Deathchase: Routine at 637C

637C: Move the plane across screen

Used by the routine at 633A.
637C	LD A,($5DCA)	Get the enemy offset
637F	LD HL,$7CB0
6382	LD (HL),$00
6384	INC L
6385	LD (HL),$00
6387	CP $08	Is it above 8?
6389	JR C,$63CD	Jump if so
638B	CP $14	Is it below 14?
638D	LD IX,($5DCD)	Get the current screen offset
6391	JR NC,$63B2	Jump if below 14
6393	INC IX	Move down a line
6395	INC IX
6397	INC IX
6399	LD H,(IX+$01)	Get the offset to draw at
639C	LD L,(IX+$00)
639F	EX DE,HL
63A0	LD HL,$4860	Make the offset the distance up from the horizon
63A3	AND A
63A4	SBC HL,DE
63A6	JR NC,$63AC
63A8	LD IX,$650F
63AC	LD ($5DCD),IX	Set the new position
63B0	JR $63CD
63B2	DEC IX	Move up a line
63B4	DEC IX
63B6	DEC IX
63B8	LD L,(IX+$00)	Get the offset to draw at
63BB	LD H,(IX+$01)
63BE	EX DE,HL
63BF	LD HL,$40C0	Make the offset the distance from the horizon
63C2	AND A
63C3	SBC HL,DE
63C5	JR C,$63AC
63C7	LD IX,$6500
63CB	JR $63AC	Jump back to set new position, then continue
63CD	LD A,($5DCA)	Get enemy offset
63D0	LD HL,$5DE8	Is the bike moving?
63D3	BIT 0,(HL)
63D5	JR Z,$63DB
63D7	LD HL,$5DDF	Adjust enemy position to new bike position if we are turning
63DA	SUB (HL)
63DB	INC A
63DC	CP $00
63DE	JR Z,$63E4
63E0	CP $1E
63E2	JR C,$63E8
63E4	XOR A
63E5	LD ($5DCB),A	Set no bonus enemy on screen
63E8	LD ($5DCA),A	Set no bonus enemy on screen
Rotate the helecopter blades
63EB	LD A,($631B)	Graphic for left blade
63EE	XOR $2A	Invert bits 1,3 and 5
63F0	LD ($631B),A	Store it
63F3	LD A,($6323)	Graphic for right blade
63F6	XOR $2A	Invert bits 1,3 and 5
63F8	LD ($6323),A	Store it
63FB	RET