A83: Check this Pixel Routine. =)

To: assembly-83@lists.ticalc.org
Subject: A83: Check this Pixel Routine. =)
From: Jkhum98@aol.com
Date: Sat, 19 Dec 1998 19:35:51 EST
Delivered-To: assembly-83-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-83@lists.ticalc.org


I put together this Routine that plots a Pixel to the Graph Buffer.  The
purpose I had in "writing" it was to utilize the GetPix Routine that is in
ZLIB. I do not take much credit for it because Joe did the hard part in
writing GetPix, but I wanted to Organize this so that a value could be
inputted to make it either plot the pixel White, plot it Black, or XOR it...
Can somebody look over it and see it will actually work?  Also, somebody give
suggestions on a better way to do this, but keep in mind this is the path I
want to take because I like programming for SOS and wanted to make use of that
Library Routine. Thanks in advance for any responses... =)
															--Jason K.

;-------------------------------------------	;
; SOS Pixel Plotting Routine - By Jason K.	;
;-------------------------------------------	;
; Input:  D = X,  E = Y,  C = Pixel Color.	;
;			(0-Clear,  1-Plot,  2-XOR Pixel).	;
; Output: Pixel is Plotted to Graph Buffer.	;
;-------------------------------------------	;

PIXEL:
	push de			; Save the Coordinates
	ld a, c			; Load this to check which Color
	cp 0
	call z, PIXEL_WHITE
	cp 1
	call z, PIXEL_BLACK
	cp 2
	call z, PIXEL_XORIT
	pop de				; Retrieve Coords for other Routines
	ret		

PIXEL_WHITE:
	ld a, d			; 'a' now has X Coordinate
	call GETPIX		; Call the Pixel Routine from ZLIB
	AND (hl)			; 'AND' to clear pixel
	ld (hl), a			; Write the new byte to Graph Buffer
	ld a, 0			; Reload this for use with the CPs above
	ret

PIXEL_BLACK:
	ld a, d			; 'a' now has X Coordinate
	call GETPIX		; Call the Pixel Routine from ZLIB
	OR (hl)			; 'OR' to plot pixel
	ld (hl), a			; Write the new byte to Graph Buffer
	ld a, 1			; Reload this for use with the CPs above
	ret	

PIXEL_XORIT:
	ld a, d			; 'a' now has X Coordinate
	call GETPIX		; Call the Pixel Routine from ZLIB
	XOR (hl)			; 'XOR' to toggle pixel
	ld (hl), a			; Write the new byte to Graph Buffer
	ret					; No need to reload A, done with CPs.


*NOTE* here is the Information for the GetPix Routine:
	Getpix (lib C) - Get byte/bit for a pixel.
	Input:  a=x coordinate  e=y coordinate
	Output: a holds bit of pixel
			 hl->byte of pixel on the graph buffer.
	Registers destroyed: af bc de hl