Knight Lore: Routine at B5FF

The ball_bounce block (ball_bounce). Falls under gravity, and every time it lands it jumps again and picks a new heading: two units a frame along X or along Y, chosen at random, pointing towards the player if the player is Sabrewulf and away if he is Sabreman. It keeps that heading all the way through the air, however often a wall stops it. The frame flips between the two types every frame, and it kills on contact.

Which way "towards" means is decided by patching two JR instructions rather than by testing: see bounce_ball_set_sense.

The ball_bounce block (ball_bounce). Falls under gravity, and every time it lands it jumps again and picks a new heading: two units a frame along X or along Y, chosen at random, pointing towards the player if the player is Sabrewulf and away if he is Sabreman. It keeps that heading all the way through the air, however often a wall stops it. The frame flips between the two types every frame, and it kills on contact. Which way "towards" means is decided by patching two JR instructions rather than by testing: see bounce_ball_set_sense.
upd_182_183	B5FF	CALL upd_12_to_15	pixel offsets for the ball sprite
	B602	LD L,(IX+$09)	keep dX and dY
	B605	LD H,(IX+$0A)
	B608	PUSH HL
	B609	LD A,(IX+$0B)	remember dZ from before the move, for the bounce sound
	B60C	LD ($5BC2),A
	B60F	CALL dec_dZ_and_update_XYZ	gravity, then move, clipped against the room and other objects
	B612	POP HL	put dX and dY back: the clipping may have cut them, but the ball keeps its heading until it bounces
	B613	LD (IX+$09),L
	B616	LD (IX+$0A),H
	B619	LD A,($5C08)	object 0's type is the player's legs: 16 to 29 for Sabreman gives $38 (JR C), anything else $30 (JR NC)
	B61C	SUB $10
	B61E	CP $20
	B620	LD A,$30
	B622	JR NC,bounce_ball_set_sense
	B624	ADD A,$08