUTTON_LEFT_SHOULDER
+  #define SDL_CONTROLLER_BUTTON_LEFTSTICK SDL_GAMEPAD_BUTTON_LEFT_STICK
+  #define SDL_CONTROLLER_BUTTON_MISC1 SDL_GAMEPAD_BUTTON_MISC1
+  #define SDL_CONTROLLER_BUTTON_PADDLE1 SDL_GAMEPAD_BUTTON_RIGHT_PADDLE1
+  #define SDL_CONTROLLER_BUTTON_PADDLE2 SDL_GAMEPAD_BUTTON_LEFT_PADDLE1
+  #define SDL_CONTROLLER_BUTTON_PADDLE3 SDL_GAMEPAD_BUTTON_RIGHT_PADDLE2
+  #define SDL_CONTROLLER_BUTTON_PADDLE4 SDL_GAMEPAD_BUTTON_LEFT_PADDLE2
+  #define SDL_CONTROLLER_BUTTON_RIGHTSHOULDER SDL_GAMEPAD_BUTTON_RIGHT_SHOULDER
+  #define SDL_CONTROLLER_BUTTON_RIGHTSTICK SDL_GAMEPAD_BUTTON_RIGHT_STICK
+  #define SDL_CONTROLLER_BUTTON_START SDL_GAMEPAD_BUTTON_START
+  #define SDL_CONTROLLER_BUTTON_TOUCHPAD SDL_GAMEPAD_BUTTON_TOUCHPAD
+
+  #define SDL_CONTROLLER_TYPE_NINTENDO_SWITCH_JOYCON_LEFT SDL_GAMEPAD_TYPE_NINTENDO_SWITCH_JOYCON_LEFT
+  #define SDL_CONTROLLER_TYPE_NINTENDO_SWITCH_JOYCON_PAIR SDL_GAMEPAD_TYPE_NINTENDO_SWITCH_JOYCON_PAIR
+  #define SDL_CONTROLLER_TYPE_NINTENDO_SWITCH_JOYCON_RIGHT SDL_GAMEPAD_TYPE_NINTENDO_SWITCH_JOYCON_RIGHT
+  #define SDL_CONTROLLER_TYPE_NINTENDO_SWITCH_PRO SDL_GAMEPAD_TYPE_NINTENDO_SWITCH_PRO
+  #define SDL_CONTROLLER_TYPE_PS3 SDL_GAMEPAD_TYPE_PS3
+  #define SDL_CONTROLLER_TYPE_PS4 SDL_GAMEPAD_TYPE_PS4
+  #define SDL_CONTROLLER_TYPE_PS5 SDL_GAMEPAD_TYPE_PS5
+  #define SDL_CONTROLLER_TYPE_UNKNOWN SDL_GAMEPAD_TYPE_STANDARD
+  #define SDL_CONTROLLER_TYPE_VIRTUAL SDL_GAMEPAD_TYPE_VIRTUAL
+  #define SDL_CONTROLLER_TYPE_XBOX360 SDL_GAMEPAD_TYPE_XBOX360
+  #define SDL_CONTROLLER_TYPE_XBOXONE SDL_GAMEPAD_TYPE_XBOXONE
+
+  #define IS_SDL_BTN_DOWN(EV)  EV.down
+
+  // FIXME: at some point I need to enable (and possibly later disable) SDL_TextInput!
+
+#else // SDL2 and SDL1.2
+
+  #define IS_SDL_BTN_DOWN(EV)  (EV.state == SDL_PRESSED)
+
+#endif // SDL_VERSION_ATLEAST(3, 0, 0) - unholy hacks
+
 extern idCVar in_useGamepad; // from UsercmdGen.cpp
 extern idCVar joy_deadZone;  // ditto
 
@@ -78,7 +187,7 @@ static idCVar in_ignoreConsoleKey("in_ignoreConsoleKey", "0", CVAR_SYSTEM | CVAR
 		"Console only opens with Shift+Esc, not ` or ^ etc");
 
 static idCVar in_nograb("in_nograb", "0", CVAR_SYSTEM | CVAR_NOCHEAT, "prevents input grabbing");
-static idCVar in_grabKeyboard("in_grabKeyboard", "0", CVAR_SYSTEM | CVAR_ARCHIVE | CVAR_NOCHEAT | CVAR_BOOL,
+idCVar in_grabKeyboard("in_grabKeyboard", "0", CVAR_SYSTEM | CVAR_ARCHIVE | CVAR_NOCHEAT | CVAR_BOOL,
 		"if enabled, grabs all keyboard input if mouse is grabbed (so keyboard shortcuts from the OS like Alt-Tab or Windows Key won't work)");
 
 idCVar joy_gamepadLayout("joy_gamepadLayout", "-1", CVAR_SYSTEM | CVAR_ARCHIVE | CVAR_NOCHEAT | CVAR_INTEGER,
@@ -100,7 +209,7 @@ struct kbd_poll_t {
 	int key;
 	bool state;
 
-	kbd_poll_t() {
+	kbd_poll_t() : key(0), state(false) {
 	}
 
 	kbd_poll_t(int k, bool s) {
@@ -113,7 +222,7 @@ struct mouse_poll_t {
 	int action;
 	int value;
 
-	mouse_poll_t() {
+	mouse_poll_t() : action(0), value(0) {
 	}
 
 	mouse_poll_t(int a, int v) {
@@ -269,10 +378,11 @@ const char* Sys_GetLocalizedJoyKeyName( int key ) {
 	if (key >= K_FIRST_JOY && key <= K_LAST_JOY) {
 
 		if (key <= K_JOY_BTN_BACK) {
-#if SDL_VERSION_ATLEAST(3, 0, 0)
+#if 0 //SDL_VERSION_ATLEAST(3, 0, 0)
 			// TODO: or use the SDL2 code and just set joy_gamepadLayout automatically based on SDL_GetGamepadType() ?
-			SDL_GamepadButton gpbtn = SDL_GAMEPAD_BUTTON_SOUTH + (key - K_JOY_BTN_SOUTH);
-			SDL_GamepadButtonLabel label = SDL_GetGamepadButtonLabelForType(TODO, gpbtn);
+			SDL_GamepadButton gpbtn = (SDL_GamepadButton)(SDL_GAMEPAD_BUTTON_SOUTH + (key - K_JOY_BTN_SOUTH));
+			SDL_GamepadType sdlGamepadType = TODO;
+			SDL_GamepadButtonLabel label = SDL_GetGamepadButtonLabelForType(sdlGamepadType, gpbtn);
 			switch(label) {
 				case SDL_GAMEPAD_BUTTON_LABEL_A:
 					return "Pad A";
@@ -844,7 +954,8 @@ void Sys_InitInput() {
 	in_kbd.SetModified();
 	Sys_GetConsoleKey(false); // initialize consoleKeymappingIdx from in_kbd
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	const char* grabKeyboardEnv = SDL_getenv(SDL_HINT_GRAB_KEYBOARD);
+	// NOTE: SDL3 doesn't support that hint/env var, but whatever, support the env var anyway
+	const char* grabKeyboardEnv = SDL_getenv("SDL_GRAB_KEYBOARD");
 	if ( grabKeyboardEnv ) {
 		common->Printf( "The SDL_GRAB_KEYBOARD environment variable is set, setting the in_grabKeyboard CVar to the same value (%s)\n", grabKeyboardEnv );
 		in_grabKeyboard.SetString( grabKeyboardEnv );
@@ -861,7 +972,19 @@ void Sys_InitInput() {
 	memset( buttonStates, 0, sizeof( buttonStates ) );
 	memset( joyAxis, 0, sizeof( joyAxis ) );
 
