Fix all(?) vehicle handling problems at high FPS. Refactor FIX_BUGS i…

…n ProcessWheel() to be much simpler.

src/entities/Physical.cpp

@@ -590,7 +590,12 @@ CPhysical::ApplyAirResistance(void)
 	}else if(GetStatus() != STATUS_GHOST){ 
 		float f = Pow(1.0f/Abs(1.0f + m_fAirResistance*0.5f*m_vecMoveSpeed.MagnitudeSqr()), CTimer::GetTimeStep());
 		m_vecMoveSpeed *= f;
+#ifdef FIX_BUGS
+		// Fix too much friction at high FPS (evil cause of bad vehicle handling, rear tires unable to lose traction, etc!)
+		m_vecTurnSpeed *= Pow(0.99f, CTimer::GetTimeStepFix());
+#else
 		m_vecTurnSpeed *= 0.99f;
+#endif
 	}
 }
 
@@ -1071,6 +1076,10 @@ CPhysical::ApplyFriction(CPhysical *B, float adhesiveLimit, CColPoint &colpoint)
 		if(fOtherSpeedA > speedSum){
 			impulseA = (speedSum - fOtherSpeedA) * A->m_fMass;
 			impulseB = (speedSum - fOtherSpeedB) * B->m_fMass;
+#ifdef FIX_BUGS
+			impulseA *= CTimer::GetTimeStepFix();
+			impulseB *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep();
 			if(impulseA < -impulseLimit) impulseA = -impulseLimit;
 #ifdef FIX_BUGS
@@ -1107,6 +1116,10 @@ CPhysical::ApplyFriction(CPhysical *B, float adhesiveLimit, CColPoint &colpoint)
 		if(fOtherSpeedA > speedSum){
 			impulseA = (speedSum - fOtherSpeedA) * A->m_fMass;
 			impulseB = (speedSum - fOtherSpeedB) * massB;
+#ifdef FIX_BUGS
+			impulseA *= CTimer::GetTimeStepFix();
+			impulseB *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep();
 			if(impulseA < -impulseLimit) impulseA = -impulseLimit;
 			if(impulseB > impulseLimit) impulseB = impulseLimit;
@@ -1140,6 +1153,10 @@ CPhysical::ApplyFriction(CPhysical *B, float adhesiveLimit, CColPoint &colpoint)
 		if(fOtherSpeedA > speedSum){
 			impulseA = (speedSum - fOtherSpeedA) * massA;
 			impulseB = (speedSum - fOtherSpeedB) * B->m_fMass;
+#ifdef FIX_BUGS
+			impulseA *= CTimer::GetTimeStepFix();
+			impulseB *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep();
 			if(impulseA < -impulseLimit) impulseA = -impulseLimit;
 			if(impulseB > impulseLimit) impulseB = impulseLimit;
@@ -1174,6 +1191,10 @@ CPhysical::ApplyFriction(CPhysical *B, float adhesiveLimit, CColPoint &colpoint)
 		if(fOtherSpeedA > speedSum){
 			impulseA = (speedSum - fOtherSpeedA) * massA;
 			impulseB = (speedSum - fOtherSpeedB) * massB;
+#ifdef FIX_BUGS
+			impulseA *= CTimer::GetTimeStepFix();
+			impulseB *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep();
 			if(impulseA < -impulseLimit) impulseA = -impulseLimit;
 			if(impulseB > impulseLimit) impulseB = impulseLimit;
@@ -1214,6 +1235,9 @@ CPhysical::ApplyFriction(float adhesiveLimit, CColPoint &colpoint)
 			// not really impulse but speed
 			// maybe use ApplyFrictionMoveForce instead?
 			fImpulse = -fOtherSpeed;
+#ifdef FIX_BUGS
+			fImpulse *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep() / m_fMass;
 			if(fImpulse < -impulseLimit) fImpulse = -impulseLimit;
 			CVector vImpulse = frictionDir*fImpulse;
@@ -1235,6 +1259,9 @@ CPhysical::ApplyFriction(float adhesiveLimit, CColPoint &colpoint)
 			frictionDir = vOtherSpeed * (1.0f/fOtherSpeed);
 #endif
 			fImpulse = -fOtherSpeed * m_fMass;
+#ifdef FIX_BUGS
+			fImpulse *= CTimer::GetTimeStepFix();
+#endif
 			impulseLimit = adhesiveLimit*CTimer::GetTimeStep() * 1.5;
 			if(fImpulse < -impulseLimit) fImpulse = -impulseLimit;
 			ApplyFrictionMoveForce(frictionDir*fImpulse);

