90 lines
3.1 KiB
NASM
90 lines
3.1 KiB
NASM
; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
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; VGAs. Uses slow approach that selects the plane explicitly for each
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; pixel. Fills up to but not including the column at EndX and the row
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; at EndY. No clipping is performed.
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; C near-callable as:
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;
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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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.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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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
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shr di,1 ;X/4 = offset of first rectangle pixel in scan
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; 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
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mov es,ax ;point ES:DI to the first rectangle pixel's
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; 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 cl,byte ptr [bp+StartX]
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and cl,011b ;CL = first rectangle pixel's plane
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mov al,01h
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shl al,cl ;set only the bit for the pixel's plane to 1
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mov ah,byte ptr [bp+Color] ;color with which to fill
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mov bx,[bp+EndY]
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sub bx,[bp+StartY] ;BX = height of rectangle
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jle FillDone ;skip if 0 or negative height
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mov si,[bp+EndX]
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sub si,[bp+StartX] ;CX = width of rectangle
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jle FillDone ;skip if 0 or negative width
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FillRowsLoop:
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push ax ;remember the plane mask for the left edge
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push di ;remember the start offset of the scan line
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mov cx,si ;set count of pixels in this scan line
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FillScanLineLoop:
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out dx,al ;set the plane for this pixel
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mov es:[di],ah ;draw the pixel
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shl al,1 ;adjust the plane mask for the next pixel's
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and al,01111b ; bit, modulo 4
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jnz AddressSet ;advance address if we turned over from
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inc di ; plane 3 to plane 0
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mov al,00001b ;set plane mask bit for plane 0
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AddressSet:
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loop FillScanLineLoop
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pop di ;retrieve the start offset of the scan line
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add di,SCREEN_WIDTH ;point to the start of the next scan
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; line of the rectangle
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pop ax ;retrieve the plane mask for the left edge
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dec bx ;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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