Robotron: 2084: Routine at CEDF

Per-entity frame handler for an approaching narrow entity. Advances the animation phase counter, moves the entity down by six pixels per frame, and on the final frame installs Handle_Homing_Enemy as the entity's new handler. Called from Main_Game_Loop.

Per-entity frame handler for an approaching narrow entity. Advances the animation phase counter, moves the entity down by six pixels per frame, and on the final frame installs Handle_Homing_Enemy as the entity's new handler. Called from Main_Game_Loop.
Step_Narrow_Entity_Approach	CEDF	INC HL	Step past the entity type byte.
	CEE0	EX DE,HL	Copy the entity pointer to DE.
	CEE1	LD HL,($C535)	Advance the animation phase counter by 40.
	CEE4	LD BC,$0040
	CEE7	ADD HL,BC
	CEE8	LD ($C535),HL
	CEEB	EX DE,HL	Copy the entity pointer back to HL.
	CEEC	LD A,D	Jump to Step_Narrow_Entity_Approach_Wrap to wrap the approach at the screen boundary.
	CEED	CP $0F
	CEEF	JR Z,Step_Narrow_Entity_Approach_Wrap
	CEF1	JR NC,Step_Narrow_Entity_Approach_Advance_Six	Jump to Step_Narrow_Entity_Approach_Advance_Six if the entity's approach descent is complete.
	CEF3	EXX	Load the entity draw colour.
	CEF4	LD B,A
	CEF5	INC B
	CEF6	EXX
	CEF7	PUSH HL	Draw the entity sprite.
	CEF8	CALL Draw_Clipped_Wide_Sprite
	CEFB	POP HL
	CEFC	INC HL	Move the entity six pixels down the screen.
	CEFD	LD A,(HL)
	CEFE	ADD A,$06
	CF00	LD (HL),A
	CF01	DEC HL	Step back within the entity record.
	CF02	LD A,($C536)	Skip spawning if this is not the final approach frame.
	CF05	CP $01
	CF07	JR NZ,Step_Narrow_Entity_Approach_Draw
	CF09	EXX	Switch to the entity arrival colour INK: YELLOW, PAPER: BLACK (BRIGHT) .
	CF0A	LD B,$46
	CF0C	EXX
	CF0D	PUSH HL	Draw the entity's arrival frame.
	CF0E	CALL Draw_Entity_Sprite
	CF11	POP HL
	CF12	DEC HL	Install Handle_Homing_Enemy as the entity's new handler to begin homing on the player.
	CF13	DEC HL
	CF14	LD DE,$CD50
	CF17	LD (HL),D
	CF18	DEC HL
	CF19	LD (HL),E
	CF1A	LD DE,$0009	Advance nine bytes to the next entity record.
	CF1D	JR Step_Narrow_Entity_Approach_Advance	Advance nine bytes to the next entity record.
Step_Narrow_Entity_Approach_Wrap	CF1F	INC HL	Reset the descent position to wrap the approach path.
	CF20	LD A,(HL)
	CF21	SUB $54
	CF23	LD (HL),A
	CF24	DEC HL	Step back and prepare the draw colour.
	CF25	LD A,D	Step back and prepare the draw colour.
Step_Narrow_Entity_Approach_Draw	CF26	EXX	Load the draw colour.
	CF27	LD B,A
	CF28	EXX
	CF29	PUSH HL	Draw the entity sprite.
	CF2A	CALL Draw_Clipped_Wide_Sprite
	CF2D	POP HL
Step_Narrow_Entity_Approach_Advance_Six	CF2E	LD DE,$0006	Prepare to advance past this entity record.
Step_Narrow_Entity_Approach_Advance	CF31	ADD HL,DE	Advance to the next entity record and return.
	CF32	RET	Advance to the next entity record and return.