src/vehicles/Automobile.cpp

@@ -857,8 +857,12 @@ CAutomobile::ProcessControl(void)
 			   (m_aSuspensionSpringRatio[1] < 1.0f || m_aSuspensionSpringRatio[3] < 1.0f))
 				ApplyTurnForce(-GRAVITY*Min(m_fTurnMass, 2500.0f)*GetUp(), -1.0f*GetForward());
 		}
-
+#ifdef FIX_BUGS
+		// Keep brake non-timestepped (so the later ProcessWheel() takes only non-timestepped inputs)
+		brake = m_fBrakePedal * pHandling->fBrakeDeceleration * CTimer::GetDefaultTimeStep();
+#else
 		brake = m_fBrakePedal * pHandling->fBrakeDeceleration * CTimer::GetTimeStep();
+#endif
 		bool neutralHandling = GetStatus() != STATUS_PLAYER && GetStatus() != STATUS_PLAYER_REMOTE && (pHandling->Flags & HANDLING_NEUTRALHANDLING);
 		float brakeBiasFront = neutralHandling ? 1.0f : 2.0f*pHandling->fBrakeBias;
 		float brakeBiasRear  = neutralHandling ? 1.0f : 2.0f-pHandling->fBrakeBias;	// looks like a bug, but it was correct in III...
@@ -1058,12 +1062,7 @@ CAutomobile::ProcessControl(void)
 			float rearBrake = brake;
 			float rearTraction = traction;
 			if(bIsHandbrakeOn){
-#ifdef FIX_BUGS
-				// Not sure if this is needed, but brake usually has timestep as a factor
-				rearBrake = 20000.0f * CTimer::GetTimeStepFix();
-#else
 				rearBrake = 20000.0f;
-#endif
 				if(fwdSpeed > 0.1f && pHandling->Flags & HANDLING_HANDBRAKE_TYRE){
 					m_fTireTemperature += 0.005*CTimer::GetTimeStep();
 					if(m_fTireTemperature > 2.0f)
@@ -1072,8 +1071,11 @@ CAutomobile::ProcessControl(void)
 			}else if(m_doingBurnout && mod_HandlingManager.HasRearWheelDrive(pHandling->nIdentifier)){
 				rearBrake = 0.0f;
 				rearTraction = 0.0f;
-				// BUG: missing timestep
+#ifdef FIX_BUGS
+				ApplyTurnForce(contactPoints[CARWHEEL_REAR_LEFT], -0.001f*m_fTurnMass*m_fSteerAngle*GetRight()*CTimer::GetTimeStepFix());
+#else
 				ApplyTurnForce(contactPoints[CARWHEEL_REAR_LEFT], -0.001f*m_fTurnMass*m_fSteerAngle*GetRight());
+#endif
 			}else if(m_fTireTemperature > 1.0f){
 				rearTraction *= m_fTireTemperature;
 			}

src/vehicles/Transmission.cpp

@@ -125,7 +125,12 @@ cTransmission::CalculateDriveAcceleration(const float &gasPedal, uint8 &gear, fl
 	float targetVelocity = Gears[gear].fMaxVelocity*speedMul*fCheat;
 	float accel = (targetVelocity - fVelocity) * (fEngineAcceleration*accelMul) / Abs(targetVelocity);
 	if(Abs(fVelocity) < Abs(Gears[gear].fMaxVelocity*fCheat))
+#ifdef FIX_BUGS
+		// The acceleration provided by a transmission+engine should not depend on framelength.
+		fAcceleration = gasPedal * accel;
+#else
 		fAcceleration = gasPedal * accel * CTimer::GetTimeStep();
+#endif
 	else
 		fAcceleration = 0.0f;
 	return fAcceleration;

src/vehicles/Vehicle.cpp

@@ -788,7 +788,14 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 	bAlreadySkidding = false;
 #endif
 
