113 lines
3.9 KiB
NASM
113 lines
3.9 KiB
NASM
; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
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; VGAs. Uses fast approach that fans data out to up to four planes at
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; once to draw up to four pixels at once. Fills up to but not
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; including the column at EndX and the row at EndY. No clipping is
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; performed.
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; C near-callable as:
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; void FillRectangleX(int StartX, int StartY, int EndX, int EndY,
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; unsigned int PageBase, int Color);
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SC_INDEX equ 03c4h ;Sequence Controller Index
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MAP_MASK equ 02h ;index in SC of Map Mask register
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SCREEN_SEG equ 0a000h ;segment of display memory in mode X
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SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
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; to the next
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parms struc
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dw 2 dup (?) ;pushed BP and return address
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StartX dw ? ;X coordinate of upper left corner of rect
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StartY dw ? ;Y coordinate of upper left corner of rect
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EndX dw ? ;X coordinate of lower right corner of rect
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; (the row at EndX is not filled)
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EndY dw ? ;Y coordinate of lower right corner of rect
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; (the column at EndY is not filled)
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PageBase dw ? ;base offset in display memory of page in
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; which to fill rectangle
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Color dw ? ;color in which to draw pixel
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parms ends
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.model small
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.data
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; Plane masks for clipping left and right edges of rectangle.
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LeftClipPlaneMask db 00fh,00eh,00ch,008h
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RightClipPlaneMask db 00fh,001h,003h,007h
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.code
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public _FillRectangleX
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_FillRectangleX proc near
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push bp ;preserve caller's stack frame
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mov bp,sp ;point to local stack frame
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push si ;preserve caller's register variables
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push di
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cld
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mov ax,SCREEN_WIDTH
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mul [bp+StartY] ;offset in page of top rectangle scan line
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mov di,[bp+StartX]
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shr di,1 ;X/4 = offset of first rectangle pixel in scan
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shr di,1 ; line
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add di,ax ;offset of first rectangle pixel in page
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add di,[bp+PageBase] ;offset of first rectangle pixel in
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; display memory
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mov ax,SCREEN_SEG ;point ES:DI to the first rectangle
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mov es,ax ; pixel's address
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mov dx,SC_INDEX ;set the Sequence Controller Index to
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mov al,MAP_MASK ; point to the Map Mask register
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out dx,al
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inc dx ;point DX to the SC Data register
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mov si,[bp+StartX]
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and si,0003h ;look up left edge plane mask
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mov bh,LeftClipPlaneMask[si] ; to clip & put in BH
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mov si,[bp+EndX]
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and si,0003h ;look up right edge plane
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mov bl,RightClipPlaneMask[si] ; mask to clip & put in BL
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mov cx,[bp+EndX] ;calculate # of addresses across rect
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mov si,[bp+StartX]
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cmp cx,si
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jle FillDone ;skip if 0 or negative width
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dec cx
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and si,not 011b
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sub cx,si
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shr cx,1
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shr cx,1 ;# of addresses across rectangle to fill - 1
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jnz MasksSet ;there's more than one byte to draw
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and bh,bl ;there's only one byte, so combine the left
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; and right edge clip masks
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MasksSet:
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mov si,[bp+EndY]
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sub si,[bp+StartY] ;BX = height of rectangle
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jle FillDone ;skip if 0 or negative height
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mov ah,byte ptr [bp+Color] ;color with which to fill
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mov bp,SCREEN_WIDTH ;stack frame isn't needed any more
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sub bp,cx ;distance from end of one scan line to start
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dec bp ; of next
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FillRowsLoop:
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push cx ;remember width in addresses - 1
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mov al,bh ;put left-edge clip mask in AL
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out dx,al ;set the left-edge plane (clip) mask
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mov al,ah ;put color in AL
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stosb ;draw the left edge
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dec cx ;count off left edge byte
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js FillLoopBottom ;that's the only byte
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jz DoRightEdge ;there are only two bytes
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mov al,00fh ;middle addresses are drawn 4 pixels at a pop
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out dx,al ;set the middle pixel mask to no clip
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mov al,ah ;put color in AL
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rep stosb ;draw the middle addresses four pixels apiece
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DoRightEdge:
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mov al,bl ;put right-edge clip mask in AL
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out dx,al ;set the right-edge plane (clip) mask
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mov al,ah ;put color in AL
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stosb ;draw the right edge
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FillLoopBottom:
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add di,bp ;point to the start of the next scan line of
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; the rectangle
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pop cx ;retrieve width in addresses - 1
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dec si ;count down scan lines
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jnz FillRowsLoop
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FillDone:
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pop di ;restore caller's register variables
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pop si
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pop bp ;restore caller's stack frame
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ret
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_FillRectangleX endp
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end
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