-#if SDL_VERSION_ATLEAST(2, 0, 0) // gamecontroller/gamepad not supported in SDL1
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	int numJoysticks = 0;
+	SDL_JoystickID* joysticks = SDL_GetJoysticks(&numJoysticks);
+	for( int i = 0; i < numJoysticks; ++i )
+	{
+		SDL_GameController* gc = SDL_GameControllerOpen( joysticks[i] );
+		if ( gc != NULL ) {
+			setGamepadType( gc );
+		}
+	}
+	SDL_free(joysticks);
+
+#elif SDL_VERSION_ATLEAST(2, 0, 0)
 	// use button positions instead of button labels,
 	// Sys_GetLocalizedJoyKeyName() will do the translation
 	// (I think this also was the default before 2.0.12?)
@@ -875,7 +998,7 @@ void Sys_InitInput() {
 			setGamepadType( gc );
 		}
 	}
-#endif
+#endif // gamecontroller/gamepad not supported in SDL1
 }
 
 /*
@@ -1082,6 +1205,7 @@ sysEvent_t Sys_GetEvent() {
 	SDL_Event ev;
 	sysEvent_t res = { };
 	int key;
+	bool isDown = false;
 
 	static const sysEvent_t res_none = { SE_NONE, 0, 0, 0, NULL };
 
@@ -1094,7 +1218,9 @@ sysEvent_t Sys_GetEvent() {
 	}
 
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	static char s[SDL_TEXTINPUTEVENT_TEXT_SIZE] = {0};
+	// s used to have SDL_TEXTINPUTEVENT_TEXT_SIZE (32) bytes, but in SDL3 the string can have
+	// arbitrary size, however I assume that 128 should still be more than enough
+	static char s[128] = {0};
 	static size_t s_pos = 0;
 
 	if (s[0] != '\0') {
@@ -1103,7 +1229,7 @@ sysEvent_t Sys_GetEvent() {
 
 		++s_pos;
 
-		if (!s[s_pos] || s_pos == SDL_TEXTINPUTEVENT_TEXT_SIZE) {
+		if (!s[s_pos] || s_pos == sizeof(s)) {
 			memset(s, 0, sizeof(s));
 			s_pos = 0;
 		}
@@ -1131,7 +1257,36 @@ sysEvent_t Sys_GetEvent() {
 		}
 
 		switch (ev.type) {
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+			case SDL_EVENT_WINDOW_FOCUS_GAINED: {
+					// unset modifier, in case alt-tab was used to leave window and ALT is still set
+					// as that can cause fullscreen-toggling when pressing enter...
+					SDL_Keymod currentmod = SDL_GetModState();
+
+					int newmod = SDL_KMOD_NONE;
+					if (currentmod & SDL_KMOD_CAPS) // preserve capslock
+						newmod |= SDL_KMOD_CAPS;
+
+					SDL_SetModState((SDL_Keymod)newmod);
+				} // new context because visual studio complains about newmod and currentmod not initialized because of the case SDL_WINDOWEVENT_FOCUS_LOST
+
+
+				in_hasFocus = true;
+
+				// start playing the game sound world again (when coming from editor)
+				session->SetPlayingSoundWorld();
+				continue; // handle next event
+
+			case SDL_EVENT_WINDOW_FOCUS_LOST:
+				in_hasFocus = false;
+				continue; // handle next event
+
+			case SDL_EVENT_WINDOW_RESIZED:
+			case SDL_EVENT_WINDOW_PIXEL_SIZE_CHANGED:
+				GLimp_UpdateWindowSize();
+				continue;  // handle next event
+
+#elif SDL_VERSION_ATLEAST(2, 0, 0)
 		case SDL_WINDOWEVENT:
 			switch (ev.window.event) {
 				case SDL_WINDOWEVENT_FOCUS_GAINED: {
@@ -1188,7 +1343,11 @@ sysEvent_t Sys_GetEvent() {
 #endif
 
 		case SDL_KEYDOWN:
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+			if (ev.key.key == SDLK_RETURN && (ev.key.mod & SDL_KMOD_ALT) > 0) {
+#else
 			if (ev.key.keysym.sym == SDLK_RETURN && (ev.key.keysym.mod & KMOD_ALT) > 0) {
+#endif
 				cvarSystem->SetCVarBool("r_fullscreen", !renderSystem->IsFullScreen());
 				PushConsoleEvent("vid_restart partial");
 				return res_none;
@@ -1213,12 +1372,18 @@ sysEvent_t Sys_GetEvent() {
 					continue; // handle next event
 				}
 			}
-#else
+#else // SDL2+
 		{
+	#if SDL_VERSION_ATLEAST(3, 0, 0)
+			SDL_Scancode sc = ev.key.scancode;
+			SDL_Keycode keycode = ev.key.key;
+	#else // SDL2
+			SDL_Scancode sc = ev.key.keysym.scancode;
+			SDL_Keycode keycode = ev.key.keysym.sym;
+	#endif
 			// workaround for AZERTY-keyboards, which don't have 1, 2, ..., 9, 0 in first row:
 			// always map those physical keys (scancodes) to those keycodes anyway
 			// see also https://bugzilla.libsdl.org/show_bug.cgi?id=3188
-			SDL_Scancode sc = ev.key.keysym.scancode;
 			if(sc == SDL_SCANCODE_0)
 			{
 				key = '0';
@@ -1232,10 +1397,10 @@ sysEvent_t Sys_GetEvent() {
 			}
 			else
 			{
-				key = mapkey(ev.key.keysym.sym);
+				key = mapkey(keycode);
 			}
 
-			if ( !in_ignoreConsoleKey.GetBool() && ev.key.keysym.scancode == SDL_SCANCODE_GRAVE ) {
+			if ( !in_ignoreConsoleKey.GetBool() && sc == SDL_SCANCODE_GRAVE ) {
 				// that key between Esc, Tab and 1 is the console key
 				key = K_CONSOLE;
 			}
@@ -1245,22 +1410,23 @@ sysEvent_t Sys_GetEvent() {
 				key = getKeynumForSDLscancode(sc);
 				if(!key) {
 					if (ev.type == SDL_KEYDOWN) {
-						common->Warning("unmapped SDL key %d (scancode %d)", ev.key.keysym.sym, (int)sc);
+						common->Warning("unmapped SDL key %d (scancode %d)", keycode, (int)sc);
 					}
 					continue; // handle next event
 				}
 			}
 		}
 #endif
+			isDown = IS_SDL_BTN_DOWN( ev.key );
 
 			res.evType = SE_KEY;
 			res.evValue = key;
-			res.evValue2 = ev.key.state == SDL_PRESSED ? 1 : 0;
+			res.evValue2 = isDown;
 
-			kbd_polls.Append(kbd_poll_t(key, ev.key.state == SDL_PRESSED));
+			kbd_polls.Append( kbd_poll_t( key, isDown ) );
 