-	// how much force we want to apply in these axes
+	// Velocity impulses fwd and right.  Units are like meters per second.
+	// This function was written assuming a fixed FPS, so a correction is made
+	// right at the end before actually applying these impulses.
+	//
+	// Note that many functions in this engine deal with "force impulses" rather
+	// than "velocity impulses".  They are directly related: F=ma.  It is
+	// possible that the original devs actually used force impulses here but
+	// an optimising compiler re-arranged their maths.
 	float fwd = 0.0f;
 	float right = 0.0f;
 
@@ -804,36 +811,30 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 		bAlreadySkidding = true;
 	*wheelState = WHEEL_STATE_NORMAL;
 
+#ifdef FIX_BUGS
+	// Everything else here is timestep independent, let's stay with this theme to keep the rest of the FPS bugfixes simpler.
+	adhesion *= CTimer::GetDefaultTimeStep();
+#else
 	adhesion *= CTimer::GetTimeStep();
+#endif
 	if(bAlreadySkidding)
 		adhesion *= pHandling->fTractionLoss;
 
 	// moving sideways
 	if(contactSpeedRight != 0.0f){
 		// exert opposing force
 		right = -contactSpeedRight/wheelsOnGround;
-		// BUG?
-		// contactSpeedRight is independent of framerate but right has timestep as a factor
-		// so we probably have to fix this
-		// fixing this causes jittery cars at 15fps, and causes the car to move backwards slowly at 18fps
-		// at 19fps, the effects are gone ...
-		//right *= CTimer::GetTimeStepFix();
 
 		if(wheelStatus == WHEEL_STATUS_BURST){
 			float fwdspeed = Min(contactSpeedFwd, fBurstSpeedMax);
-#ifdef FIX_BUGS
-			// Keep the effect running at the same frequency even when the game is at high FPS
-			right += fwdspeed * CGeneral::GetRandomNumberInRange(-fBurstTyreMod, fBurstTyreMod) * CTimer::GetLogicalFramesPassed();
-#else
 			right += fwdspeed * CGeneral::GetRandomNumberInRange(-fBurstTyreMod, fBurstTyreMod);
-#endif
 		}
 	}
 
 	if(bDriving){
 		fwd = thrust;
 
-		// limit sideways force (why?)
+		// Limit sideways forces applied by the tires to the max the tires can possibly do.
 		if(right > 0.0f){
 			if(right > adhesion)
 				right = adhesion;
@@ -843,11 +844,6 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 		}
 	}else if(contactSpeedFwd != 0.0f){
 		fwd = -contactSpeedFwd/wheelsOnGround;
-#ifdef FIX_BUGS
-		// contactSpeedFwd is independent of framerate but fwd has timestep as a factor
-		// so we probably have to fix this
-		fwd *= CTimer::GetTimeStepFix();
-#endif
 
 		if(!bBraking){
 			if(m_fGasPedal < 0.01f){
@@ -859,9 +855,6 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 					brake = 0.2f * mod_HandlingManager.fWheelFriction / pHandling->fMass;
 				else
 					brake = mod_HandlingManager.fWheelFriction / pHandling->fMass;
-#ifdef FIX_BUGS
-				brake *= CTimer::GetTimeStepFix();
-#endif
 			}
 		}
 
@@ -888,10 +881,10 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 				*wheelState = WHEEL_STATE_SKIDDING;
 		}
 
-		float l = Sqrt(speedSq);
+		float speed = Sqrt(speedSq);
 		float tractionLoss = bAlreadySkidding ? 1.0f : pHandling->fTractionLoss;
-		right *= adhesion * tractionLoss / l;
-		fwd *= adhesion * tractionLoss / l;
+		right *= adhesion * tractionLoss / speed;
+		fwd   *= adhesion * tractionLoss / speed;
 	}
 
 	if(fwd != 0.0f || right != 0.0f){
@@ -923,9 +916,19 @@ CVehicle::ProcessWheel(CVector &wheelFwd, CVector &wheelRight, CVector &wheelCon
 		else
 			turnDirection = direction;
 
