Nightshade: Routine at 49137

49137: Update Ghost

The routine for objects of type 136 to 139, the ghosts. A ghost drifts towards the player and hurts the player if it touches. It vanishes when the player moves more than three cells away, and turns into a burst (scoring 16 hundred points) when a shot hits it.
UpdateGhost	49137	CALL PlayGhostSound	Play the ghost's sound if the ghost has been drawn in the view.
	49140	CALL SetVelocityTowardsPlayer	Make the ghost drift towards the player.
	49143	CALL SetDirectionFromVelocity	Move the ghost.
	49146	BIT 0,(IX+7)	Jump to UpdateGhost_Burst if the ghost has been hit by something.
	49150	JR NZ,UpdateGhost_Burst
	49152	CALL MoveObject	Check whether the ghost has run into the scenery.
	49155	CALL NextSpriteNumber	Animate the ghost.
	49158	LD C,3	Set the distance at which the ghost gives up to 3 cells.
	49160	CALL CheckPlayerClose	Check whether the ghost is close to the player.
	49163	JR NC,UpdateGhost_Vanish	Jump to UpdateGhost_Vanish if the player is further away than that.
	49165	CALL CheckShotHit	Check whether a shot has hit the ghost.
	49168	JR C,UpdateGhost_ShotBurst	Jump to UpdateGhost_ShotBurst if it has.
	49170	CALL CheckPlayerCollision	Check whether the ghost is touching the player.
	49173	RET NC	Return if it is not.
	49174	JP HurtPlayer	Hurt the player (see HurtPlayer).
UpdateGhost_Vanish	49177	LD (IX+0),0	Remove the ghost, because the player has got away from it.
	49181	RET	Return.
A shot has hit the ghost.
UpdateGhost_ShotBurst	49182	LD (IY+0),12	Turn the shot that hit the ghost into a burst.
UpdateGhost_Burst	49186	LD (IX+0),12	Turn the ghost into a burst.
	49190	LD BC,16	Set the points for destroying a ghost.
	49193	JP AddToScore	Jump to AddToScore to add the points to the score.