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-			if (key == K_BACKSPACE && ev.key.state == SDL_PRESSED)
+			if (key == K_BACKSPACE && isDown)
 				c = key;
 #else
 			if (ev.key.state == SDL_PRESSED && (ev.key.keysym.unicode & 0xff00) == 0)
@@ -1277,7 +1443,14 @@ sysEvent_t Sys_GetEvent() {
 				if ( isAscii(ev.text.text) ) {
 					res.evValue = ev.text.text[0];
 					if ( ev.text.text[1] != '\0' ) {
+	#if SDL_VERSION_ATLEAST(3, 0, 0)
+						// yes, it's ok if this is not 0-terminated, the code generating
+						// events from s handles that
+						strncpy(s, ev.text.text, sizeof(s));
+	#else // SDL2
 						memcpy( s, ev.text.text, SDL_TEXTINPUTEVENT_TEXT_SIZE );
+						s[SDL_TEXTINPUTEVENT_TEXT_SIZE] = '\0';
+	#endif
 						s_pos = 1; // pos 0 is returned
 					}
 					return res;
@@ -1294,10 +1467,6 @@ sysEvent_t Sys_GetEvent() {
 			}
 
 			continue; // handle next event
-
-		case SDL_TEXTEDITING:
-			// on windows we get this event whenever the window gains focus.. just ignore it.
-			continue;
 #endif
 
 		case SDL_MOUSEMOTION:
@@ -1335,20 +1504,21 @@ sysEvent_t Sys_GetEvent() {
 
 		case SDL_MOUSEBUTTONDOWN:
 		case SDL_MOUSEBUTTONUP:
+			isDown = IS_SDL_BTN_DOWN(ev.button);
 			res.evType = SE_KEY;
 
 			switch (ev.button.button) {
 			case SDL_BUTTON_LEFT:
 				res.evValue = K_MOUSE1;
-				mouse_polls.Append(mouse_poll_t(M_ACTION1, ev.button.state == SDL_PRESSED ? 1 : 0));
+				mouse_polls.Append(mouse_poll_t(M_ACTION1, isDown));
 				break;
 			case SDL_BUTTON_MIDDLE:
 				res.evValue = K_MOUSE3;
-				mouse_polls.Append(mouse_poll_t(M_ACTION3, ev.button.state == SDL_PRESSED ? 1 : 0));
+				mouse_polls.Append(mouse_poll_t(M_ACTION3, isDown));
 				break;
 			case SDL_BUTTON_RIGHT:
 				res.evValue = K_MOUSE2;
-				mouse_polls.Append(mouse_poll_t(M_ACTION2, ev.button.state == SDL_PRESSED ? 1 : 0));
+				mouse_polls.Append(mouse_poll_t(M_ACTION2, isDown));
 				break;
 
 #if !SDL_VERSION_ATLEAST(2, 0, 0)
@@ -1370,14 +1540,14 @@ sysEvent_t Sys_GetEvent() {
 				{
 					int buttonIndex = ev.button.button - SDL_BUTTON_LEFT;
 					res.evValue = K_MOUSE1 + buttonIndex;
-					mouse_polls.Append( mouse_poll_t( M_ACTION1 + buttonIndex, ev.button.state == SDL_PRESSED ? 1 : 0 ) );
+					mouse_polls.Append( mouse_poll_t( M_ACTION1 + buttonIndex, isDown ) );
 				}
 				else
 #endif
 				continue; // handle next event
 			}
 
-			res.evValue2 = ev.button.state == SDL_PRESSED ? 1 : 0;
+			res.evValue2 = isDown;
 
 			return res;
 
@@ -1390,8 +1560,10 @@ sysEvent_t Sys_GetEvent() {
 				continue;
 			}
 
+			isDown = IS_SDL_BTN_DOWN(ev.cbutton);
+
 			res.evType = SE_KEY;
-			res.evValue2 = ev.cbutton.state == SDL_PRESSED ? 1 : 0;
+			res.evValue2 = isDown;
 
 			// special case: always treat the start button as escape so it opens/closes the menu
 			// (also makes that button non-bindable)
@@ -1410,7 +1582,7 @@ sysEvent_t Sys_GetEvent() {
 			}
 
 			sys_jEvents jEvent =  mapjoybutton( (SDL_GameControllerButton)ev.cbutton.button );
-			joystick_polls.Append( joystick_poll_t(jEvent, ev.cbutton.state == SDL_PRESSED ? 1 : 0) );
+			joystick_polls.Append( joystick_poll_t(jEvent, isDown) );
 
 			if ( ( jEvent >= J_ACTION_FIRST ) && ( jEvent <= J_ACTION_MAX ) ) {
 				res.evValue = K_FIRST_JOY + ( jEvent - J_ACTION_FIRST );
@@ -1630,7 +1802,8 @@ void Sys_GenerateEvents() {
 	if (s)
 		PushConsoleEvent(s);
 
-#ifndef ID_DEDICATED // doesn't make sense on dedicated server
+	// doesn't make sense on dedicated server and SDL3 handles this in GLimp_GrabInput()
+#if !defined(ID_DEDICATED) && ! SDL_VERSION_ATLEAST(3, 0, 0)
 	if ( in_grabKeyboard.IsModified() ) {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 		SDL_SetHint( SDL_HINT_GRAB_KEYBOARD, in_grabKeyboard.GetString() );
diff --git a/neo/sys/glimp.cpp b/neo/sys/glimp.cpp
index 1f0bad2e..4bd3f52b 100644
--- a/neo/sys/glimp.cpp
+++ b/neo/sys/glimp.cpp
@@ -26,7 +26,17 @@ If you have questions concerning this license or the applicable additional terms
 ===========================================================================
 */
 
-#include <SDL.h>
+#ifdef D3_SDL3
+  #include <SDL3/SDL.h>
+  // backwards-compat with SDL2
+  #define SDL_WINDOW_ALLOW_HIGHDPI SDL_WINDOW_HIGH_PIXEL_DENSITY
+  #define SDL_GL_DeleteContext SDL_GL_DestroyContext
+  typedef SDL_WindowFlags My_SDL_WindowFlags;
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+  // for compat with SDL3 - unfortunately SDL2 also has a SDL_WindowFlags type, but it's an enum
+  typedef Uint32 My_SDL_WindowFlags;
+#endif
 
 #include "sys/platform.h"
 #include "framework/Licensee.h"
@@ -99,7 +109,6 @@ If you have questions concerning this license or the applicable additional terms
 
 #endif // _WIN32 and ID_ALLOW_TOOLS
 
-
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 static SDL_Window *window = NULL;
 static SDL_GLContext context = NULL;
@@ -109,6 +118,24 @@ static SDL_Surface *window = NULL;
 #define SDL_WINDOW_FULLSCREEN SDL_FULLSCREEN
 #endif
 
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+
+extern idCVar in_grabKeyboard;
+
+static void SetSDLIcon()
+{
+	#include "doom_icon.h" // contains the struct d3_icon
+
+	SDL_Surface* icon = SDL_CreateSurfaceFrom(d3_icon.width, d3_icon.height,
+	                                          SDL_PIXELFORMAT_RGBA32, (void*)d3_icon.pixel_data,
+	                                          d3_icon.bytes_per_pixel*d3_icon.width);
+
+	SDL_SetWindowIcon(window, icon);
+	SDL_DestroySurface(icon);
+}
+
+#else // SDL2 and SDL1.2
+
 static void SetSDLIcon()
 {
 	Uint32 rmask, gmask, bmask, amask;
@@ -141,6 +168,7 @@ static void SetSDLIcon()
 
 	SDL_FreeSurface(icon);
 }
+#endif // SDL2 and SDL1.2
 
 /*
 ===================
@@ -152,16 +180,23 @@ bool GLimp_Init(glimpParms_t parms) {
 
 	assert(SDL_WasInit(SDL_INIT_VIDEO));
 
