; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
; VGAs. Uses medium-speed approach that selects each plane only once
; per rectangle; this results in a fade-in effect for large
; rectangles. Fills up to but not including the column at EndX and the
; row at EndY. No clipping is performed.
; C near-callable as:
;
;    void FillRectangleX(int StartX, int StartY, int EndX, int EndY,
;	unsigned int PageBase, int Color);

SC_INDEX	equ	03c4h	;Sequence Controller Index
MAP_MASK	equ	02h	;index in SC of Map Mask register
SCREEN_SEG	equ	0a000h	;segment of display memory in mode X
SCREEN_WIDTH	equ	80	;width of screen in bytes from one scan line
				; to the next
parms struc
	dw	2 dup (?)	;pushed BP and return address
StartX	dw	?		;X coordinate of upper left corner of rect
StartY	dw	?		;Y coordinate of upper left corner of rect
EndX	dw	?		;X coordinate of lower right corner of rect
				; (the row at EndX is not filled)
EndY	dw	?		;Y coordinate of lower right corner of rect
				; (the column at EndY is not filled)
PageBase dw	?		;base offset in display memory of page in
				; which to fill rectangle
Color	dw	?		;color in which to draw pixel
parms ends

_StartOffset equ -2		;local storage for start offset of rectangle
_Width	 equ	 -4		;local storage for address width of rectangle
_Height	 equ	 -6		;local storage for height of rectangle
_PlaneInfo equ	 -8		;local storage for plane # and plane mask
STACK_FRAME_SIZE equ 8

	.model	small
	.code
	public	_FillRectangleX
_FillRectangleX proc	near
	push	bp		;preserve caller's stack frame
	mov	bp,sp		;point to local stack frame
	sub	sp,STACK_FRAME_SIZE ;allocate space for local vars
	push	si		;preserve caller's register variables
	push	di

	cld
	mov	ax,SCREEN_WIDTH
	mul	[bp+StartY]	;offset in page of top rectangle scan line
	mov	di,[bp+StartX]
	shr	di,1
	shr	di,1		;X/4 = offset of first rectangle pixel in scan
				; line
	add	di,ax		;offset of first rectangle pixel in page
	add	di,[bp+PageBase] ;offset of first rectangle pixel in
				; display memory
	mov	ax,SCREEN_SEG
	mov	es,ax		;point ES:DI to the first rectangle pixel's
	mov	[bp+_StartOffset],di ; address
	mov	dx,SC_INDEX	;set the Sequence Controller Index to
	mov	al,MAP_MASK	; point to the Map Mask register
	out	dx,al
	mov	bx,[bp+EndY]
	sub	bx,[bp+StartY]	;BX = height of rectangle
	jle	FillDone	;skip if 0 or negative height
	mov	[bp+_Height],bx
	mov	dx,[bp+EndX]
	mov	cx,[bp+StartX]
	cmp	dx,cx
	jle	FillDone	;skip if 0 or negative width
	dec	dx
	and	cx,not 011b
	sub	dx,cx
	shr	dx,1
	shr	dx,1
	inc	dx		;# of addresses across rectangle to fill
	mov	[bp+_Width],dx
	mov	word ptr [bp+_PlaneInfo],0001h
				;lower byte = plane mask for plane 0,
				; upper byte = plane # for plane 0
FillPlanesLoop:
	mov	ax,word ptr [bp+_PlaneInfo]
	mov	dx,SC_INDEX+1	;point DX to the SC Data register
	out	dx,al		;set the plane for this pixel
	mov	di,[bp+_StartOffset] ;point ES:DI to rectangle start
	mov	dx,[bp+_Width]
	mov	cl,byte ptr [bp+StartX]
	and	cl,011b		;plane # of first pixel in initial byte
	cmp	ah,cl		;do we draw this plane in the initial byte?
	jae	InitAddrSet ;yes
	dec	dx		;no, so skip the initial byte
	jz	FillLoopBottom ;skip this plane if no pixels in it
	inc	di
InitAddrSet:
	mov	cl,byte ptr [bp+EndX]
	dec	cl
	and	cl,011b		;plane # of last pixel in final byte
	cmp	ah,cl		;do we draw this plane in the final byte?
	jbe	WidthSet	;yes
	dec	dx		;no, so skip the final byte
	jz	FillLoopBottom	;skip this planes if no pixels in it
WidthSet:
	mov	si,SCREEN_WIDTH
	sub	si,dx		;distance from end of one scan line to start
				; of next
	mov	bx,[bp+_Height]	;# of lines to fill
	mov	al,byte ptr [bp+Color] ;color with which to fill
FillRowsLoop:
	mov	cx,dx		;# of bytes across scan line
	rep	stosb		;fill the scan line in this plane
	add	di,si		;point to the start of the next scan
				; line of the rectangle
	dec	bx		;count down scan lines
	jnz	FillRowsLoop
FillLoopBottom:
	mov	ax,word ptr [bp+_PlaneInfo]
	shl	al,1		;set the plane bit to the next plane
	inc	ah		;increment the plane #
	mov	word ptr [bp+_PlaneInfo],ax
	cmp	ah,4		;have we done all planes?
	jnz	FillPlanesLoop	;continue if any more planes
FillDone:
	pop	di		;restore caller's register variables
	pop	si
	mov	sp,bp		;discard storage for local variables
	pop	bp		;restore caller's stack frame
	ret
_FillRectangleX endp
	end