(svn r21106) -Change: Tuned realistic acceleration to be a bit more realistic in order to make acceleration "slower", which highlights the differences between vehicle types more.

src/ground_vehicle.cpp

@@ -30,12 +30,11 @@ void GroundVehicle<T, Type>::PowerChanged()
 	uint16 max_track_speed = v->GetDisplayMaxSpeed();
 
 	for (const T *u = v; u != NULL; u = u->Next()) {
-		uint32 current_power = u->GetPower();
+		uint32 current_power = u->GetPower() + u->GetPoweredPartPower(u);
 		total_power += current_power;
 
 		/* Only powered parts add tractive effort. */
 		if (current_power > 0) max_te += u->GetWeight() * u->GetTractiveEffort();
-		total_power += u->GetPoweredPartPower(v);
 		number_of_parts++;
 
 		/* Get minimum max speed for this track. */
@@ -43,8 +42,6 @@ void GroundVehicle<T, Type>::PowerChanged()
 		if (track_speed > 0) max_track_speed = min(max_track_speed, track_speed);
 	}
 
-	this->acc_cache.cached_axle_resistance = 60 * number_of_parts;
-
 	byte air_drag;
 	byte air_drag_value = v->GetAirDrag();
 
@@ -87,11 +84,14 @@ void GroundVehicle<T, Type>::CargoChanged()
 	for (T *u = T::From(this); u != NULL; u = u->Next()) {
 		uint32 current_weight = u->GetWeight();
 		weight += current_weight;
-		u->acc_cache.cached_slope_resistance = current_weight * u->GetSlopeSteepness();
+		/* Slope steepness is in percent, result in N. */
+		u->acc_cache.cached_slope_resistance = current_weight * u->GetSlopeSteepness() * 100;
 	}
 
 	/* Store consist weight in cache. */
 	this->acc_cache.cached_weight = max<uint32>(1, weight);
+	/* Friction in bearings and other mechanical parts is 0.1% of the weight (result in N). */
+	this->acc_cache.cached_axle_resistance = 10 * weight;
 
 	/* Now update vehicle power (tractive effort is dependent on weight). */
 	this->PowerChanged();
@@ -106,7 +106,7 @@ int GroundVehicle<T, Type>::GetAcceleration() const
 {
 	/* Templated class used for function calls for performance reasons. */
 	const T *v = T::From(this);
-	int32 speed = v->GetCurrentSpeed();
+	int32 speed = v->GetCurrentSpeed(); // [km/h-ish]
 
 	/* Weight is stored in tonnes. */
 	int32 mass = this->acc_cache.cached_weight;
@@ -120,16 +120,15 @@ int GroundVehicle<T, Type>::GetAcceleration() const
 
 	const int area = v->GetAirDragArea();
 	if (!maglev) {
-		resistance = (13 * mass) / 10;
+		/* Static resistance plus rolling friction. */
-		resistance += this->acc_cache.cached_axle_resistance;
+		resistance = this->acc_cache.cached_axle_resistance;
-		resistance += (v->GetRollingFriction() * mass * speed) / 1000;
+		resistance += mass * v->GetRollingFriction();
-		resistance += (area * this->acc_cache.cached_air_drag * speed * speed) / 10000;
-	} else {
-		resistance += (area * this->acc_cache.cached_air_drag * speed * speed) / 20000;
 	}
+	/* Air drag; the air drag coefficient is in an arbitrary NewGRF-unit,
+	 * so we need some magic conversion factor. */
+	resistance += (area * this->acc_cache.cached_air_drag * speed * speed) / 500;
 
 	resistance += this->GetSlopeResistance();
-	resistance *= 4; //[N]
 
 	/* This value allows to know if the vehicle is accelerating or braking. */
 	AccelStatus mode = v->GetAccelerationStatus();
@@ -138,9 +137,8 @@ int GroundVehicle<T, Type>::GetAcceleration() const
 	int force;
 	if (speed > 0) {
 		if (!maglev) {
-			force = power / speed; //[N]
+			/* Conversion factor from km/h to m/s is 5/18 to get [N] in the end. */
-			force *= 22;
+			force = power * 18 / (speed * 5);
-			force /= 10;
 			if (mode == AS_ACCEL && force > max_te) force = max_te;
 		} else {
 			force = power / 25;

src/ground_vehicle.hpp

@@ -30,12 +30,12 @@ struct AccelerationCache {
 	uint32 cached_weight;           ///< Total weight of the consist.
 	uint32 cached_slope_resistance; ///< Resistance caused by weight when this vehicle part is at a slope.
 	uint32 cached_max_te;           ///< Maximum tractive effort of consist.
+	uint16 cached_axle_resistance;  ///< Resistance caused by the axles of the vehicle.
 