-	Uint32 flags = SDL_WINDOW_OPENGL;
+	My_SDL_WindowFlags flags = SDL_WINDOW_OPENGL;
 
 	if (parms.fullScreen == 1)
 	{
-#if SDL_VERSION_ATLEAST(2, 0, 0)
-		if(parms.fullScreenDesktop)
-			flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
-		else
-#endif
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+		// in SDL3 windows with SDL_WINDOW_FULLSCREEN set are fullscreen-desktop by default
+		// and for exclusive fullscreen SDL_SetWindowFullscreenMode() must be called
+		// after creating the window, so only set the flag if we want fullscreen-desktop mode
+		if(parms.fullScreen && parms.fullScreenDesktop) {
 			flags |= SDL_WINDOW_FULLSCREEN;
+		}
+#elif SDL_VERSION_ATLEAST(2, 0, 0)
+		flags |= parms.fullScreenDesktop ? SDL_WINDOW_FULLSCREEN_DESKTOP : SDL_WINDOW_FULLSCREEN;
+#else // SDL1.2
+		flags |= SDL_WINDOW_FULLSCREEN;
+#endif
+
 	}
 
 	r_windowResizable.ClearModified();
@@ -190,9 +225,10 @@ bool GLimp_Init(glimpParms_t parms) {
 	 * (unless the user disables that with r_fillWindowAlphaChan 0) */
   #ifdef SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY
 	SDL_SetHint(SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY, "1");
-  #else // little hack so this works if the SDL2 version used for building is older than runtime version
+  #elif SDL_MAJOR_VERSION == 2 // little hack so this works if the SDL2 version used for building is older than runtime version
 	SDL_SetHint("SDL_VIDEO_EGL_ALLOW_TRANSPARENCY", "1");
   #endif
+	// Note: for SDL3 we use SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN below
 #endif
 
 	int colorbits = 24;
@@ -277,7 +313,7 @@ try_again:
 		SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, (multisamples > 1) ? 1 : 0);
 		SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, multisamples);
 
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+#if SDL_VERSION_ATLEAST(2, 0, 0) // SDL2 and SDL3 window creation
 
 		if ( r_glDebugContext.GetBool() ) {
 			common->Printf( "Requesting an OpenGL Debug Context (r_glDebugContext is enabled)\n" );
@@ -292,37 +328,137 @@ try_again:
 						   windowMode, parms.width, parms.height, r_mode.GetInteger());
 		}
 
-		int displayIndex = 0;
-#if SDL_VERSION_ATLEAST(2, 0, 4)
+		Uint32 selectedDisplay = 0;
+	#if SDL_VERSION_ATLEAST(2, 0, 4)
 		// try to put the window on the display the mousecursor currently is on
 		{
+		#if SDL_VERSION_ATLEAST(3, 0, 0)
+			float x, y;
+			int numDisplays = 0;
+			SDL_DisplayID* displayIDs = SDL_GetDisplays(&numDisplays);
+		#else // SDL2
+			int numDisplays = SDL_GetNumVideoDisplays();
 			int x, y;
+		#endif
+
 			SDL_GetGlobalMouseState(&x, &y);
 
-			int numDisplays = SDL_GetNumVideoDisplays();
 			common->Printf("SDL detected %d displays: \n", numDisplays);
 			bool found = false;
 			for ( int j=0; j<numDisplays; ++j ) {
+		#if SDL_VERSION_ATLEAST(3, 0, 0)
+				SDL_DisplayID displayId_x = displayIDs[j];
+		#else // SDL2
+				int displayId_x = j;
+		#endif
 				SDL_Rect rect;
-				if (SDL_GetDisplayBounds(j, &rect) == 0) {
+				if (SDL_GetDisplayBounds(displayId_x, &rect) == 0) {
 					common->Printf(" %d: %dx%d at (%d, %d) to (%d, %d)\n", j, rect.w, rect.h,
 					               rect.x, rect.y, rect.x+rect.w, rect.y+rect.h);
 					if ( !found && x >= rect.x && x < rect.x + rect.w
 						&& y >= rect.y && y < rect.y + rect.h )
 					{
-						displayIndex = j;
+						selectedDisplay = j;
 						found = true;
 					}
 				}
 			}
-			common->Printf("Will use display %d because mouse cursor is at (%d, %d).\n",
-			               displayIndex, x, y);
+		#if SDL_VERSION_ATLEAST(3, 0, 0)
+			if(displayIDs != NULL) {
+				SDL_DisplayID displayID = displayIDs[selectedDisplay];
+				common->Printf("Will use display %u (%u) because mouse cursor is at (%g, %g).\n",
+				               selectedDisplay, displayID, x, y);
+				selectedDisplay = displayID;
+				SDL_free(displayIDs);
+			}
+		#else // SDL2
+			common->Printf("Will use display %u because mouse cursor is at (%d, %d).\n",
+			               selectedDisplay, x, y);
+		#endif
 		}
-#endif
+	#endif // SDL_VERSION_ATLEAST(2, 0, 4)
 
+	#if SDL_VERSION_ATLEAST(3, 0, 0)
+		SDL_PropertiesID props = SDL_CreateProperties();
+		SDL_SetStringProperty(props, SDL_PROP_WINDOW_CREATE_TITLE_STRING, ENGINE_VERSION);
+		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_X_NUMBER, SDL_WINDOWPOS_UNDEFINED_DISPLAY(selectedDisplay));
+		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_Y_NUMBER, SDL_WINDOWPOS_UNDEFINED_DISPLAY(selectedDisplay));
+		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_WIDTH_NUMBER, parms.width);
+		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_HEIGHT_NUMBER, parms.height);
+		SDL_SetNumberProperty(props, SDL_PROP_WINDOW_CREATE_FLAGS_NUMBER, flags);
+		// TODO: the following is probably redundant with the flag already set
+		//if ( parms.fullScreen && parms.fullScreenDesktop ) {
+		//	SDL_SetBooleanProperty(props, SDL_PROP_WINDOW_CREATE_FULLSCREEN_BOOLEAN, true);
+		//} // for exclusive fullscreen, create in windowed mode first, need to call
+
+		// TODO: SDL_SetBooleanProperty(props, SDL_PROP_WINDOW_CREATE_TRANSPARENT_BOOLEAN, true);
+		//       as replacement for SDL_VIDEO_EGL_ALLOW_TRANSPARENCY - but when?
+		//       I don't want this on all platforms.. but can I already detect wayland at this point?
+		//   Also: recent mesa versions should have this fixed, so maybe ignore the issue for SDL3? what about nvidia?
+
+		window = SDL_CreateWindowWithProperties(props);
+		SDL_DestroyProperties(props);
+		if (window == NULL) {
+			common->Warning("Couldn't set GL mode %d/%d/%d with %dx MSAA: %s",
+							channelcolorbits, tdepthbits, tstencilbits, parms.multiSamples, SDL_GetError());
+
+			// before trying to reduce color channel size or whatever, first try reducing MSAA, if possible
+			if (multisamples > 1) {
+				multisamples = (multisamples <= 2) ? 0 : (multisamples/2);
+
+				// using goto because enhancing that logic which reduces attributes
+				// based on i (so it'd first try reducing MSAA) would be too painful
+				goto try_again;
+			}
+
+			continue;
+		} else {
+			// creating the window succeeded, so adjust r_multiSamples to the value that was actually used
+			parms.multiSamples = multisamples;
+			r_multiSamples.SetInteger(multisamples);
+		}
+
+		// handle exclusive fullscreen mode
+		// TODO: just call GLimp_SetScreenParms() ?
+		if (parms.fullScreen && !parms.fullScreenDesktop) {
+			SDL_DisplayID displayID = SDL_GetDisplayForWindow( window );
+			SDL_DisplayMode mode = {};
+			if ( SDL_GetClosestFullscreenDisplayMode(displayID, parms.width, parms.height,
+			                                         parms.displayHz, true, &mode) )
+			{
+				if ( ! SDL_SetWindowFullscreenMode(window, &mode) ) {
+					common->Warning("Can't set window fullscreen mode: %s\n", SDL_GetError());
+					SDL_DestroyWindow(window);
+					window = NULL;
+					return false; // trying other color depth etc is unlikely to help with this issue
+				}
+
+				if ( ! SDL_SetWindowFullscreen(window, true) ) {
+					common->Warning("Can't switch window to fullscreen mode: %s\n", SDL_GetError());
+					SDL_DestroyWindow(window);
+					window = NULL;
+					return false; // trying other color depth etc is unlikely to help with this issue
+				}
+
+				if ( ! SDL_SyncWindow(window) ) {
+					common->Warning("SDL_SyncWindow() failed: %s\n", SDL_GetError());
+					SDL_DestroyWindow(window);
+					window = NULL;
+					return false; // trying other color depth etc is unlikely to help with this issue
+				}
+
+			} else {
+				common->Warning("Can't get display mode: %s\n", SDL_GetError());
+				SDL_DestroyWindow(window);
+				window = NULL;
+				return false; // trying other color depth etc is unlikely to help with this issue
+			}
+		}
+
+	#else // SDL2
 		window = SDL_CreateWindow(ENGINE_VERSION,
-									SDL_WINDOWPOS_UNDEFINED_DISPLAY(displayIndex),
-									SDL_WINDOWPOS_UNDEFINED_DISPLAY(displayIndex),
+									SDL_WINDOWPOS_UNDEFINED_DISPLAY(selectedDisplay),
+									SDL_WINDOWPOS_UNDEFINED_DISPLAY(selectedDisplay),
 									parms.width, parms.height, flags);
 
