Cleanup of inertial_thrust(), and some comments

git-svn-id: svn://svn.code.sf.net/p/sc2/code/trunk@2522 8092fc87-c524-0410-9efc-e669fe64eaf9

sc2/src/sc2code/ship.c

@@ -42,9 +42,13 @@ animation_preprocess (PELEMENT ElementPtr)
 	}
 }
 
+
 UWORD
 inertial_thrust (ELEMENTPTR ElementPtr)
 {
+#define MAX_ALLOWED_SPEED     WORLD_TO_VELOCITY (DISPLAY_TO_WORLD (18))
+#define MAX_ALLOWED_SPEED_SQR ((DWORD)MAX_ALLOWED_SPEED * MAX_ALLOWED_SPEED)
+
 	COUNT CurrentAngle, TravelAngle;
 	COUNT max_thrust, thrust_increment;
 	VELOCITYPTR VelocityPtr;
@@ -54,66 +58,63 @@ inertial_thrust (ELEMENTPTR ElementPtr)
 
 	GetElementStarShip (ElementPtr, &StarShipPtr);
 	CurrentAngle = FACING_TO_ANGLE (StarShipPtr->ShipFacing);
+	TravelAngle = GetVelocityTravelAngle (VelocityPtr);
 	thrust_increment = StarShipPtr->RaceDescPtr->characteristics.thrust_increment;
 	max_thrust = StarShipPtr->RaceDescPtr->characteristics.max_thrust;
 	if (thrust_increment == max_thrust)
-	{
+	{	// inertialess acceleration (Skiff)
 		SetVelocityVector (VelocityPtr,
 				max_thrust, StarShipPtr->ShipFacing);
 		return (SHIP_AT_MAX_SPEED);
 	}
-	else if ((TravelAngle =
-			GetVelocityTravelAngle (VelocityPtr)) == CurrentAngle
+	else if (TravelAngle == CurrentAngle
 			&& (StarShipPtr->cur_status_flags
 				& (SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED))
 			&& !(StarShipPtr->cur_status_flags & SHIP_IN_GRAVITY_WELL))
+	{	// already maxed-out acceleration
 		return (StarShipPtr->cur_status_flags
 				& (SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED));
+	}
 	else
 	{
 		SIZE delta_x, delta_y;
 		SIZE cur_delta_x, cur_delta_y;
 		DWORD desired_speed, max_speed;
+		DWORD current_speed;
 
 		thrust_increment = WORLD_TO_VELOCITY (thrust_increment);
 		GetCurrentVelocityComponents (VelocityPtr, &cur_delta_x, &cur_delta_y);
-		delta_x = cur_delta_x
-				+ COSINE (CurrentAngle, thrust_increment);
-		delta_y = cur_delta_y
-				+ SINE (CurrentAngle, thrust_increment);
-		desired_speed = (DWORD)((long)delta_x * delta_x)
-				+ (DWORD)((long)delta_y * delta_y);
-		max_speed = (DWORD)WORLD_TO_VELOCITY (max_thrust)
-				* WORLD_TO_VELOCITY (max_thrust);
-		if (desired_speed <= max_speed)
-			SetVelocityComponents (VelocityPtr, delta_x, delta_y);
-		else
-		{
-#define MAX_ALLOWED_SPEED WORLD_TO_VELOCITY (DISPLAY_TO_WORLD (18))
-			DWORD current_speed;
+		current_speed = VelocitySquared (cur_delta_x, cur_delta_y);
+		delta_x = cur_delta_x + COSINE (CurrentAngle, thrust_increment);
+		delta_y = cur_delta_y + SINE (CurrentAngle, thrust_increment);
+		desired_speed = VelocitySquared (delta_x, delta_y);
+		max_speed = VelocitySquared (WORLD_TO_VELOCITY (max_thrust), 0);
 		
-			if (((StarShipPtr->cur_status_flags & SHIP_IN_GRAVITY_WELL)
-					&& desired_speed <=
-					(DWORD)MAX_ALLOWED_SPEED * (DWORD)MAX_ALLOWED_SPEED)
-					|| (current_speed =
-					(DWORD)((long)cur_delta_x * (long)cur_delta_x)
-					+ (DWORD)((long)cur_delta_y * (long)cur_delta_y)) > desired_speed)
-			{
+		if (desired_speed <= max_speed)
+		{	// normal acceleration
+			SetVelocityComponents (VelocityPtr, delta_x, delta_y);
+		}
+		else if (((StarShipPtr->cur_status_flags & SHIP_IN_GRAVITY_WELL)
+				&& desired_speed <= MAX_ALLOWED_SPEED_SQR)
+				|| desired_speed < current_speed)
+		{	// acceleration in a gravity well within max allowed
+			// deceleration after gravity whip
 			SetVelocityComponents (VelocityPtr, delta_x, delta_y);
 			return (SHIP_AT_MAX_SPEED | SHIP_BEYOND_MAX_SPEED);
 		}
 		else if (TravelAngle == CurrentAngle)
-			{
+		{	// normal max acceleration, same vector
 			if (current_speed <= max_speed)
-					SetVelocityVector (VelocityPtr,
-							max_thrust, StarShipPtr->ShipFacing);
+				SetVelocityVector (VelocityPtr, max_thrust,
+						StarShipPtr->ShipFacing);
 			return (SHIP_AT_MAX_SPEED);
 		}
 		else
-			{
-				VELOCITY_DESC v;
+		{	// maxed-out acceleration at an angle to current travel vector
+			// thrusting at an angle while at max velocity only changes
+			// the travel vector, but does not really change the velocity
 
-				v = *VelocityPtr;
+			VELOCITY_DESC v = *VelocityPtr;
 
 			DeltaVelocityComponents (&v,
 					COSINE (CurrentAngle, thrust_increment >> 1)
@@ -121,8 +122,7 @@ inertial_thrust (ELEMENTPTR ElementPtr)
 					SINE (CurrentAngle, thrust_increment >> 1)
 					- SINE (TravelAngle, thrust_increment));
 			GetCurrentVelocityComponents (&v, &cur_delta_x, &cur_delta_y);
-				desired_speed = (long)cur_delta_x * (long)cur_delta_x
-						+ (long)cur_delta_y * (long)cur_delta_y;
+			desired_speed = VelocitySquared (cur_delta_x, cur_delta_y);
 			if (desired_speed > max_speed)
 			{
 				if (desired_speed < current_speed)
@@ -132,7 +132,6 @@ inertial_thrust (ELEMENTPTR ElementPtr)
 
 			*VelocityPtr = v;
 		}
-		}
 
 		return (0);
 	}

sc2/src/sc2code/velocity.h

@@ -47,6 +47,12 @@ extern void SetVelocityComponents (VELOCITYPTR velocityptr, SIZE dx, SIZE
 extern void DeltaVelocityComponents (VELOCITYPTR velocityptr, SIZE dx,
 		SIZE dy);
 
+static inline DWORD
+VelocitySquared (SIZE dx, SIZE dy)
+{
+	return (DWORD)((long)dx * dx + (long)dy * dy);
+}
+
 #define VELOCITY_SHIFT 5
 #define VELOCITY_SCALE (1<<VELOCITY_SHIFT)