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Graphics Programming Black Book (Special Edition)
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disk1
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source
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chapter48
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l48-4.asm
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Assembly Source File
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1997-06-18
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6KB
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122 lines
; Mode X (320x240, 256 colors) system memory to display memory copy
; routine. Uses approach of changing the plane for each pixel copied;
; this is slower than copying all pixels in one plane, then all pixels
; in the next plane, and so on, but it is simpler; besides, images for
; which performance is critical should be stored in off-screen memory
; and copied to the screen via the latches. Copies up to but not
; including the column at SourceEndX and the row at SourceEndY. No
; clipping is performed.
; Tested with TASM 4.0 by Jim Mischel 12/16/94.
; C near-callable as:
;
; void CopySystemToScreenX(int SourceStartX, int SourceStartY,
; int SourceEndX, int SourceEndY, int DestStartX,
; int DestStartY, char* SourcePtr, unsigned int DestPageBase,
; int SourceBitmapWidth, int DestBitmapWidth);
SC_INDEX equ 03c4h ;Sequence Controller Index register port
MAP_MASK equ 02h ;index in SC of Map Mask register
SCREEN_SEG equ 0a000h ;segment of display memory in Mode X
parms struc
dw 2 dup (?) ;pushed BP and return address
SourceStartX dw ? ;X coordinate of upper left corner of source
SourceStartY dw ? ;Y coordinate of upper left corner of source
SourceEndX dw ? ;X coordinate of lower right corner of source
; (the row at EndX is not copied)
SourceEndY dw ? ;Y coordinate of lower right corner of source
; (the column at EndY is not copied)
DestStartX dw ? ;X coordinate of upper left corner of dest
DestStartY dw ? ;Y coordinate of upper left corner of dest
SourcePtr dw ? ;pointer in DS to start of bitmap in which
; source resides
DestPageBase dw ? ;base offset in display memory of page in
; which dest resides
SourceBitmapWidth dw ? ;# of pixels across source bitmap
DestBitmapWidth dw ? ;# of pixels across dest bitmap
; (must be a multiple of 4)
parms ends
RectWidth equ -2 ;local storage for width of rectangle
LeftMask equ -4 ;local storage for left rect edge plane mask
STACK_FRAME_SIZE equ 4
.model small
.code
public _CopySystemToScreenX
_CopySystemToScreenX 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
mov ax,[bp+SourceBitmapWidth]
mul [bp+SourceStartY] ;top source rect scan line
add ax,[bp+SourceStartX]
add ax,[bp+SourcePtr] ;offset of first source rect pixel
mov si,ax ; in DS
mov ax,[bp+DestBitmapWidth]
shr ax,1 ;convert to width in addresses
shr ax,1
mov [bp+DestBitmapWidth],ax ;remember address width
mul [bp+DestStartY] ;top dest rect scan line
mov di,[bp+DestStartX]
mov cx,di
shr di,1 ;X/4 = offset of first dest rect pixel in
shr di,1 ; scan line
add di,ax ;offset of first dest rect pixel in page
add di,[bp+DestPageBase] ;offset of first dest rect pixel
; in display memory
and cl,011b ;CL = first dest pixel's plane
mov al,11h ;upper nibble comes into play when plane wraps
; from 3 back to 0
shl al,cl ;set the bit for the first dest pixel's plane
mov [bp+LeftMask],al ; in each nibble to 1
mov cx,[bp+SourceEndX] ;calculate # of pixels across
sub cx,[bp+SourceStartX] ; rect
jle CopyDone ;skip if 0 or negative width
mov [bp+RectWidth],cx
mov bx,[bp+SourceEndY]
sub bx,[bp+SourceStartY] ;BX = height of rectangle
jle CopyDone ;skip if 0 or negative height
mov dx,SC_INDEX ;point to SC Index register
mov al,MAP_MASK
out dx,al ;point SC Index reg to the Map Mask
inc dx ;point DX to SC Data reg
CopyRowsLoop:
mov ax,[bp+LeftMask]
mov cx,[bp+RectWidth]
push si ;remember the start offset in the source
push di ;remember the start offset in the dest
CopyScanLineLoop:
out dx,al ;set the plane for this pixel
movsb ;copy the pixel to the screen
rol al,1 ;set mask for next pixel's plane
cmc ;advance destination address only when
sbb di,0 ; wrapping from plane 3 to plane 0
; (else undo INC DI done by MOVSB)
loop CopyScanLineLoop
pop di ;retrieve the dest start offset
add di,[bp+DestBitmapWidth] ;point to the start of the
; next scan line of the dest
pop si ;retrieve the source start offset
add si,[bp+SourceBitmapWidth] ;point to the start of the
; next scan line of the source
dec bx ;count down scan lines
jnz CopyRowsLoop
CopyDone:
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
_CopySystemToScreenX endp
end