 		if (!window) {
@@ -364,8 +500,8 @@ try_again:
 				common->Warning("Current display mode isn't requested display mode\n");
 				common->Warning("Likely SDL bug #4700, trying to work around it..\n");
 				int dIdx = SDL_GetWindowDisplayIndex(window);
-				if(dIdx != displayIndex) {
-					common->Warning("Window's display index is %d, but we wanted %d!\n", dIdx, displayIndex);
+				if(dIdx != selectedDisplay) {
+					common->Warning("Window's display index is %d, but we wanted %d!\n", dIdx, selectedDisplay);
 				}
 
 				/* Mkay, try to hack around that. */
@@ -413,6 +549,7 @@ try_again:
 				common->Warning("Now we have the requested resolution (%d x %d)\n", parms.width, parms.height);
 			}
 		}
+	#endif // SDL2
 
 		context = SDL_GL_CreateContext(window);
 
@@ -424,7 +561,8 @@ try_again:
 
 		SetSDLIcon(); // for SDL2  this must be done after creating the window
 
-		glConfig.isFullscreen = (SDL_GetWindowFlags(window) & SDL_WINDOW_FULLSCREEN) == SDL_WINDOW_FULLSCREEN;
+		// TODO: also check for fullscreen-desktop?
+		glConfig.isFullscreen = (SDL_GetWindowFlags(window) & SDL_WINDOW_FULLSCREEN) != 0;
 		const char* fsStr = glConfig.isFullscreen ? "fullscreen " : "";
 		if ( (int)glConfig.winWidth != glConfig.vidWidth ) {
 			common->Printf( "Got a HighDPI %swindow with physical resolution %d x %d and virtual resolution %g x %g\n",
@@ -432,7 +570,7 @@ try_again:
 		} else {
 			common->Printf( "Got a %swindow with resolution %g x %g\n", fsStr, glConfig.winWidth, glConfig.winHeight );
 		}
-#else
+#else // SDL1.2 window creation
 		SDL_WM_SetCaption(ENGINE_VERSION, ENGINE_VERSION);
 
 		SetSDLIcon(); // for SDL1.2  this must be done before creating the window
@@ -654,6 +792,9 @@ bool GLimp_SetScreenParms(glimpParms_t parms) {
 		}
 		SDL_RestoreWindow( window ); // make sure we're not maximized, then setting the size wouldn't work
 		SDL_SetWindowSize( window, parms.width, parms.height );
+  #if SDL_VERSION_ATLEAST(3, 0, 0)
+		SDL_SyncWindow( window );
+  #endif
 	} else { // we want some kind of fullscreen mode
 
 		// it's probably safest to first switch to windowed mode
@@ -661,6 +802,60 @@ bool GLimp_SetScreenParms(glimpParms_t parms) {
 			SDL_SetWindowFullscreen( window, 0 );
 		}
 
+	#if SDL_VERSION_ATLEAST(3, 0, 0)
+		if ( wantFullscreenDesktop ) {
+			SDL_SetWindowFullscreenMode( window, NULL ); // setting it to NULL enables fullscreen desktop mode
+			SDL_SetWindowFullscreen( window, true );
+			// TODO: check return values
+
+			if ( ! SDL_SyncWindow( window ) ) {
+				common->Warning( "SDL_SyncWindow() failed: %s\n", SDL_GetError() );
+				//TODO: probably not SDL_DestroyWindow( window );
+				//window = NULL;
+				return false;
+			}
+		} else { // want real fullscreen
+			SDL_DisplayID displayID = SDL_GetDisplayForWindow( window );
+			SDL_DisplayMode mode = {};
+			if ( SDL_GetClosestFullscreenDisplayMode( displayID, parms.width, parms.height,
+			                                         parms.displayHz, true, &mode ) )
+			{
+				if ( ! SDL_SetWindowFullscreenMode( window, &mode ) ) {
+					common->Warning( "Can't set window fullscreen mode: %s\n", SDL_GetError() );
+					//TODO: probably not SDL_DestroyWindow( window );
+					//window = NULL;
+					return false;
+				}
+
+				if ( ! SDL_SetWindowFullscreen( window, true ) ) {
+					common->Warning( "Can't switch window to fullscreen mode: %s\n", SDL_GetError() );
+					//TODO: probably not SDL_DestroyWindow( window );
+					//window = NULL;
+					return false;
+				}
+
+				if ( ! SDL_SyncWindow( window ) ) {
+					common->Warning( "SDL_SyncWindow() failed: %s\n", SDL_GetError() );
+					//TODO: probably not SDL_DestroyWindow( window );
+					//window = NULL;
+					return false;
+				}
+
+			} else {
+				if ( parms.displayHz != 0 ) {
+					common->Warning( "Can't get display mode for %d x %d @ %dHz: %s\n", parms.width,
+					                 parms.height, parms.displayHz, SDL_GetError() );
+				} else {
+					common->Warning( "Can't get display mode for %d x %d: %s\n", parms.width,
+					                 parms.height, SDL_GetError() );
+				}
+				//TODO: probably not SDL_DestroyWindow( window );
+				//window = NULL;
+				return false;
+			}
+		}
+
+	#else // SDL2
 		if ( wantFullscreenDesktop ) {
 			if ( SDL_SetWindowFullscreen( window, SDL_WINDOW_FULLSCREEN_DESKTOP ) != 0 ) {
 				common->Warning( "GLimp_SetScreenParms(): Couldn't switch to fullscreen desktop mode, SDL error: %s\n", SDL_GetError() );
@@ -703,6 +898,7 @@ bool GLimp_SetScreenParms(glimpParms_t parms) {
 				return false;
 			}
 		}
+	#endif // SDL2
 	}
 
 	glConfig.isFullscreen = (SDL_GetWindowFlags( window ) & SDL_WINDOW_FULLSCREEN) != 0;
@@ -732,10 +928,23 @@ glimpParms_t GLimp_GetCurState()
 	}
 	ret.multiSamples = curMultiSamples;
 
