Ant Attack: Routine at 8600

Used by the routine at DRAW_VIEW.

For each object, last to first, its position relative to VIEW_ORIGIN is turned for the view and projected: the half-row is v - u - 2h and the column (u + v) / 2, where u and v are the turned coordinates and h the height. The place is height x 512 + half-row x 16 + column -- the height counting a whole pass of DRAW_SCENE -- and it goes into SPRITE_LIST with the sprite frame: the object's first frame, plus four times its animation frame, plus its facing relative to the view.

Used by the routine at DRAW_VIEW. For each object, last to first, its position relative to VIEW_ORIGIN is turned for the view and projected: the half-row is v - u - 2h and the column (u + v) / 2, where u and v are the turned coordinates and h the height. The place is height x 512 + half-row x 16 + column -- the height counting a whole pass of DRAW_SCENE -- and it goes into SPRITE_LIST with the sprite frame: the object's first frame, plus four times its animation frame, plus its facing relative to the view.
PROJECT_SPRITES	8600	LD IX,ANT5	From the fifth ant back to the player; eight objects.
	8604	LD DE,(VIEW_ORIGIN)
	8608	LD A,$08
	860A	LD HL,SPRITE_LIST
PROJECT_SPRITES_0	860D	EX AF,AF'
	860E	PUSH HL
	860F	LD B,(IX+$02)	Its height.
	8612	LD A,(IX+$00)	Its position relative to the view's origin.
	8615	SUB E
	8616	LD L,A
	8617	LD A,(IX+$01)
	861A	SUB D
	861B	LD H,A
	861C	LD A,(VIEW)	Turn it for the view: swap x and y for views 1 and 3, and negate as the view needs.
	861F	RRA
	8620	JR NC,PROJECT_SPRITES_1
	8622	LD C,H
	8623	LD H,L
	8624	LD L,C
	8625	RRA
	8626	JR NC,PROJECT_SPRITES_2
	8628	XOR A
	8629	SUB L
	862A	LD L,A
	862B	JR PROJECT_SPRITES_4
PROJECT_SPRITES_1	862D	RRA
	862E	JR NC,PROJECT_SPRITES_3
	8630	XOR A
	8631	SUB L
	8632	LD L,A
PROJECT_SPRITES_2	8633	XOR A
	8634	SUB H
	8635	LD H,A
PROJECT_SPRITES_3	8636	LD A,L	Raise it by its height.
PROJECT_SPRITES_4	8637	ADD A,B
	8638	LD L,A
	8639	LD A,H
	863A	SUB B
	863B	LD H,A
	863C	SUB L	The half-row, 0-31, or out of view.
	863D	JP PE,OFF_VIEW
	8640	CP $20
	8642	JR NC,OFF_VIEW
	8644	RLCA	Times 16, with the height above it.
	8645	RLCA
	8646	RLCA
	8647	SLA A
	8649	RL B
	864B	LD C,A
	864C	LD A,L	The column, 0-31 before halving, or out of view.
	864D	ADD A,H
	864E	JP PE,OFF_VIEW
	8651	CP $20
	8653	JR NC,OFF_VIEW
	8655	AND A	Into the place, plus one.
	8656	RRA
	8657	OR C
	8658	LD C,A
	8659	INC BC
This entry point is used by the routine at OFF_VIEW.
PROJECT_SPRITES_5	865A	POP HL	Store the place.
	865B	LD (HL),C
	865C	INC HL
	865D	LD (HL),B
	865E	INC HL
	865F	LD A,(VIEW)	The facing relative to the view.
	8662	ADD A,(IX+$04)
	8665	AND $03
	8667	LD C,A
	8668	LD A,(IX+$08)	Bit 7 set: the frame outright...
	866B	AND A
	866C	JP M,PROJECT_SPRITES_6
	866F	RLCA	...otherwise the first frame, plus four times the animation frame, plus the facing.
	8670	RLCA
	8671	ADD A,(IX+$03)
	8674	ADD A,C
PROJECT_SPRITES_6	8675	LD (HL),A
	8676	INC HL
	8677	LD BC,$FFF0	The object before: BC is -16, not an address.
	867A	ADD IX,BC	The object before: BC is -16, not an address.
	867C	EX AF,AF'
	867D	DEC A
	867E	JR NZ,PROJECT_SPRITES_0
	8680	RET