A86: help with game

To: assembly-86@lists.ticalc.org
Subject: A86: help with game
From: BrncAvFan2@aol.com
Date: Mon, 17 Aug 1998 19:39:29 EDT
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org

I am having trouble with this program.  I know that it may seem very large to
look at but I think that it may be easier to find the problem if you copy and
paste it and use it with your emulator.  That way you have an idea of where it
messes up.  It is a program that has a little man go left or right on the
screen.  It just draws lines but it will do something when you push either
right or left.  The escape button works so don't worry about it crashing your
calc (if you chose to do it that way).

#include "ti86asm.inc"
#include "asm86.h"
#include "Ram86.inc"
#include "ti86abs.inc"


.org _asm_exec_ram

	call _clrScrn
	call _runindicoff
	ld b,25
	ld c,25
	ld de,PIC
	call PutSprite
	
Main_Prog:
	call GET_KEY
	cp K_EXIT
	ret z
	cp K_LEFT
	jp z,LEFT
	cp K_RIGHT
	jp z,RIGHT
	jp Main_Prog

LEFT:
	inc b
	call PutSprite
	jp Main_Prog

RIGHT:
	dec b
	call PutSprite
	jp Main_Prog

PIC:
	.db %00111100
	.db %01000010
	.db %00111100
	.db %00011000
	.db %01111110
	.db %00011000
	.db %00100100
	.db %01000010
	
PutSprite:

	push bc				;Save BC (X,Y)
	push de				;Save DE
	push hl				;Save HL (Start of Sprite Data)
	push hl

	push bc
	ld d,c
	ld e,b
	call FindPixel		;Finds pixel at E,D
	pop bc
						;PutSprite needs pixel at B,C
		
						;A = Bitmask with one bit set; this will be the bit (pixel) "counter"

	ex de,hl			;DE = Address in Display of Sprite
	pop hl				;HL = Start of Sprite Data
	ld b,(hl)			;B = X width of Sprite
	inc hl				;Next byte
	ld c,(hl)			;C = Y width of Sprite
	inc hl				;Next byte (now pointing at actual sprite data)
	push hl				;Save the twice incremented HL into stack
	pop ix				;IX = The recently twice incremented HL

	ex de,hl			;HL = Address in Display of Sprite

PS_NewRow:
	push bc				;Save X width of Sprite and Y width of Sprite
	ld d,(ix)			;D = (IX), so D = First byte from Sprite
	inc ix				;IX points to next row
	push af				;Save Bitmask
	push hl				;Save HL, Address in Display of Sprite

PS_NewCol:				;Now the fun begins, remember a is the bitmask, D = the Left
Column Byte from Sprite
	rl d				;Rotate D left through carry, Leftmost pixel of Sprite is carry
	ld e,a				;E = bitmask
	jr nc,PS_NoPixel	;Check pixel from sprite to see if it is set
	or (hl)				;Sets Pixel at the "current bit" (Bitmask is the "bit counter")
	ld (hl),a			;(HL) = A, Save changes to
	jr PS_NextPixel		

PS_NoPixel:
	cpl					;Invert Bitmask
	and (hl)			;Clears pixel at the "current bit" (Bitmask is the "bit counter")
	ld (hl),a			;(HL) = A Save changes

PS_NextPixel:
	ld a,e				;A = Bitmask
	rrca				;A is rotated right *through* carry
	jr nc,PS_SameByte	;If the carry was set, that means that one bit set in A
(bit counter)
						; rotated all the way to the end right into carry and recycles back into
Bit 7
						; so it can be used for the next byte

	inc hl				;Go to the next byte in the display

PS_SameByte:
	djnz PS_NewCol		;B = X (width of sprite), so it loops to PS_NewCol X times.
This means that is X = 6,
						; it will Shift Right the bitmask (move the bit counter to the right) 6
times, comparing
						; each bit of the bitmask and the sprite and setting or clearing the
pixel in that
						; particular bit.  It then moves on to the next pixel.

	pop hl				;Recover HL, the Address in Display of the Sprite
	pop af				;Recover AF, A = Bitmask
	ld de,16			;DE = 16
	add hl,de			;HL = HL + 16, this moves down ONE row in the Display Area (128
width / (8 bit/pixel) = 16 bytes)
	pop bc				;Recover X_width and Y_height of Sprite
	dec c				;C = Y_height of Sprite, subtract one, which means on row of the
Sprite has been drawn

	jr nz,PS_NewRow		;If there are more rows to be drawn, go back to PS_NewRow

; No more rows.  Since there were "effectively" 3 pushes before PS_NewRow,
there must be three pops that way the
; ret statement will retrieve the correct address when it returns to the
calling program.

	pop hl
	pop de
	pop bc
	ret

; ========================================================
; Dan Eble & James Yopp FindPixel routine
; Input: D = y, E = x
; Output: HL = addr in vid mem, A = bitmask, C is modified
; ========================================================
FindPixel:
	ld hl,FP_Bits
	ld a,e
	and $07			;a = bit offset
	add a,l
	ld l,a
	adc a,h
	sub l
	ld h,a
	ld c,(hl)		;c = bitmask for (hl)
;48 t-states up to this point
	ld hl,FP_RLD
	ld (hl),d
	ld a,e			;a = x/8 (byte offset within row)
	rrca
	rrca
	rrca
	rld
	or $FC
	ld l,(hl)		;hl -> byte in vid mem
	ld h,a
	ld a,c			;now a = bitmask for (hl)
;121 t-states up to this point
	ret
FP_RLD:
	.db $00
FP_Bits:
	.db $80,$40,$20,$10,$08,$04,$02,$01

.end


THANX
Dan


P.S.-If you answer this now, I will probably not have another question for a
long time.

THANX
Follow-Ups:
Re: A86: help with game
From: Tercero <tercero@busprod.com>