-	Uint32 winFlags = SDL_GetWindowFlags( window );
+	My_SDL_WindowFlags winFlags = SDL_GetWindowFlags( window );
 	ret.fullScreen = (winFlags & SDL_WINDOW_FULLSCREEN) != 0;
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	if (ret.fullScreen) {
+		const SDL_DisplayMode* fullscreenMode = SDL_GetWindowFullscreenMode( window );
+		if (fullscreenMode != NULL) {
+			ret.width = fullscreenMode->w;
+			ret.height = fullscreenMode->h;
+			ret.displayHz = fullscreenMode->refresh_rate;
+		} else {
+			// SDL_WINDOW_FULLSCREEN is set, but SDL_GetWindowFullscreenMode() returns NULL
+			// => fullscreen desktop mode
+			ret.fullScreenDesktop = true;
+		}
+	}
+#else // SDL2
 	ret.fullScreenDesktop = (winFlags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP;
-
 	if ( ret.fullScreen && !ret.fullScreenDesktop ) { // I think SDL_GetWindowDisplayMode() is only for "real" fullscreen?
 		SDL_DisplayMode real_mode = {};
 		if ( SDL_GetWindowDisplayMode( window, &real_mode ) == 0 ) {
@@ -746,7 +955,9 @@ glimpParms_t GLimp_GetCurState()
 			common->Warning( "GLimp_GetCurState(): Can't get display mode: %s\n", SDL_GetError() );
 		}
 	}
-	if ( ret.width == 0 && ret.height == 0 ) { // windowed mode or SDL_GetWindowDisplayMode() failed
+#endif
+
+	if ( ret.width == 0 && ret.height == 0 ) { // windowed mode, fullscreen-desktop mode or SDL_GetWindowDisplayMode() failed
 		SDL_GetWindowSize( window, &ret.width, &ret.height );
 	}
 
@@ -797,11 +1008,14 @@ void GLimp_SwapBuffers() {
 #endif
 }
 
+// SDL3 doesn't support hardware gamma
+#if ! SDL_VERSION_ATLEAST(3, 0, 0)
 static bool gammaOrigError = false;
 static bool gammaOrigSet = false;
 static unsigned short gammaOrigRed[256];
 static unsigned short gammaOrigGreen[256];
 static unsigned short gammaOrigBlue[256];
+#endif
 
 /*
 =================
@@ -809,6 +1023,12 @@ GLimp_SetGamma
 =================
 */
 void GLimp_SetGamma(unsigned short red[256], unsigned short green[256], unsigned short blue[256]) {
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	if ( ! r_gammaInShader.GetBool() ) {
+		common->Warning( "This build of dhewm3 uses SDL3, which does not support hardware gamma." );
+		common->Warning( "If you want to adjust gamma or brightness, enable r_gammaInShader" );
+	}
+#else // SDL2 and SDL1.2
 	if (!window) {
 		common->Warning("GLimp_SetGamma called without window");
 		return;
@@ -833,6 +1053,7 @@ void GLimp_SetGamma(unsigned short red[256], unsigned short green[256], unsigned
 	if (SDL_SetGammaRamp(red, green, blue))
 #endif
 		common->Warning("Couldn't set gamma ramp: %s", SDL_GetError());
+#endif // SDL2 and SDL1.2
 }
 
 /*
@@ -843,6 +1064,7 @@ Restore original system gamma setting
 =================
 */
 void GLimp_ResetGamma() {
+#if ! SDL_VERSION_ATLEAST(3, 0, 0) // only for SDL2 and SDL1.2
 	if( gammaOrigError ) {
 		common->Warning( "Can't reset hardware gamma because getting the Gamma Ramp at startup failed!\n" );
 		common->Warning( "You might have to restart the game for gamma/brightness in shaders to work properly.\n" );
@@ -850,12 +1072,13 @@ void GLimp_ResetGamma() {
 	}
 
 	if( gammaOrigSet ) {
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+  #if SDL_VERSION_ATLEAST(2, 0, 0)
 		SDL_SetWindowGammaRamp( window, gammaOrigRed, gammaOrigGreen, gammaOrigBlue );
-#else
+  #else
 		SDL_SetGammaRamp( gammaOrigRed, gammaOrigGreen, gammaOrigBlue );
-#endif
+  #endif
 	}
+#endif // ! SDL_VERSION_ATLEAST(3, 0, 0)
 }
 
 
@@ -893,8 +1116,21 @@ void GLimp_GrabInput(int flags) {
 		common->Warning("GLimp_GrabInput called without window");
 		return;
 	}
-
-#if SDL_VERSION_ATLEAST(2, 0, 0)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	if (flags & GRAB_HIDECURSOR) {
+		SDL_HideCursor();
+	} else {
+		SDL_ShowCursor();
+	}
+	SDL_SetWindowRelativeMouseMode( window, (flags & GRAB_RELATIVEMOUSE) != 0 );
+	if (flags & GRAB_GRABMOUSE) {
+		SDL_SetWindowMouseGrab( window, true );
+		SDL_SetWindowKeyboardGrab( window, in_grabKeyboard.GetBool() );
+	} else {
+		SDL_SetWindowMouseGrab( window, false );
+		SDL_SetWindowKeyboardGrab( window, false );
+	}
+#elif SDL_VERSION_ATLEAST(2, 0, 0)
 	SDL_ShowCursor( (flags & GRAB_HIDECURSOR) ? SDL_DISABLE : SDL_ENABLE );
 	SDL_SetRelativeMouseMode( (flags & GRAB_RELATIVEMOUSE) ? SDL_TRUE : SDL_FALSE );
 	SDL_SetWindowGrab( window, (flags & GRAB_GRABMOUSE) ? SDL_TRUE : SDL_FALSE );
@@ -909,7 +1145,11 @@ void GLimp_GrabInput(int flags) {
 bool GLimp_SetSwapInterval( int swapInterval )
 {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
+  #if SDL_VERSION_ATLEAST(3, 0, 0)
+	if ( ! SDL_GL_SetSwapInterval( swapInterval ) ) {
+  #elif SDL_VERSION_ATLEAST(2, 0, 0)
 	if ( SDL_GL_SetSwapInterval( swapInterval ) < 0 ) {
+  #endif
 		common->Warning( "SDL_GL_SetSwapInterval( %d ) not supported", swapInterval );
 		return false;
 	}
@@ -922,7 +1162,10 @@ bool GLimp_SetSwapInterval( int swapInterval )
 
