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