snow - generate

gistfile1.asm

no_kbhit:

        ; put a new snowflake at the top 
        ; of the screen
	call	get_random
	mov	di, ax
	mov	byte ptr es:[di], 15

decend:

        ; we can't move snowflakes any further
        ; than the bottom of the screen so we
        ; process all other lines
	mov	di, 63680
	mov	cx, 63680
	
next_pixel:

        ; test if there is a snowflake at the 
        ; current location
	mov	al, es:[di]
	cmp	al, 0
	je	no_flake
	
        ; test if there is a snowflake beneath
        ; us at the moment
	mov	al, es:[di+320]
	cmp	al, 0
	jne	no_flake
	
        ; move the snowflake from where we are 
        ; at the moment to one line below us
	xor	al, al
	mov	byte ptr es:[di], al
	mov	al, 15
	mov	byte ptr es:[di+320], 15
	
no_flake:

        ; move our way through video memory
	dec	di
	dec	cx
	jnz	next_pixel

        ; check for a keypress
	mov	ah, 01h
	int	16h
	jz	no_kbhit