Implement built-in gyroscope support for SDL2 platforms

engine/client/in_gyro.c

@@ -0,0 +1,120 @@
+/*
+in_gyro.c - System gyroscope input code
+Copyright (C) 2026 Xash3D FWGS contributors
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+*/
+
+#include "common.h"
+#include "input.h"
+#include "client.h"
+
+static CVAR_DEFINE_AUTO( gyro_enable, "0", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "enables aiming with built-in device gyroscope" );
+static CVAR_DEFINE_AUTO( gyro_available, "0", FCVAR_READ_ONLY, "tells whether system gyroscope hardware is available or not" );
+static CVAR_DEFINE_AUTO( gyro_pitch, "1.0", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope sensitivity for looking up and down" );
+static CVAR_DEFINE_AUTO( gyro_yaw, "1.0", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope sensitivity for turning left and right" );
+static CVAR_DEFINE_AUTO( gyro_roll, "0.0", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope sensitivity when tilting the device sideways" );
+static CVAR_DEFINE_AUTO( gyro_pitch_deadzone, "0.5", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope pitch axis deadzone (deg/s)" );
+static CVAR_DEFINE_AUTO( gyro_yaw_deadzone, "0.5", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope yaw axis deadzone (deg/s)" );
+static CVAR_DEFINE_AUTO( gyro_roll_deadzone, "0.5", FCVAR_ARCHIVE | FCVAR_FILTERABLE, "built-in gyroscope roll axis deadzone (deg/s)" );
+
+// stores the latest instantaneous rotation rates from built-in gyroscope
+static vec3_t gyro_speed;
+
+/*
+==============
+IN_GyroInit
+
+==============
+*/
+void IN_GyroInit( void )
+{
+	Cvar_RegisterVariable( &gyro_enable );
+	Cvar_RegisterVariable( &gyro_available );
+	Cvar_RegisterVariable( &gyro_pitch );
+	Cvar_RegisterVariable( &gyro_yaw );
+	Cvar_RegisterVariable( &gyro_roll );
+	Cvar_RegisterVariable( &gyro_pitch_deadzone );
+	Cvar_RegisterVariable( &gyro_yaw_deadzone );
+	Cvar_RegisterVariable( &gyro_roll_deadzone );
+}
+
+/*
+==============
+IN_GyroCheckAvailability
+
+One-time late check called after startup and configs
+==============
+*/
+void IN_GyroCheckAvailability( void )
+{
+#if XASH_SDL
+	if( gyro_available.value )
+		return;
+
+	if( SDLash_GyroIsAvailable() )
+	{
+		Cvar_FullSet( "gyro_available", "1", FCVAR_READ_ONLY );
+	}
+#endif
+}
+
+/*
+=============
+IN_GyroEvent
+
+System gyroscope events from platform
+=============
+*/
+void IN_GyroEvent( vec3_t data )
+{
+	VectorCopy( data, gyro_speed );
+}
+
+/*
+=============
+IN_GyroFinalizeMove
+
+Apply gyro movement to view angles
+=============
+*/
+void IN_GyroFinalizeMove( float *fw, float *side, float *dpitch, float *dyaw )
+{
+	platform_orientation_t orient;
+	float orient_scale = 1.0f;
+
+	if( !gyro_enable.value || !gyro_available.value )
+		return;
+
+	orient = Platform_GetDisplayOrientation();
+	if( orient == ORIENTATION_LANDSCAPE_FLIPPED )
+		orient_scale = -1.0f;
+
+	// In Landscape mode axes are swapped relative to natural (Portrait) orientation
+	// Y axis rotation becomes Pitch (up/down)
+	// X axis rotation becomes Yaw (left/right)
+	float pitch_speed = -orient_scale * gyro_speed[1] * ( 180.0f / M_PI );
+	float yaw_speed   = -orient_scale * gyro_speed[0] * ( 180.0f / M_PI );
+	float roll_speed  = orient_scale * gyro_speed[2] * ( 180.0f / M_PI );
+
+	if( fabs( pitch_speed ) < gyro_pitch_deadzone.value )
+		pitch_speed = 0.0f;
+	if( fabs( yaw_speed ) < gyro_yaw_deadzone.value )
+		yaw_speed = 0.0f;
+	if( fabs( roll_speed ) < gyro_roll_deadzone.value )
+		roll_speed = 0.0f;
+
+	*dpitch -= gyro_pitch.value * pitch_speed * host.realframetime;
+	*dyaw   += gyro_yaw.value   * yaw_speed   * host.realframetime;
+	*dyaw   += gyro_roll.value  * roll_speed  * host.realframetime;
+
+	VectorClear( gyro_speed );
+}

engine/client/input.c

@@ -445,6 +445,8 @@ void IN_Init( void )
 	{
 		IN_StartupMouse( );
 
