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Graphics Programming Black Book (Special Edition)
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chapter48
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l48-2.asm
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Assembly Source File
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1997-06-18
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9KB
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177 lines
; Mode X (320x240, 256 colors) rectangle 4x4 pattern fill routine.
; Upper left corner of pattern is always aligned to a multiple-of-4
; row and column. Works on all VGAs. Uses approach of copying the
; pattern to off-screen display memory, then loading the latches with
; the pattern for each scan line and filling each scan line four
; pixels at a time. Fills up to but not including the column at EndX
; and the row at EndY. No clipping is performed.
; Tested with TASM 4.0 by Jim Mischel 12/16/94.
; C near-callable as:
;
; void FillPatternX(int StartX, int StartY, int EndX, int EndY,
; unsigned int PageBase, char* Pattern);
SC_INDEX equ 03c4h ;Sequence Controller Index register port
MAP_MASK equ 02h ;index in SC of Map Mask register
GC_INDEX equ 03ceh ;Graphics Controller Index register port
BIT_MASK equ 08h ;index in GC of Bit Mask register
PATTERN_BUFFER equ 0fffch ;offset in screen memory of the buffer used
; to store each pattern during drawing
SCREEN_SEG equ 0a000h ;segment of display memory in Mode X
SCREEN_WIDTH equ 80 ;width of screen in addresses 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
Pattern dw ? ;4x4 pattern with which to fill rectangle
parms ends
NextScanOffset equ -2 ;local storage for distance from end of one
; scan line to start of next
RectAddrWidth equ -4 ;local storage for address width of rectangle
Height equ -6 ;local storage for height of rectangle
STACK_FRAME_SIZE equ 6
.model small
.data
; Plane masks for clipping left and right edges of rectangle.
LeftClipPlaneMask db 00fh,00eh,00ch,008h
RightClipPlaneMask db 00fh,001h,003h,007h
.code
public _FillPatternX
_FillPatternX 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_SEG ;point ES to display memory
mov es,ax
;copy pattern to display memory buffer
mov si,[bp+Pattern] ;point to pattern to fill with
mov di,PATTERN_BUFFER ;point ES:DI to pattern buffer
mov dx,SC_INDEX ;point Sequence Controller Index to
mov al,MAP_MASK ; Map Mask
out dx,al
inc dx ;point to SC Data register
mov cx,4 ;4 pixel quadruplets in pattern
DownloadPatternLoop:
mov al,1 ;
out dx,al ;select plane 0 for writes
movsb ;copy over next plane 0 pattern pixel
dec di ;stay at same address for next plane
mov al,2 ;
out dx,al ;select plane 1 for writes
movsb ;copy over next plane 1 pattern pixel
dec di ;stay at same address for next plane
mov al,4 ;
out dx,al ;select plane 2 for writes
movsb ;copy over next plane 2 pattern pixel
dec di ;stay at same address for next plane
mov al,8 ;
out dx,al ;select plane 3 for writes
movsb ;copy over next plane 3 pattern pixel
; and advance address
loop DownloadPatternLoop
mov dx,GC_INDEX ;set the bit mask to select all bits
mov ax,00000h+BIT_MASK ; from the latches and none from
out dx,ax ; the CPU, so that we can write the
; latch contents directly to memory
mov ax,[bp+StartY] ;top rectangle scan line
mov si,ax
and si,011b ;top rect scan line modulo 4
add si,PATTERN_BUFFER ;point to pattern scan line that
; maps to top line of rect to draw
mov dx,SCREEN_WIDTH
mul dx ;offset in page of top rectangle scan line
mov di,[bp+StartX]
mov bx,di
shr di,1 ;X/4 = offset of first rectangle pixel in scan
shr di,1 ; line
add di,ax ;offset of first rectangle pixel in page
add di,[bp+PageBase] ;offset of first rectangle pixel in
; display memory
and bx,0003h ;look up left edge plane mask
mov ah,LeftClipPlaneMask[bx] ; to clip
mov bx,[bp+EndX]
and bx,0003h ;look up right edge plane
mov al,RightClipPlaneMask[bx] ; mask to clip
mov bx,ax ;put the masks in BX
mov cx,[bp+EndX] ;calculate # of addresses across rect
mov ax,[bp+StartX]
cmp cx,ax
jle FillDone ;skip if 0 or negative width
dec cx
and ax,not 011b
sub cx,ax
shr cx,1
shr cx,1 ;# of addresses across rectangle to fill - 1
jnz MasksSet ;there's more than one pixel to draw
and bh,bl ;there's only one pixel, so combine the left
; and right edge clip masks
MasksSet:
mov ax,[bp+EndY]
sub ax,[bp+StartY] ;AX = height of rectangle
jle FillDone ;skip if 0 or negative height
mov [bp+Height],ax
mov ax,SCREEN_WIDTH
sub ax,cx ;distance from end of one scan line to start
dec ax ; of next
mov [bp+NextScanOffset],ax
mov [bp+RectAddrWidth],cx ;remember width in addresses - 1
mov dx,SC_INDEX+1 ;point to Sequence Controller Data reg
; (SC Index still points to Map Mask)
FillRowsLoop:
mov cx,[bp+RectAddrWidth] ;width across - 1
mov al,es:[si] ;read display memory to latch this scan
; line's pattern
inc si ;point to the next pattern scan line, wrapping
jnz short NoWrap ; back to the start of the pattern if
sub si,4 ; we've run off the end
NoWrap:
mov al,bh ;put left-edge clip mask in AL
out dx,al ;set the left-edge plane (clip) mask
stosb ;draw the left edge (pixels come from latches;
; value written by CPU doesn't matter)
dec cx ;count off left edge address
js FillLoopBottom ;that's the only address
jz DoRightEdge ;there are only two addresses
mov al,00fh ;middle addresses are drawn 4 pixels at a pop
out dx,al ;set the middle pixel mask to no clip
rep stosb ;draw the middle addresses four pixels apiece
; (from latches; value written doesn't matter)
DoRightEdge:
mov al,bl ;put right-edge clip mask in AL
out dx,al ;set the right-edge plane (clip) mask
stosb ;draw the right edge (from latches; value
; written doesn't matter)
FillLoopBottom:
add di,[bp+NextScanOffset] ;point to the start of the next scan
; line of the rectangle
dec word ptr [bp+Height] ;count down scan lines
jnz FillRowsLoop
FillDone:
mov dx,GC_INDEX+1 ;restore the bit mask to its default,
mov al,0ffh ; which selects all bits from the CPU
out dx,al ; and none from the latches (the GC
; Index still points to Bit Mask)
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
_FillPatternX endp
end