Framerate-independent idPlayer::Move() and idAI::AdjustFlyingAngles()

thanks to Github user tyuah8:
dhewm#584 (comment)

neo/d3xp/Player.cpp

@@ -7117,8 +7117,12 @@ void idPlayer::Move( void ) {
 		if ( spectating ) {
 			SetEyeHeight( newEyeOffset );
 		} else {
+			// DG: make this framerate-independent, code suggested by tyuah8 on Github
+			// https://en.wikipedia.org/wiki/Exponential_smoothing#Time_constant
+			const float tau = -16.0f / idMath::Log( pm_crouchrate.GetFloat() );
+			const float a = 1.0f - idMath::Exp( -gameLocal.gameMsec / tau );
 			// smooth out duck height changes
-			SetEyeHeight( EyeHeight() * pm_crouchrate.GetFloat() + newEyeOffset * ( 1.0f - pm_crouchrate.GetFloat() ) );
+			SetEyeHeight( EyeHeight() * (1.0f - a) + newEyeOffset * a );
 		}
 	}
 

neo/d3xp/ai/AI.cpp

@@ -2984,8 +2984,15 @@ void idAI::AdjustFlyingAngles( void ) {
 		}
 	}
 
-	fly_roll = fly_roll * 0.95f + roll * 0.05f;
-	fly_pitch = fly_pitch * 0.95f + pitch * 0.05f;
+	// DG: make this framerate-independent, code suggested by tyuah8 on Github
+	// https://en.wikipedia.org/wiki/Exponential_smoothing#Time_constant
+	static const float tau = -16.0f / idMath::Log( 0.95f );
+	// TODO: use gameLocal.gameMsec instead, so it's not affected by slow motion?
+	//       enemies turning slower in slowmo seems logical, but the original code
+	//       just increased every tic and thus was independent of slowmo
+	const float a = 1.0f - idMath::Exp( -gameLocal.msec / tau );
+	fly_roll  = fly_roll  * (1.0f - a) + roll  * a;
+	fly_pitch = fly_pitch * (1.0f - a) + pitch * a;
 
 	if ( flyTiltJoint != INVALID_JOINT ) {
 		animator.SetJointAxis( flyTiltJoint, JOINTMOD_WORLD, idAngles( fly_pitch, 0.0f, fly_roll ).ToMat3() );

neo/game/Player.cpp

@@ -6014,8 +6014,12 @@ void idPlayer::Move( void ) {
 		if ( spectating ) {
 			SetEyeHeight( newEyeOffset );
 		} else {
+			// DG: make this framerate-independent, code suggested by tyuah8 on Github
+			// https://en.wikipedia.org/wiki/Exponential_smoothing#Time_constant
+			const float tau = -16.0f / idMath::Log( pm_crouchrate.GetFloat() );
+			const float a = 1.0f - idMath::Exp( -gameLocal.gameMsec / tau );
 			// smooth out duck height changes
-			SetEyeHeight( EyeHeight() * pm_crouchrate.GetFloat() + newEyeOffset * ( 1.0f - pm_crouchrate.GetFloat() ) );
+			SetEyeHeight( EyeHeight() * (1.0f - a) + newEyeOffset * a );
 		}
 	}
 

neo/game/ai/AI.cpp

@@ -2896,8 +2896,12 @@ void idAI::AdjustFlyingAngles( void ) {
 		}
 	}
 
-	fly_roll = fly_roll * 0.95f + roll * 0.05f;
-	fly_pitch = fly_pitch * 0.95f + pitch * 0.05f;
+	// DG: make this framerate-independent, code suggested by tyuah8 on Github
+	// https://en.wikipedia.org/wiki/Exponential_smoothing#Time_constant
+	static const float tau = -16.0f / idMath::Log( 0.95f );
+	const float a = 1.0f - idMath::Exp( -gameLocal.msec / tau );
+	fly_roll  = fly_roll  * (1.0f - a) + roll  * a;
+	fly_pitch = fly_pitch * (1.0f - a) + pitch * a;
 
 	if ( flyTiltJoint != INVALID_JOINT ) {
 		animator.SetJointAxis( flyTiltJoint, JOINTMOD_WORLD, idAngles( fly_pitch, 0.0f, fly_roll ).ToMat3() );