org 256

;--- B

	mov ah,0fh
	int 10h
	xor ah,ah
	push ax
	mov al,13h
	int 10h

	mov ax,0a000h
	mov es,ax

	mov cx,4
	mov dx,03c8h
	mov si,dif
	out dx,al
	inc dx	

pal	lodsb
	mov ah,al
	lodsb
	mov bh,al
	lodsb
	mov bl,al
	push cx
	mov cl,64
nxt	push si
	lodsb
	add al,ah
	xchg al,ah
	out dx,al
	lodsb
	add al,bh
	xchg al,bh
	out dx,al
	lodsb
	add al,bl
	xchg al,bl
	out dx,al
	pop si
	loop nxt
	add si,byte 3
	pop cx
	loop pal

;--- C	

	mov ch,1
	mov dx,320-256
drw	dec cx
	xor bx,bx
	mov di,320*199
	push cx
	call bcl
	inc byte [col]
	inc dx
	mov bx,199
	mov cx,dx
	mov di,256
	call bcl
	pop cx
	inc byte [col]
	inc dx
	loop drw

	mov ah,8
	int 21h
	pop ax
	int 10h
	ret

;--- A

bcl	push dx

brs	mov ax,di
	xor dx,dx
	mov bp,320
	div bp
	sub bx,ax
	jnc yup
	neg bx
	neg bp
yup	mov si,1
	sub cx,dx
	jnc xup
	neg cx
	dec si
	dec si
xup	cmp cx,bx
	jnc nsw
	xchg bx,cx
	xchg si,bp
nsw	mov dx,cx
	inc cx
	mov ax,dx
	neg ax
	sar ax,1
pix	push ax
	mov al,[col]
	stosb
	pop ax
	add ax,bx
	jnc nst
	sub ax,dx
	add di,bp
nst	add di,si
	dec di
	loop pix

	pop dx
	ret

dif	db 0,	0,	0,	0,	0,	1
	db 0,	0,	63,	1,	0,	255
	db 63,	0,	0,	255,	1,	1
	db 0,	63,	63,	1,	0,	0

col	db 0