(svn r20299) -Add: Make trains and road vehicles use a different area value to calculate air drag.

src/ground_vehicle.cpp

@@ -107,7 +107,7 @@ int GroundVehicle<T, Type>::GetAcceleration() const
 
 	bool maglev = v->GetAccelerationType() == 2;
 
-	const int area = 120;
+	const int area = v->GetAirDragArea();
 	if (!maglev) {
 		resistance = (13 * mass) / 10;
 		resistance += this->acc_cache.cached_axle_resistance;

src/ground_vehicle.hpp

@@ -54,6 +54,7 @@ enum GroundVehicleFlags {
  * virtual uint16      GetPoweredPartPower(const T *head) const = 0;
  * virtual uint16      GetWeight() const = 0;
  * virtual byte        GetTractiveEffort() const = 0;
+ * virtual byte        GetAirDragArea() const = 0;
  * virtual AccelStatus GetAccelerationStatus() const = 0;
  * virtual uint16      GetCurrentSpeed() const = 0;
  * virtual uint32      GetRollingFriction() const = 0;

src/roadveh.h

@@ -210,6 +210,15 @@ protected: // These functions should not be called outside acceleration code.
 		return RoadVehInfo(this->engine_type)->tractive_effort;
 	}
 
+ 	/**
+	 * Gets the area used for calculating air drag.
+	 * @return Area of the engine.
+	 */
+	FORCEINLINE byte GetAirDragArea() const
+	{
+		return 60;
+	}
+
 	/**
 	 * Checks the current acceleration status of this vehicle.
 	 * @return Acceleration status.

src/train.h

@@ -432,6 +432,15 @@ protected: // These functions should not be called outside acceleration code.
 		return GetVehicleProperty(this, PROP_TRAIN_TRACTIVE_EFFORT, RailVehInfo(this->engine_type)->tractive_effort);
 	}
 
+	/**
+	 * Gets the area used for calculating air drag.
+	 * @return Area of the engine.
+	 */
+	FORCEINLINE byte GetAirDragArea() const
+	{
+		return 120;
+	}
+
 	/**
 	 * Checks the current acceleration status of this vehicle.
 	 * @return Acceleration status.