; Transforms the 1/16-pixel on-screen Y coordinate [sy] to its corresponding
; VRAM line given the current scrolling offset.

; int pascal near scroll_subpixel_y_to_vram(int sy);
public SCROLL_SUBPIXEL_Y_TO_VRAM_SEG1
scroll_subpixel_y_to_vram_seg1	proc near
@@sy	= word ptr 2

	mov	bx, sp
	mov	ax, ss:[bx+@@sy]
	sar	ax, 4
	cmp	_scroll_active, 0
	jz	short @@lt0?
	add	ax, _scroll_line

@@lt0?:
	or	ax, ax
	jge	short @@lt400?
	add	ax, RES_Y
	jmp	short @@ret

@@lt400?:
	cmp	ax, RES_Y
	jl	short @@ret
	sub	ax, RES_Y

@@ret:
	ret	2
scroll_subpixel_y_to_vram_seg1	endp