 bool GLimp_SetWindowResizable( bool enableResizable )
 {
-#if SDL_VERSION_ATLEAST(2, 0, 5)
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	SDL_SetWindowResizable( window, enableResizable );
+	return true;
+#elif SDL_VERSION_ATLEAST(2, 0, 5)
 	SDL_SetWindowResizable( window, (SDL_bool)enableResizable );
 	return true;
 #else
@@ -934,7 +1177,18 @@ bool GLimp_SetWindowResizable( bool enableResizable )
 void GLimp_UpdateWindowSize()
 {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	Uint32 winFlags = SDL_GetWindowFlags( window );
+	My_SDL_WindowFlags winFlags = SDL_GetWindowFlags( window );
+
+  #if SDL_VERSION_ATLEAST(3, 0, 0)
+	SDL_GetWindowSizeInPixels( window, &glConfig.vidWidth, &glConfig.vidHeight );
+
+	const SDL_DisplayMode* fullscreenMode = SDL_GetWindowFullscreenMode( window );
+	if ( (winFlags & SDL_WINDOW_FULLSCREEN) != 0 && fullscreenMode != NULL) {
+		glConfig.winWidth = fullscreenMode->w;
+		glConfig.winHeight = fullscreenMode->h;
+	}
+  #else // SDL2
+	SDL_GL_GetDrawableSize( window, &glConfig.vidWidth, &glConfig.vidHeight );
 	if ( (winFlags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN ) {
 		// real fullscreen mode => must use SDL_GetWindowDisplayMode()
 		// TODO: well, theoretically SDL_GetWindowSize() should work for fullscreen mode as well,
@@ -951,13 +1205,13 @@ void GLimp_UpdateWindowSize()
 		} else {
 			common->Warning( "GLimp_UpdateWindowSize(): SDL_GetWindowDisplayMode() failed: %s\n", SDL_GetError() );
 		}
-
-	} else {
+	}
+  #endif // SDL2
+	  else {
 		int ww=0, wh=0;
 		SDL_GetWindowSize( window, &ww, &wh );
 		glConfig.winWidth = ww;
 		glConfig.winHeight = wh;
 	}
-	SDL_GL_GetDrawableSize( window, &glConfig.vidWidth, &glConfig.vidHeight );
 #endif
 }
diff --git a/neo/sys/linux/main.cpp b/neo/sys/linux/main.cpp
index 28a8a9b5..3468d393 100644
--- a/neo/sys/linux/main.cpp
+++ b/neo/sys/linux/main.cpp
@@ -32,7 +32,7 @@ If you have questions concerning this license or the applicable additional terms
 #include <sys/types.h>
 #include <fcntl.h>
 
-#include <SDL_main.h>
+//#include <SDL_main.h> - not needed, dhewm3 doesn't currently use SDL's SDL_main
 
 #include "sys/platform.h"
 #include "framework/Licensee.h"
diff --git a/neo/sys/posix/posix_main.cpp b/neo/sys/posix/posix_main.cpp
index ee975d32..276a0bb9 100644
--- a/neo/sys/posix/posix_main.cpp
+++ b/neo/sys/posix/posix_main.cpp
@@ -49,7 +49,13 @@ If you have questions concerning this license or the applicable additional terms
 
 #include "sys/posix/posix_public.h"
 
-#include <SDL.h> // clipboard
+// SDL.h for clipboard:
+#ifdef D3_SDL3
+  #include <SDL3/SDL.h>
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+#endif
+
 
 #define					COMMAND_HISTORY 64
 
diff --git a/neo/sys/sys_imgui.cpp b/neo/sys/sys_imgui.cpp
index 0a3003de..435d181d 100644
--- a/neo/sys/sys_imgui.cpp
+++ b/neo/sys/sys_imgui.cpp
@@ -1,7 +1,20 @@
 
 #define IMGUI_DEFINE_MATH_OPERATORS
 
-#include <SDL.h>
+#ifdef D3_SDL3
+  #include <SDL3/SDL.h>
+  // compat with SDL2
+  #define SDL_TEXTINPUT SDL_EVENT_TEXT_INPUT
+  #define SDL_CONTROLLERAXISMOTION SDL_EVENT_GAMEPAD_AXIS_MOTION
+  #define SDL_CONTROLLERBUTTONDOWN SDL_EVENT_GAMEPAD_BUTTON_DOWN
+  #define SDL_MOUSEBUTTONDOWN SDL_EVENT_MOUSE_BUTTON_DOWN
+  #define SDL_MOUSEMOTION SDL_EVENT_MOUSE_MOTION
+  #define SDL_MOUSEWHEEL SDL_EVENT_MOUSE_WHEEL
+  #define SDL_KEYDOWN SDL_EVENT_KEY_DOWN
+#else // SDL2
+  #include <SDL.h>
+#endif
+
 
 #include "sys_imgui.h"
 
@@ -13,7 +26,20 @@ typedef char* (*MY_XGETDEFAULTFUN)(Display*, const char*, const char*);
 #endif
 
 #include "../libs/imgui/backends/imgui_impl_opengl2.h"
-#include "../libs/imgui/backends/imgui_impl_sdl2.h"
+
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+  #include "../libs/imgui/backends/imgui_impl_sdl3.h"
+  #define ImGui_ImplSDLx_InitForOpenGL ImGui_ImplSDL3_InitForOpenGL
+  #define ImGui_ImplSDLx_Shutdown ImGui_ImplSDL3_Shutdown
+  #define ImGui_ImplSDLx_NewFrame ImGui_ImplSDL3_NewFrame
+  #define ImGui_ImplSDLx_ProcessEvent ImGui_ImplSDL3_ProcessEvent
+#else
+  #include "../libs/imgui/backends/imgui_impl_sdl2.h"
+  #define ImGui_ImplSDLx_InitForOpenGL ImGui_ImplSDL2_InitForOpenGL
+  #define ImGui_ImplSDLx_Shutdown ImGui_ImplSDL2_Shutdown
+  #define ImGui_ImplSDLx_NewFrame ImGui_ImplSDL2_NewFrame
+  #define ImGui_ImplSDLx_ProcessEvent ImGui_ImplSDL2_ProcessEvent
+#endif
 
 #include "framework/Common.h"
 #include "framework/KeyInput.h"
@@ -145,7 +171,7 @@ void ShowWarningOverlay( const char* text )
 	warningOverlayStartPos = ImGui::GetMousePos();
 }
 
-
+#if SDL_MAJOR_VERSION == 2 // not used with SDL3
 static float GetDefaultDPI()
 {
 	SDL_Window* win = sdlWindow;
@@ -185,6 +211,7 @@ static float GetDefaultDPI()
 	}
 	return dpi;
 }
+#endif // SDL2-only
 
 static float GetDefaultScale()
 {
@@ -192,8 +219,13 @@ static float GetDefaultScale()
 		// in HighDPI mode, the font sizes are already scaled (to window coordinates), apparently
 		return 1.0f;
 	}
+
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	float ret = SDL_GetWindowDisplayScale( sdlWindow );
+#else
 	// TODO: different reference DPI on mac? also, doesn't work that well on my laptop..
 	float ret = GetDefaultDPI() / 96.0f;
+#endif
 	ret = round(ret*2.0)*0.5; // round to .0 or .5
 	return ret;
 }
@@ -250,7 +282,7 @@ bool Init(void* _sdlWindow, void* sdlGlContext)
 	imgui_scale.SetModified(); // so NewFrame() will load the scaled font
 
 	// Setup Platform/Renderer backends
-	if ( ! ImGui_ImplSDL2_InitForOpenGL( sdlWindow, sdlGlContext ) ) {
+	if ( ! ImGui_ImplSDLx_InitForOpenGL( sdlWindow, sdlGlContext ) ) {
 		ImGui::DestroyContext( imguiCtx );
 		imguiCtx = NULL;
 		common->Warning( "Failed to initialize ImGui SDL platform backend!\n" );
@@ -258,7 +290,7 @@ bool Init(void* _sdlWindow, void* sdlGlContext)
 	}
 
 	if ( ! ImGui_ImplOpenGL2_Init() ) {
-		ImGui_ImplSDL2_Shutdown();
+		ImGui_ImplSDLx_Shutdown();
 		ImGui::DestroyContext( imguiCtx );
 		imguiCtx = NULL;
 		common->Warning( "Failed to initialize ImGui OpenGL renderer backend!\n" );
@@ -302,7 +334,7 @@ void Shutdown()
 