+
+		// Curious: there is a perfectly good ApplyMoveSpeed() function that 
+		// takes "velocity impulses", but instead we use the ApplyMoveForce() 
+		// function which takes a "force impulse" instead and then fix up the
+		// difference by multiplying in the vehicle mass (F=ma).  Possibly 
+		// evidence that an optimising compiler re-arranged the arithmetic?
 		float impulse = speed*m_fMass;
 		float turnImpulse = turnSpeed*GetMass(wheelContactPoint, turnDirection);
 
+#ifdef FIX_BUGS
+		impulse     = impulse     * CTimer::GetTimeStepFix();
+		turnImpulse = turnImpulse * CTimer::GetTimeStepFix();
+#endif
 		ApplyMoveForce(impulse * direction);
 		ApplyTurnForce(turnImpulse * turnDirection, wheelContactPoint);
 	}
@@ -949,7 +952,14 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 	bAlreadySkidding = false;
 #endif
 
-	// how much force we want to apply in these axes
+	// Velocity impulses fwd and right.  Units are like meters per second.
+	// This function was written assuming a fixed FPS, so a correction is made
+	// right at the end before actually applying these impulses.
+	//
+	// Note that many functions in this engine deal with "force impulses" rather
+	// than "velocity impulses".  They are directly related: F=ma.  It is
+	// possible that the original devs actually used force impulses here but
+	// an optimising compiler re-arranged their maths.
 	float fwd = 0.0f;
 	float right = 0.0f;
 
@@ -966,7 +976,12 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 		bAlreadySkidding = true;
 	*wheelState = WHEEL_STATE_NORMAL;
 
+#ifdef FIX_BUGS
+	// Everything else here is timestep independent, let's stay with this theme to keep the rest of the FPS bugfixes simpler.
+	adhesion *= CTimer::GetDefaultTimeStep();
+#else
 	adhesion *= CTimer::GetTimeStep();
+#endif
 	if(bAlreadySkidding)
 		adhesion *= pHandling->fTractionLoss;
 
@@ -979,20 +994,10 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 	if(contactSpeedRight != 0.0f){
 		// exert opposing force
 		right = -contactSpeedRight/wheelsOnGround;
-#ifdef FIX_BUGS
-		// contactSpeedRight is independent of framerate but right has timestep as a factor
-		// so we probably have to fix this
-		right *= CTimer::GetTimeStepFix();
-#endif
 
 		if(wheelStatus == WHEEL_STATUS_BURST){
 			float fwdspeed = Min(contactSpeedFwd, fBurstBikeSpeedMax);		
-#ifdef FIX_BUGS
-			// Keep the effect running at the same frequency even when the game is at high FPS
-			right += fwdspeed * CGeneral::GetRandomNumberInRange(-fBurstBikeTyreMod, fBurstBikeTyreMod) * CTimer::GetLogicalFramesPassed();
-#else
 			right += fwdspeed * CGeneral::GetRandomNumberInRange(-fBurstBikeTyreMod, fBurstBikeTyreMod);
-#endif
 		}
 	}
 
@@ -1009,12 +1014,6 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 		}
 	}else if(contactSpeedFwd != 0.0f){
 		fwd = -contactSpeedFwd/wheelsOnGround;
-#ifdef FIX_BUGS
-		// contactSpeedFwd is independent of framerate but fwd has timestep as a factor
-		// so we probably have to fix this
-		fwd *= CTimer::GetTimeStepFix();
-#endif
-
 		if(!bBraking){
 			if(m_fGasPedal < 0.01f){
 				if(IsBike())
@@ -1025,9 +1024,6 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 					brake = 0.2f * mod_HandlingManager.fWheelFriction / m_fMass;
 				else
 					brake = mod_HandlingManager.fWheelFriction / m_fMass;
-#ifdef FIX_BUGS
-				brake *= CTimer::GetTimeStepFix();
-#endif
 			}
 		}
 
@@ -1078,6 +1074,10 @@ CVehicle::ProcessBikeWheel(CVector &wheelFwd, CVector &wheelRight, CVector &whee
 
 		float impulse = speed*m_fMass;
 		float turnImpulse = speed*GetMass(wheelContactPoint, direction);
+#ifdef FIX_BUGS
+		impulse     = impulse     * CTimer::GetTimeStepFix();
+		turnImpulse = turnImpulse * CTimer::GetTimeStepFix();
+#endif
 		CVector vTurnImpulse = turnImpulse * direction;
 		ApplyMoveForce(impulse * direction);