Deathchase: Routine at 5E00

5E00: Move the trees

Used by the routines at 65B3, 663D, 69E3 and 6AC2.
5E00	LD A,($5DE8)	Is the bike moving?
5E03	DEC A	Invert flag
5E04	RET NZ	Return if the bike isn't moving
5E05	LD A,($64F3)	Get the next bit pattern
5E08	AND A
5E09	RRCA	Shift from "all odds" <-> "all evens"
5E0A	LD ($64F3),A
5E0D	JR NC,$5E21	If "evens" -> "odds", don't generate trees
5E0F	CALL $6491	Generate a random number, return the next item in A
5E12	LD H,$5B	Get the portion of trees to copy
5E14	AND $7F	Position back to the start of the line
5E16	ADD A,$20
5E18	LD L,A
5E19	LD DE,$7CBE	Put the new line of trees on the back row
5E1C	LD BC,$001E
5E1F	LDDR
5E21	LD HL,$7F7F	Shift the other lines up one so they appear closer
5E24	LD DE,$7F9F
5E27	LD BC,$02E0
5E2A	LDDR
As trees get closer to the player, shunt the left out to the side, to emulate the correct perspective view
5E2C	XOR A
5E2D	LD B,$0D	13 rows
5E2F	LD HL,$7F62	Point to next row
5E32	LD DE,$7F61
5E35	LD A,$0E	14 columns
5E37	PUSH BC
5E38	PUSH DE
5E39	LD B,$00
5E3B	LD C,A
5E3C	LDIR
5E3E	DEC L
5E3F	LD (HL),$00
5E41	POP HL
5E42	LD DE,$FFE0
5E45	ADD HL,DE
5E46	PUSH HL
5E47	INC HL
5E48	POP DE
5E49	POP BC
5E4A	BIT 1,B
5E4C	JR Z,$5E51
5E4E	DEC A
5E4F	JR Z,$5E53
5E51	DJNZ $5E37
5E53	LD B,$0D
5E55	LD HL,$7F7D
5E58	LD DE,$7F7E
5E5B	LD A,$0D
5E5D	PUSH BC
5E5E	PUSH DE
5E5F	LD B,$00
5E61	LD C,A
5E62	LDDR
5E64	INC L
5E65	LD (HL),$00
5E67	POP HL
5E68	LD DE,$FFE0
5E6B	ADD HL,DE
5E6C	PUSH HL
5E6D	DEC HL
5E6E	POP DE
5E6F	POP BC
5E70	BIT 1,B
5E72	JR Z,$5E77
5E74	DEC A
5E75	JR Z,$5E79
5E77	DJNZ $5E5D
As trees get closer to the player, shunt the right out to the side, to emulate the correct perspective view
5E79	XOR A
5E7A	LD B,$06
5E7C	LD HL,$7CA0
5E7F	LD DE,$7CA1
5E82	LD (HL),A
5E83	LD BC,$001F
5E86	LDIR
5E88	LD HL,$7F42
5E8B	LD DE,$7F41
5E8E	LD BC,$000E
5E91	LDIR
5E93	LD (DE),A
5E94	LD DE,$7F61
5E97	LD HL,$7F62
5E9A	LD BC,$000E
5E9D	LDIR
5E9F	LD (DE),A
5EA0	LD HL,$7F7D
5EA3	LD DE,$7F7E
5EA6	LD BC,$000D
5EA9	LDDR
5EAB	LD (DE),A	Don't put two trees next to each other
5EAC	LD HL,$7F40
5EAF	LD BC,$0040
5EB2	LD A,$40
5EB4	CPIR
5EB6	DEC HL
5EB7	LD (HL),$00
5EB9	INC HL
5EBA	LD A,B
5EBB	OR C
5EBC	JR NZ,$5EB2
5EBE	LD HL,$7F40
5EC1	LD BC,$0040
5EC4	LD A,$20
5EC6	CPIR
5EC8	LD (HL),$40
5ECA	LD A,B
5ECB	OR C
5ECC	JR NZ,$5EC4
5ECE	XOR A
5ECF	LD B,$04
5ED1	PUSH BC
5ED2	LD HL,$7F81
5ED5	LD DE,$7F80
5ED8	LD BC,$000F
5EDB	LDIR
5EDD	LD (DE),A
5EDE	POP BC
5EDF	DJNZ $5ED1
Expand out the closest trees to take up more area, as perspective view would anticipate
5EE1	LD BC,$0020
5EE4	LD A,$20
5EE6	LD HL,$7F80
5EE9	CPIR
5EEB	LD (HL),$20
5EED	INC HL
5EEE	LD (HL),$40
5EF0	INC HL
5EF1	LD (HL),$40
5EF3	LD DE,$7F9E
5EF6	EX DE,HL
5EF7	AND A
5EF8	SBC HL,DE
5EFA	EX DE,HL
5EFB	JR NC,$5EE9
5EFD	RET