; video.asm
; uses interrupts to set video mode and draw a line

include 'emu8086.inc'

org 100h ; set location counter to 100h

jmp CodeStart

DataStart:
xStart dw 50 ; x coordinate of line start
yStart dw 50 ; y coordinate of line start
length dw 25 ; length of line

CodeStart:

; set the video mode 320x200, 256 colors
mov al, 13h
mov ah, 0
int 10h 

; initialize cx (x coord) to xStart + length
mov cx, xStart
add cx, length


; loop from (xStart+length) to xStart to draw a horizontal line
LoopStart: 

; draw a pixel
; set color in al, x in cx, y in dx
mov al, 50
mov dx, yStart

; set sub function value in ah to draw a pixel
; and invoke the interrupt
mov ah, 0ch
int 10h 

mov dx, yStart
add dx,length

; decrement the x coord
sub cx, 1

; test to see if x coord has reached start value
cmp cx, xStart

; continue loop if cx >= xStart
jae LoopStart

ret