#.md

Final(?) magnet implementation for GB Robbo

C using 0xCyyx  8072	11	412/  1204/ 733.8
C using map[]	5772	11	300/  944/  524.7
ASM		5060	11	276/  872/  460.0

magnet.asm

	.title  "magnets_s"
	.module magnets_s

	.area _CODE
	newRobboY			=	15
	newRobboX			=	14
	robboMagnetDrag		=	13
	DIR_RIGHT			=	0x0
	DIR_LEFT			=	0x2
	DIR_NONE			=	0x8
	TILE_MAGNET_RIGHT	=	0x0c
	TILE_MAGNET_LEFT	=	0x1c
	
	.globl _playSound
	.globl _currentState
	
_checkMagnet::
	ld		a,		(#(_currentState + newRobboY))
;================		b => currentState.newRobboY .... temporally
	ld		b,	a

	swap	a
	and		a,	#0x0f
	or		a,	#0xc0
;================		h => hiAddress = 0xc0 | (currentState.newRobboY >> 4)  hiAddress will not change
	ld		h,	a

	ld		a,	b
	swap	a
	and		a,	#0xf0
;================		d => lowY = currentState.newRobboY << 4
	ld		d,	a

	ld		a,	(#(_currentState + newRobboX))
;================		b => currentState.newRobboX			loop counter
	ld		b,	a
;================		e => currentState.newRobboX			for left loop counter		ld a,(a16) is costly
	ld		e,	a

	or		a,	d	
	inc		a
;================		l => currentState.newRobboX | lowY + 1
	ld		l,	a

loopStartRight$:
;================		while ++b != 16		x is [0..15]
	inc		b
	ld		a,	b
	sub		a,	#0x10
	jr		Z,	checkLeft$

;================		we already have tile address in hl so we load and increment hl
	ld		a,	(hl+)

;================		is tile a magnet?
	cp		a,	#TILE_MAGNET_LEFT
	jr		NZ,	checkIfRightTileNotEmpty$

;================		yes? robbo slowly dying ... set dragging state to drag to right
	ld		hl,		#(_currentState + robboMagnetDrag)
	ld		(hl),	#DIR_RIGHT

;================		play magnet sound
	ld		de,	#_magnetSound
	push	de
	call	_playSound
	pop		hl
	ret

checkIfRightTileNotEmpty$:
;===============		any non empty(0) tile blocks magnet
	or		a,	a
	jr		Z,	loopStartRight$

checkLeft$:

	ld		a,	e
	or		a,	d
	dec		a
;================		l => currentState.newRobboX | lowY - 1
	ld		l,	a

loopStartLeft$:
;================		while --e != 255
	dec		e
	ld		a, e
	sub		a, #0xff
	jr		Z,	magnetNotFound$

;================		we already have tile address in hl so we load and decrement hl
	ld		a,	(hl-)

;================		is tile a magnet? 
	cp		a,	#TILE_MAGNET_RIGHT
	jr		NZ,	checkIfLeftTileNotEmpty$

;================		yes? roboo is slowly dying ... set dragging state to drag to left
	ld		hl,		#(_currentState + robboMagnetDrag)
	ld		(hl),	#DIR_LEFT

;================		play magnet sound
	ld		de,	#_magnetSound
	push	de
	call	_playSound
	pop		hl
	ret

checkIfLeftTileNotEmpty$:
;===============		any non empty(0) tile blocks magnet
	or		a,	a
	jr		Z,	loopStartLeft$

magnetNotFound$:
;================		no magnets found set dragging state to drag to none ... robbo is safe
	ld		hl,	#(_currentState + robboMagnetDrag)
	ld		(hl),#DIR_NONE
	ret

magnet_cyyx.c

#define MAKE_ADDRESS(hiAddress, loAddress) ((uint8_t*)(((hiAddress) << 8) | (loAddress)))

void checkMagneta()
{
	uint8_t hiAddress = 0xc0 | (currentState.newRobboY >> 4);
	uint8_t lowY = currentState.newRobboY << 4;
	uint8_t nextX = currentState.newRobboX;
	while (++nextX != 16)
	{
		uint8_t tile = *(MAKE_ADDRESS(hiAddress, nextX | lowY));
		if (tile == TILE_MAGNET_LEFT)
		{
			currentState.robboMagnetDrag = DIR_RIGHT;
			playSound(magnetSound);
			return;
		}
		else if (tile != TILE_EMPTY)
			break;
	};
	uint8_t prevX = currentState.newRobboX;
	while (--prevX != 255)
	{
		uint8_t tile1 = *(MAKE_ADDRESS(hiAddress, prevX | lowY));
		if (tile1 == TILE_MAGNET_RIGHT)
		{
			currentState.robboMagnetDrag = DIR_LEFT;
			playSound(magnetSound);
			return;
		}
		else if (tile1 != TILE_EMPTY)
			break;
	};
	currentState.robboMagnetDrag = DIR_NONE;
}

magnet_map.c

void checkMagnetb()
{
	uint8_t* mapY = currentLevel.map + 16 * currentState.newRobboY;
	uint8_t nextX = currentState.newRobboX;
	while (++nextX != 16)
	{
		uint8_t tile = *(mapY + nextX);
		if (tile == TILE_MAGNET_LEFT)
		{
			currentState.robboMagnetDrag = DIR_RIGHT;
			playSound(magnetSound);
			return;
		}
		else if (tile != TILE_EMPTY)
			break;
	};
	uint8_t prevX = currentState.newRobboX;
	while (--prevX != 255)
	{
		uint8_t tile1 = *(mapY + prevX);
		if (tile1 == TILE_MAGNET_RIGHT)
		{
			currentState.robboMagnetDrag = DIR_LEFT;
			playSound(magnetSound);
			return;
		}
		else if (tile1 != TILE_EMPTY)
			break;
	};
	currentState.robboMagnetDrag = DIR_NONE;
}