From ffa53f14e55d998f9706422c87b8b0989a347c5f Mon Sep 17 00:00:00 2001
From: Alibek Omarov <a1ba.omarov@gmail.com>
Date: Wed, 8 Apr 2026 11:31:01 +0500
Subject: [PATCH] engine: platform: sdl2: implement continuous background
 recalibration for gyroscope

---
 engine/platform/sdl2/joy_sdl2.c | 80 ++++++++++++++++++++++++---------
 1 file changed, 58 insertions(+), 22 deletions(-)

diff --git a/engine/platform/sdl2/joy_sdl2.c b/engine/platform/sdl2/joy_sdl2.c
index 99e47aa7..d7f4945d 100644
--- a/engine/platform/sdl2/joy_sdl2.c
+++ b/engine/platform/sdl2/joy_sdl2.c
@@ -52,15 +52,16 @@ static SDL_GameController *g_current_gamepad;
 static SDL_GameController **g_gamepads;
 static size_t g_num_gamepads;
 
-#define CALIBRATION_TIME 10.0f
+#define CALIBRATION_TIME 5.0f
 
 static struct
 {
-	float  time;
-	vec3_t data;
-	vec3_t calibrated_values;
-	float  data_rate;
-	int    samples;
+	float    time;
+	vec3_t   data;
+	vec3_t   calibrated_values;
+	float    data_rate;
+	int      samples;
+	qboolean continuous; // true after first successful calibration
 } gyrocal;
 
 static void SDLash_RestartCalibration( void )
@@ -77,7 +78,7 @@ static void SDLash_RestartCalibration( void )
 	if( !gyrocal.data_rate )
 		gyrocal.data_rate = 10.0f;
 
-	Con_Printf( "Starting gyroscope calibration at %g data rate...\n", gyrocal.data_rate );
+	Con_Printf( S_NOTE "Starting gyroscope calibration at %g data rate for %g seconds...\n", gyrocal.data_rate, CALIBRATION_TIME );
 }
 
 static void SDLash_FinalizeCalibration( void )
@@ -87,14 +88,53 @@ static void SDLash_FinalizeCalibration( void )
 	// we waited for few seconds and got too few samples
 	if( gyrocal.samples <= min_samples )
 	{
-		Joy_SetCalibrationState( JOY_FAILED_TO_CALIBRATE );
-		Con_Printf( "Calibration failed, got samples %d < %d\n", gyrocal.samples, min_samples );
-		return;
+		if( !gyrocal.continuous )
+		{
+			Joy_SetCalibrationState( JOY_FAILED_TO_CALIBRATE );
+			Con_Printf( S_ERROR "Calibration failed, got samples %d < %d\n", gyrocal.samples, min_samples );
+			gyrocal.time = 0.0f;
+			return;
+		}
+		// Con_Reportf( S_WARN "Continuous calibration: too few samples (%d < %d), retrying\n", gyrocal.samples, min_samples );
+	}
+	else
+	{
+		VectorScale( gyrocal.data, 1.0f / gyrocal.samples, gyrocal.calibrated_values );
+		Joy_SetCalibrationState( JOY_CALIBRATED );
+		if( !gyrocal.continuous )
+			Con_Printf( "Calibration done. Result: %f %f %f at %d samples\n", gyrocal.calibrated_values[0], gyrocal.calibrated_values[1], gyrocal.calibrated_values[2], gyrocal.samples );
+		// else
+		//	Con_Reportf( "Continuous calibration done. Result: %f %f %f at %d samples\n", gyrocal.calibrated_values[0], gyrocal.calibrated_values[1], gyrocal.calibrated_values[2], gyrocal.samples );
+		gyrocal.continuous = true;
 	}
 
-	VectorScale( gyrocal.data, 1.0f / gyrocal.samples, gyrocal.calibrated_values );
-	Joy_SetCalibrationState( JOY_CALIBRATED );
-	Con_Printf( "Calibration done. Result: %f %f %f at %d samples\n", gyrocal.calibrated_values[0], gyrocal.calibrated_values[1], gyrocal.calibrated_values[2], gyrocal.samples );
+	// schedule next calibration window
+	VectorClear( gyrocal.data );
+	gyrocal.samples = 0;
+	gyrocal.time = host.realtime + CALIBRATION_TIME;
+}
+
+static void SDLash_AccumulateCalibrationData( vec3_t data )
+{
+	// for continuous background calibration only listen for noise
+	// by comparing it with calibrated values
+	//
+	// for first calibration this might be hurtful as device might
+	// output offset data
+	if( gyrocal.continuous )
+	{
+		vec3_t calibrated;
+		VectorSubtract( data, gyrocal.calibrated_values, calibrated );
+
+		if( VectorLength( calibrated ) > 0.1f )
+			return;
+	}
+
+	VectorAdd( gyrocal.data, data, gyrocal.data );
+	gyrocal.samples++;
+
+	if( !gyrocal.continuous )
+		Joy_SetCalibrationState( JOY_CALIBRATING );
 }
 
 static void SDLash_GameControllerAddMappings( const char *name )
@@ -239,17 +279,13 @@ static void SDLash_GameControllerSensorUpdate( SDL_ControllerSensorEvent sensor
 	if( gyrocal.time != 0.0f )
 	{
 		if( host.realtime > gyrocal.time )
-		{
 			SDLash_FinalizeCalibration();
-			gyrocal.time = 0.0f;
-		}
 		else
-		{
-			VectorAdd( gyrocal.data, sensor.data, gyrocal.data );
-			gyrocal.samples++;
-			Joy_SetCalibrationState( JOY_CALIBRATING );
-		}
-		return;
+			SDLash_AccumulateCalibrationData( sensor.data );
+
+		// block gyro events only during initial calibration
+		if( !gyrocal.continuous )
+			return;
 	}
 
 	VectorSubtract( sensor.data, gyrocal.calibrated_values, data );