Smoke - Average

gistfile1.asm

bloom:

	mov	cx, 63680		; we average every pixel except the top row
	mov	di, 320			; we start at the 2nd row
	
next_avg:
	xor	ax, ax			; clear out our accumulator
	
	mov	al, es:[di]		; get the current pixel
	
	add	al, es:[di-1] 		; add the pixel to the left
	adc	ah, 0			; adjust for overflow
	
	add	al, es:[di+1] 		; add the pixel to the right
	adc	ah, 0			; adjust for overflow
	
	add	al, es:[di-320]		; add the pixel above
	adc	ah, 0			; adjust for overflow
	
	shr	ax, 2			; divide by 4 to get the average
	
	cmp	al, 0			; can we dampen?
	jz	no_damp			; jump over if we can't
	
	dec	al			; dampen the colour by 1
	
no_damp:
	mov	es:[di-320], al		; put the averaged pixel 1 pixel above
	
	inc	di			; next pixel
	dec	cx			; keep count of how many we've got left
	jnz	next_avg
	
	ret