; mcgatest.asm:
;   Some buggy code...
;   It's supposed to be like an Etch-a-Sketch.
;   Can't handle boundaries in a sensible manner, though.
;   Just learning int 10h and playing around...
; assemble using:
; nasm mcgatest.asm -fbin -o mcgatest.com

	org 100h
section .text
start:
; Enter MCGA mode
	mov ax, 13h
	int 10h
; Draw pixel at (x, y)
	mov ax, 0a000h
	mov es, ax
	mov cx, 0	; y value
	mov dx, 0	; x value
repaint:
	call putpixel
; Wait for key press
	mov ah, 0h
	int 16h
; if up key:
	cmp ah, 48h
	jne notup
	dec cx
	jmp repaint
notup:
; if left key:
	cmp ah, 4bh
	jne notleft
	dec dx
	jmp repaint
notleft:
; if right key:
	cmp ah, 4dh
	jne notright
	inc dx
	jmp repaint
notright:
; if down key:
	cmp ah, 50h
	jne notdown
	inc cx
	jmp repaint
notdown:
; else return to text mode
	mov ax, 3
	int 10h
; Exit to DOS
	mov ah, 4ch
	int 21h

putpixel:
	mov bx, cx
	mov di, bx
	xchg bh, bl
	shl di, 6
	add di, bx
	mov ax, dx
	add di, ax
	mov [es:di], byte 3
	ret
	
section .data
x:	dw 1
y:	dw 1
c:	db 1
section .bss