 	/* Cached values, recalculated on load and each time a vehicle is added to/removed from the consist. */
+	uint16 cached_max_track_speed;  ///< Maximum consist speed limited by track type.
 	uint32 cached_power;            ///< Total power of the consist.
 	uint32 cached_air_drag;         ///< Air drag coefficient of the vehicle.
-	uint16 cached_axle_resistance;  ///< Resistance caused by the axles of the vehicle.
-	uint16 cached_max_track_speed;  ///< Maximum consist speed limited by track type.
 };
 
 /** Ground vehicle flags. */

src/roadveh.h

@@ -217,11 +217,11 @@ protected: // These functions should not be called outside acceleration code.
 
 	/**
 	 * Gets the area used for calculating air drag.
-	 * @return Area of the engine.
+	 * @return Area of the engine in m^2.
 	 */
 	FORCEINLINE byte GetAirDragArea() const
 	{
-		return 60;
+		return 6;
 	}
 
 	/**
@@ -244,21 +244,25 @@ protected: // These functions should not be called outside acceleration code.
 
 	/**
 	 * Calculates the current speed of this vehicle.
-	 * @return Current speed in mph.
+	 * @return Current speed in km/h-ish.
 	 */
 	FORCEINLINE uint16 GetCurrentSpeed() const
 	{
-		return this->cur_speed * 10 / 32;
+		return this->cur_speed / 2;
 	}
 
 	/**
 	 * Returns the rolling friction coefficient of this vehicle.
-	 * @return Rolling friction coefficient in [1e-3].
+	 * @return Rolling friction coefficient in [1e-4].
 	 */
 	FORCEINLINE uint32 GetRollingFriction() const
 	{
-		/* Trams have a slightly greater friction coefficient than trains. The rest of road vehicles have bigger values. */
+		/* Trams have a slightly greater friction coefficient than trains.
-		return (this->roadtype == ROADTYPE_TRAM) ? 50 : 75;
+		 * The rest of road vehicles have bigger values. */
+		uint32 coeff = (this->roadtype == ROADTYPE_TRAM) ? 40 : 75;
+		/* The friction coefficient increases with speed in a way that
+		 * it doubles at 128 km/h, triples at 256 km/h and so on. */
+		return coeff * (128 + this->GetCurrentSpeed()) / 128;
 	}
 
 	/**
@@ -276,7 +280,7 @@ protected: // These functions should not be called outside acceleration code.
 	 */
 	FORCEINLINE uint32 GetSlopeSteepness() const
 	{
-		return 20 * _settings_game.vehicle.roadveh_slope_steepness; // 1% slope * slope steepness
+		return _settings_game.vehicle.roadveh_slope_steepness;
 	}
 
 	/**

src/train.h

@@ -438,11 +438,12 @@ protected: // These functions should not be called outside acceleration code.
 
 	/**
 	 * Gets the area used for calculating air drag.
-	 * @return Area of the engine.
+	 * @return Area of the engine in m^2.
 	 */
 	FORCEINLINE byte GetAirDragArea() const
 	{
-		return 120;
+		/* Air drag is higher in tunnels due to the limited cross-section. */
+		return (this->track == TRACK_BIT_WORMHOLE && this->vehstatus & VS_HIDDEN) ? 28 : 14;
 	}
 
 	/**
@@ -465,20 +466,24 @@ protected: // These functions should not be called outside acceleration code.
 
 	/**
 	 * Calculates the current speed of this vehicle.
-	 * @return Current speed in mph.
+	 * @return Current speed in km/h-ish.
 	 */
 	FORCEINLINE uint16 GetCurrentSpeed() const
 	{
-		return this->cur_speed * 10 / 16;
+		return this->cur_speed;
 	}
 
 	/**
 	 * Returns the rolling friction coefficient of this vehicle.
-	 * @return Rolling friction coefficient in [1e-3].
+	 * @return Rolling friction coefficient in [1e-4].
 	 */
 	FORCEINLINE uint32 GetRollingFriction() const
 	{
-		return 35;
+		/* Rolling friction for steel on steel is between 0.1% and 0.2%,
+		 * but we use a higher value here to get better game-play results.
+		 * The friction coefficient increases with speed in a way that
+		 * it doubles at 512 km/h, triples at 1024 km/h and so on. */
+		return 30 * (512 + this->GetCurrentSpeed()) / 512;
 	}
 
 	/**
@@ -496,7 +501,7 @@ protected: // These functions should not be called outside acceleration code.
 	 */
 	FORCEINLINE uint32 GetSlopeSteepness() const
 	{
-		return 20 * _settings_game.vehicle.train_slope_steepness; // 1% slope * slope steepness
+		return _settings_game.vehicle.train_slope_steepness;
 	}
 
 	/**