Use backtick code blocks for syntax highlighting
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James Gregory
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47-03.md
180
47-03.md
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@ -60,107 +60,111 @@ are fills, copies, and bitblts, and it's there that Mode X shines.
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**LISTING 47.2 L47-2.ASM**
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; Mode X (320x240, 256 colors) write pixel routine. Works on all VGAs.
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; No clipping is performed.
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; C near-callable as:
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;
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; void WritePixelX(int X, int Y, unsigned int PageBase, int Color);
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```nasm
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; Mode X (320x240, 256 colors) write pixel routine. Works on all VGAs.
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; No clipping is performed.
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; C near-callable as:
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;
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; void WritePixelX(int X, int Y, 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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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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X dw ? ;X coordinate of pixel to draw
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Y dw ? ;Y coordinate of pixel to draw
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PageBase dw ? ;base offset in display memory of page in
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; which to draw pixel
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Color dw ? ;color in which to draw pixel
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parms ends
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parms struc
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dw 2 dup (?) ;pushed BP and return address
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X dw ? ;X coordinate of pixel to draw
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Y dw ? ;Y coordinate of pixel to draw
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PageBase dw ? ;base offset in display memory of page in
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; which to draw pixel
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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 _WritePixelX
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_WritePixelX 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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.model small
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.code
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public _WritePixelX
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_WritePixelX 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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mov ax,SCREEN_WIDTH
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mul [bp+Y] ;offset of pixel's scan line in page
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mov bx,[bp+X]
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shr bx,1
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shr bx,1 ;X/4 = offset of pixel in scan line
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add bx,ax ;offset of pixel in page
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add bx,[bp+PageBase] ;offset of pixel in display memory
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mov ax,SCREEN_SEG
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mov es,ax ;point ES:BX to the pixel's address
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mov ax,SCREEN_WIDTH
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mul [bp+Y] ;offset of pixel's scan line in page
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mov bx,[bp+X]
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shr bx,1
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shr bx,1 ;X/4 = offset of pixel in scan line
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add bx,ax ;offset of pixel in page
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add bx,[bp+PageBase] ;offset of pixel in display memory
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mov ax,SCREEN_SEG
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mov es,ax ;point ES:BX to the pixel's address
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mov cl,byte ptr [bp+X]
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and cl,011b ;CL = pixel's plane
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mov ax,0100h + MAP_MASK ;AL = index in SC of Map Mask reg
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shl ah,cl ;set only the bit for the pixel's plane to 1
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mov dx,SC_INDEX ;set the Map Mask to enable only the
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out dx,ax ; pixel's plane
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mov cl,byte ptr [bp+X]
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and cl,011b ;CL = pixel's plane
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mov ax,0100h + MAP_MASK ;AL = index in SC of Map Mask reg
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shl ah,cl ;set only the bit for the pixel's plane to 1
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mov dx,SC_INDEX ;set the Map Mask to enable only the
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out dx,ax ; pixel's plane
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mov al,byte ptr [bp+Color]
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mov es:[bx],al ;draw the pixel in the desired color
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mov al,byte ptr [bp+Color]
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mov es:[bx],al ;draw the pixel in the desired color
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pop bp ;restore caller's stack frame
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ret
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_WritePixelX endp
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end
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pop bp ;restore caller's stack frame
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ret
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_WritePixelX endp
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end
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```
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**LISTING 47.3 L47-3.ASM**
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; Mode X (320x240, 256 colors) read pixel routine. Works on all VGAs.
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; No clipping is performed.
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; C near-callable as:
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;
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; unsigned int ReadPixelX(int X, int Y, unsigned int PageBase);
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```nasm
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; Mode X (320x240, 256 colors) read pixel routine. Works on all VGAs.
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; No clipping is performed.
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; C near-callable as:
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;
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; unsigned int ReadPixelX(int X, int Y, unsigned int PageBase);
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GC_INDEX equ 03ceh ;Graphics Controller Index
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READ_MAP equ 04h ;index in GC of the Read Map 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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X dw ? ;X coordinate of pixel to read
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Y dw ? ;Y coordinate of pixel to read
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PageBase dw ? ;base offset in display memory of page from
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; which to read pixel
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parms ends
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GC_INDEX equ 03ceh ;Graphics Controller Index
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READ_MAP equ 04h ;index in GC of the Read Map 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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X dw ? ;X coordinate of pixel to read
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Y dw ? ;Y coordinate of pixel to read
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PageBase dw ? ;base offset in display memory of page from
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; which to read pixel
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parms ends
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.model small
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.code
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public _ReadPixelX
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_ReadPixelX 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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.model small
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.code
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public _ReadPixelX
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_ReadPixelX 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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mov ax,SCREEN_WIDTH
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mul [bp+Y] ;offset of pixel's scan line in page
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mov bx,[bp+X]
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shr bx,1
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shr bx,1 ;X/4 = offset of pixel in scan line
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add bx,ax ;offset of pixel in page
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add bx,[bp+PageBase] ;offset of pixel in display memory
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mov ax,SCREEN_SEG
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mov es,ax ;point ES:BX to the pixel's address
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mov ax,SCREEN_WIDTH
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mul [bp+Y] ;offset of pixel's scan line in page
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mov bx,[bp+X]
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shr bx,1
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shr bx,1 ;X/4 = offset of pixel in scan line
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add bx,ax ;offset of pixel in page
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add bx,[bp+PageBase] ;offset of pixel in display memory
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mov ax,SCREEN_SEG
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mov es,ax ;point ES:BX to the pixel's address
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mov ah,byte ptr [bp+X]
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and ah,011b ;AH = pixel's plane
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mov al,READ_MAP ;AL = index in GC of the Read Map reg
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mov dx,GC_INDEX ;set the Read Map to read the pixel's
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out dx,ax ; plane
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mov ah,byte ptr [bp+X]
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and ah,011b ;AH = pixel's plane
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mov al,READ_MAP ;AL = index in GC of the Read Map reg
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mov dx,GC_INDEX ;set the Read Map to read the pixel's
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out dx,ax ; plane
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mov al,es:[bx] ;read the pixel's color
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sub ah,ah ;convert it to an unsigned int
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mov al,es:[bx] ;read the pixel's color
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sub ah,ah ;convert it to an unsigned int
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pop bp ;restore caller's stack frame
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ret
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_ReadPixelX endp
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end
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pop bp ;restore caller's stack frame
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ret
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_ReadPixelX endp
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end
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```
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