+		IN_GyroInit();
+
 		Joy_Init(); // common joystick support init
 
 		Touch_Init();
@@ -560,6 +562,7 @@ static void IN_CollectInput( float *forward, float *side, float *pitch, float *y
 #endif
 	}
 
+	IN_GyroFinalizeMove( forward, side, pitch, yaw );
 	Joy_FinalizeMove( forward, side, pitch, yaw );
 	Touch_GetMove( forward, side, pitch, yaw );
 

engine/client/input.h

@@ -39,6 +39,10 @@ void IN_DeactivateMouse( void );
 void IN_MouseSavePos( void );
 void IN_MouseRestorePos( void );
 void IN_ToggleClientMouse( int newstate, int oldstate );
+void IN_GyroInit( void );
+void IN_GyroCheckAvailability( void );
+void IN_GyroEvent( vec3_t data );
+void IN_GyroFinalizeMove( float *fw, float *side, float *dpitch, float *dyaw );
 
 uint IN_CollectInputDevices( void );
 void IN_LockInputDevices( qboolean lock );

engine/common/host.c

@@ -1276,6 +1276,10 @@ int EXPORT Host_Main( int argc, char **argv, const char *progname, int bChangeGa
 	Cbuf_ExecStuffCmds();	// execute stuffcmds (commandline)
 	SCR_CheckStartupVids();	// must be last
 
+#ifndef XASH_DEDICATED
+	IN_GyroCheckAvailability();
+#endif
+
 	if( Sys_GetParmFromCmdLine( "-timedemo", demoname ))
 		Cbuf_AddTextf( "timedemo %s\n", demoname );
 

engine/platform/platform.h

@@ -40,6 +40,17 @@ void Platform_MessageBox( const char *title, const char *message, qboolean paren
 void Platform_SetStatus( const char *status );
 qboolean Platform_DebuggerPresent( void );
 
+typedef enum
+{
+	ORIENTATION_UNKNOWN = 0,
+	ORIENTATION_LANDSCAPE,
+	ORIENTATION_LANDSCAPE_FLIPPED,
+	ORIENTATION_PORTRAIT,
+	ORIENTATION_PORTRAIT_FLIPPED
+} platform_orientation_t;
+
+platform_orientation_t Platform_GetDisplayOrientation( void );
+
 // legacy iOS port functions
 #if XASH_IOS
 int IOS_GetArgs( char ***argv );
@@ -64,6 +75,7 @@ char *Posix_Input( void );
 void SDLash_Init( void );
 void SDLash_Shutdown( void );
 void SDLash_NanoSleep( int nsec );
+qboolean SDLash_GyroIsAvailable( void );
 #endif
 
 #if XASH_ANDROID

engine/platform/sdl2/host_sdl2.c

@@ -368,6 +368,11 @@ static void SDLash_EventHandler( SDL_Event *event )
 #endif
 		SDLash_HandleGameControllerEvent( event );
 		break;
+#if SDL_VERSION_ATLEAST( 2, 0, 14 )
+	case SDL_SENSORUPDATE:
+		SDLash_SensorUpdate( event->sensor );
+		break;
+#endif
 
 	case SDL_WINDOWEVENT:
 		if( event->window.windowID != SDL_GetWindowID( host.hWnd ) )

engine/platform/sdl2/platform_sdl2.h

@@ -35,5 +35,15 @@ void SDLash_FreeCursors( void );
 //
 void SDLash_HandleGameControllerEvent( SDL_Event *ev );
 
