A86: Messed Loop

To: assembly-86@lists.ticalc.org
Subject: A86: Messed Loop
From: Dave VanEe <dvanee@dowco.com>
Date: Thu, 22 Oct 1998 21:05:31 -0700
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-86@lists.ticalc.org


I'm using a Findpixel by CLEM to try to do some parabolic motion, but I
can't even get it to draw a line (diagonal Top_Left -> Bottom_Right). Why
doesn't this draw a line like that? (It draw's 2 pixels, one at 0,0 and one
around 64,32)

Vy	= $8000
Vx	= $8001
x_pos	= $8002
y_pos 	= $8003

.org _asm_exec_ram

 call _clrLCD
 ld a,0
 ld (y_pos),a
 ld (x_pos),a
 ld a,1
 ld (Vy),a
 ld (Vx),a
loop:
 ld a,(y_pos)			;load x,y of pixel
 ld c,a
 ld a,(x_pos)
 ld b,a

 call FindPixel             ;get video memory offset w/ bitmask 
 or (hl)                        ;OR bitmask with (HL) 
 ld (hl),a                     ;put result to video memory 

 ld a,(Vy)			;change x,y using Vx,Vy (velocity)
 add a,c
 ld (y_pos),a
 ld a,(Vx)
 add a,b
 ld (x_pos),a
 jr loop

(Findpixel header:)
;Input: b,c = x,y coordinates; 0-127,0-63; 0,0 = top left 
;Output: (HL) = byte in video memory, A = bitmask (ie, the precise bit in
(HL))

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