 		// TODO: only if init was successful!
 		ImGui_ImplOpenGL2_Shutdown();
-		ImGui_ImplSDL2_Shutdown();
+		ImGui_ImplSDLx_Shutdown();
 		ImGui::DestroyContext( imguiCtx );
 		imgui_initialized = false;
 	}
@@ -345,7 +377,7 @@ void NewFrame()
 	else
 		ImGui::GetIO().ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange;
 
-	ImGui_ImplSDL2_NewFrame();
+	ImGui_ImplSDLx_NewFrame();
 	ImGui::NewFrame();
 	haveNewFrame = true;
 
@@ -379,7 +411,7 @@ bool ProcessEvent(const void* sdlEvent)
 	//   - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
 	//   Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
 
-	bool imguiUsedEvent = ImGui_ImplSDL2_ProcessEvent( ev );
+	bool imguiUsedEvent = ImGui_ImplSDLx_ProcessEvent( ev );
 	if ( keybindModeEnabled ) {
 		// in keybind mode, all input events are passed to Doom3 so it can translate them
 		// to internal events and we can access and use them to create a new binding
@@ -424,7 +456,11 @@ bool ProcessEvent(const void* sdlEvent)
 					return true;
 				case SDL_KEYDOWN:
 				//case SDL_KEYUP: NOTE: see above why key up events are passed to the engine
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+					if ( ev->key.key < SDLK_F1 || ev->key.key > SDLK_F12) {
+#else
 					if ( ev->key.keysym.sym < SDLK_F1 || ev->key.keysym.sym > SDLK_F12) {
+#endif
 						// F1 - F12 are passed to the engine so its shortcuts
 						// (like quickload or screenshot) still work
 						// Doom3's menu does the same
diff --git a/neo/sys/threads.cpp b/neo/sys/threads.cpp
index 0b1132ae..99eb9e8c 100644
--- a/neo/sys/threads.cpp
+++ b/neo/sys/threads.cpp
@@ -26,10 +26,15 @@ If you have questions concerning this license or the applicable additional terms
 ===========================================================================
 */
 
-#include <SDL_version.h>
-#include <SDL_mutex.h>
-#include <SDL_thread.h>
-#include <SDL_timer.h>
+#ifdef D3_SDL3
+  #define SDL_oldnames_h_ // HACK: I don't want SDL.h to drag in SDL_oldnames.h to avoid all the warnings about redefined definitions
+  #include <SDL3/SDL.h>
+#else // SDL1.2 or SDL2
+  #include <SDL_version.h>
+  #include <SDL_mutex.h>
+  #include <SDL_thread.h>
+  #include <SDL_timer.h>
+#endif
 
 #include "sys/platform.h"
 #include "framework/Common.h"
@@ -40,6 +45,15 @@ If you have questions concerning this license or the applicable additional terms
   // SDL1.2 doesn't have SDL_threadID but uses Uint32.
   // this typedef helps using the same code for SDL1.2 and SDL2
   typedef Uint32 SDL_threadID;
+#elif SDL_MAJOR_VERSION >= 3
+  // backwards-compat with SDL2
+  #define SDL_mutex SDL_Mutex
+  #define SDL_cond SDL_Condition
+  #define SDL_threadID SDL_ThreadID
+  #define SDL_CreateCond SDL_CreateCondition
+  #define SDL_DestroyCond SDL_DestroyCondition
+  #define SDL_CondWait SDL_WaitCondition
+  #define SDL_CondSignal SDL_SignalCondition
 #endif
 
 #if __cplusplus >= 201103
@@ -159,8 +173,12 @@ Sys_EnterCriticalSection
 void Sys_EnterCriticalSection(int index) {
 	assert(index >= 0 && index < MAX_CRITICAL_SECTIONS);
 
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	SDL_LockMutex(mutex[index]); // in SDL3, this returns void and can't fail
+#else // SDL2 and SDL1.2
 	if (SDL_LockMutex(mutex[index]) != 0)
 		common->Error("ERROR: SDL_LockMutex failed\n");
+#endif
 }
 
 /*
@@ -171,8 +189,12 @@ Sys_LeaveCriticalSection
 void Sys_LeaveCriticalSection(int index) {
 	assert(index >= 0 && index < MAX_CRITICAL_SECTIONS);
 
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+	SDL_UnlockMutex(mutex[index]); // in SDL3, this returns void and can't fail
+#else // SDL2 and SDL1.2
 	if (SDL_UnlockMutex(mutex[index]) != 0)
 		common->Error("ERROR: SDL_UnlockMutex failed\n");
+#endif
 }
 
 /*
@@ -204,8 +226,12 @@ void Sys_WaitForEvent(int index) {
 		signaled[index] = false;
 	} else {
 		waiting[index] = true;
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+		SDL_CondWait(cond[index], mutex[CRITICAL_SECTION_SYS]); // in SDL3, this returns void and can't fail
+#else // SDL2 and SDL1.2
 		if (SDL_CondWait(cond[index], mutex[CRITICAL_SECTION_SYS]) != 0)
 			common->Error("ERROR: SDL_CondWait failed\n");
+#endif
 		waiting[index] = false;
 	}
 
@@ -223,8 +249,12 @@ void Sys_TriggerEvent(int index) {
 	Sys_EnterCriticalSection(CRITICAL_SECTION_SYS);
 
 	if (waiting[index]) {
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+		SDL_CondSignal(cond[index]); // in SDL3, this returns void and can't fail
+#else // SDL2 and SDL1.2
 		if (SDL_CondSignal(cond[index]) != 0)
 			common->Error("ERROR: SDL_CondSignal failed\n");
+#endif
 	} else {
 		// emulate windows behaviour: if no thread is waiting, leave the signal on so next wait keeps going
 		signaled[index] = true;
diff --git a/neo/tools/debugger/DebuggerServer.cpp b/neo/tools/debugger/DebuggerServer.cpp
index 3b3adc7d..5d4446d6 100644
--- a/neo/tools/debugger/DebuggerServer.cpp
+++ b/neo/tools/debugger/DebuggerServer.cpp
@@ -41,6 +41,14 @@ If you have questions concerning this license or the applicable additional terms
 const int MAX_MSGLEN = 8600;
 #endif
 
+#if SDL_VERSION_ATLEAST(3, 0, 0)
+  // compat with SDL2
+  #define SDL_CreateCond SDL_CreateCondition
+  #define SDL_DestroyCond SDL_DestroyCondition
+  #define SDL_CondWait SDL_WaitCondition
+  #define SDL_CondSignal SDL_SignalCondition
+#endif
+
 /*
 ================
 rvDebuggerServer::rvDebuggerServer
diff --git a/neo/tools/debugger/DebuggerServer.h b/neo/tools/debugger/DebuggerServer.h
index 8f741ea1..8d62a5cd 100644
--- a/neo/tools/debugger/DebuggerServer.h
+++ b/neo/tools/debugger/DebuggerServer.h
@@ -28,7 +28,16 @@ If you have questions concerning this license or the applicable additional terms
 #ifndef DEBUGGERSERVER_H_
 #define DEBUGGERSERVER_H_
 
-#include <SDL.h>
+#ifdef D3_SDL3
+  #define SDL_oldnames_h_ // HACK: I don't want SDL.h to drag in SDL_oldnames.h to avoid all the warnings about redefined definitions
+  #include <SDL3/SDL.h>
+  // backwards-compat with SDL <= 2
+  #define SDL_mutex SDL_Mutex
+  #define SDL_cond SDL_Condition
+#else // SDL1.2 or SDL2
+  #include <SDL.h>
+#endif
+
 #include "sys/platform.h"
 #include "idlib/Str.h"
 #include "DebuggerMessages.h"