+//
+// sensor_sdl2.c
+//
+void SDLash_InitSensors( void );
+void SDLash_ShutdownSensors( void );
+qboolean SDLash_GyroIsAvailable( void );
+#if SDL_VERSION_ATLEAST( 2, 0, 14 )
+void SDLash_SensorUpdate( SDL_SensorEvent sensor );
+#endif
+
 #endif // XASH_SDL
 #endif // KEYWRAPPER_H

engine/platform/sdl2/sensor_sdl2.c

@@ -0,0 +1,103 @@
+/*
+sensor_sdl2.c - SDL2 sensor handling
+Copyright (C) 2026 Xash3D FWGS contributors
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+*/
+
+#include <SDL.h>
+#include "common.h"
+#include "input.h"
+#include "platform_sdl2.h"
+
+#if SDL_VERSION_ATLEAST( 2, 0, 14 )
+static SDL_SensorID g_system_gyro_id = -1;
+static SDL_Sensor *g_system_gyro;
+
+/*
+==============
+SDLash_InitSensors
+
+==============
+*/
+void SDLash_InitSensors( void )
+{
+	if( SDL_InitSubSystem( SDL_INIT_SENSOR ) == 0 )
+	{
+		int num_sensors = SDL_NumSensors();
+
+		for( int i = 0; i < num_sensors; i++ )
+		{
+			if( SDL_SensorGetDeviceType( i ) == SDL_SENSOR_GYRO )
+			{
+				g_system_gyro = SDL_SensorOpen( i );
+				if( g_system_gyro )
+				{
+					g_system_gyro_id = SDL_SensorGetInstanceID( g_system_gyro );
+					Con_Printf( "SDL: Opened built-in gyroscope: %s\n", SDL_SensorGetName( g_system_gyro ) );
+					break;
+				}
+			}
+		}
+	}
+	else
+	{
+		Con_Reportf( S_ERROR "Failed to init SDL Sensor subsystem: %s\n", SDL_GetError() );
+	}
+}
+
+/*
+==============
+SDLash_ShutdownSensors
+
+==============
+*/
+void SDLash_ShutdownSensors( void )
+{
+	if( g_system_gyro )
+	{
+		SDL_SensorClose( g_system_gyro );
+		g_system_gyro = NULL;
+		g_system_gyro_id = -1;
+	}
+
+	SDL_QuitSubSystem( SDL_INIT_SENSOR );
+}
+
+/*
+==============
+SDLash_GyroIsAvailable
+
+==============
+*/
+qboolean SDLash_GyroIsAvailable( void )
+{
+	return ( g_system_gyro != NULL );
+}
+
+/*
+==============
+SDLash_SensorUpdate
+
+==============
+*/
+void SDLash_SensorUpdate( SDL_SensorEvent sensor )
+{
+	if( sensor.which == g_system_gyro_id )
+	{
+		IN_GyroEvent( sensor.data );
+	}
+}
+#else
+void SDLash_InitSensors( void ) { }
+void SDLash_ShutdownSensors( void ) { }
+qboolean SDLash_GyroIsAvailable( void ) { return false; }
+#endif

engine/platform/sdl2/sys_sdl2.c

@@ -146,10 +146,12 @@ void SDLash_Init( void )
 	SDL_StopTextInput();
 
 	SDLash_InitCursors();
+	SDLash_InitSensors();
 }
 
 void SDLash_Shutdown( void )
 {
+	SDLash_ShutdownSensors();
 	SDLash_FreeCursors();
 
 	SDL_Quit();

engine/platform/sdl2/vid_sdl2.c

@@ -1204,3 +1204,29 @@ void VID_Info_f( void )
 	else
 		Con_Printf( "Window display mode: " S_RED "fail: " S_DEFAULT "%s\n", SDL_GetError( ));
 }
+
+platform_orientation_t Platform_GetDisplayOrientation( void )
+{
+	if( host.hWnd )
+	{
+		int display_index = SDL_GetWindowDisplayIndex( host.hWnd );
+		if( display_index >= 0 )
+		{
+			switch( SDL_GetDisplayOrientation( display_index ) )
+			{
+			case SDL_ORIENTATION_LANDSCAPE:
+				return ORIENTATION_LANDSCAPE;
+			case SDL_ORIENTATION_LANDSCAPE_FLIPPED:
+				return ORIENTATION_LANDSCAPE_FLIPPED;
+			case SDL_ORIENTATION_PORTRAIT:
+				return ORIENTATION_PORTRAIT;
+			case SDL_ORIENTATION_PORTRAIT_FLIPPED:
+				return ORIENTATION_PORTRAIT_FLIPPED;
+			default:
+				return ORIENTATION_UNKNOWN;
+			}
+		}
+	}
+
+	return ORIENTATION_UNKNOWN;
+}