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<HTML>
<HEAD>
<META name=vsisbn content="1576101746">
<META name=vstitle content="Michael Abrash's Graphics Programming Black Book, Special Edition">
<META name=vsauthor content="Michael Abrash">
<META name=vspublisher content="The Coriolis Group">
<META name=vspubdate content="07/01/97">
<META name=vscategory content="Web and Software Development: Game Development,Web and Software Development: Graphics and Multimedia Development">
<TITLE>Michael Abrash's Graphics Programming Black Book Special Edition: Mode X Marks the Latch</TITLE>
<!-- HEADER -->
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<!--ISBN=1576101746//-->
<!--TITLE=Michael Abrash's Graphics Programming Black Book Special Edition//-->
<!--AUTHOR=Michael Abrash//-->
<!--PUBLISHER=The Coriolis Group, Inc.//-->
<!--CHAPTER=48//-->
<!--PAGES=905-908//-->
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<CENTER>
<TABLE BORDER>
<TR>
<TD><A HREF="48-03.html">Previous</A></TD>
<TD><A HREF="index.html">Table of Contents</A></TD>
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<P><BR></P>
<P><B>LISTING 48.3 L48-3.ASM</B></P>
<!-- CODE //-->
<PRE>
; Mode X (320x240, 256 colors) display memory to display memory copy
; routine. Left edge of source rectangle modulo 4 must equal left edge
; of destination rectangle modulo 4. Works on all VGAs. Uses approach
; of reading 4 pixels at a time from the source into the latches, then
; writing the latches to the destination. Copies up to but not
; including the column at SourceEndX and the row at SourceEndY. No
; clipping is performed. Results are not guaranteed if the source and
; destination overlap. C near-callable as:
;
; void CopyScreenToScreenX(int SourceStartX, int SourceStartY,
; int SourceEndX, int SourceEndY, int DestStartX,
; int DestStartY, unsigned int SourcePageBase,
; 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
GC_INDEX equ 03ceh ;Graphics Controller Index register port
BIT_MASK equ 08h ;index in GC of Bit 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 SourceEndX is not copied)
SourceEndY dw ? ;Y coordinate of lower-right corner of source
; (the column at SourceEndY is not copied)
DestStartX dw ? ;X coordinate of upper-left corner of dest
DestStartY dw ? ;Y coordinate of upper-left corner of dest
SourcePageBase dw ? ;base offset in display memory of page in
; which source resides
DestPageBase dw ? ;base offset in display memory of page in
; which dest resides
SourceBitmapWidth dw ? ;# of pixels across source bitmap
; (must be a multiple of 4)
DestBitmapWidth dw ? ;# of pixels across dest bitmap
; (must be a multiple of 4)
parms ends
SourceNextScanOffset equ -2 ;local storage for distance from end of
; one source scan line to start of next
DestNextScanOffset equ -4 ;local storage for distance from end of
; one dest scan line to start of next
RectAddrWidth equ -6 ;local storage for address width of rectangle
Height equ -8;local storage for height of rectangle
STACK_FRAME_SIZE equ 8
.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 _CopyScreenToScreenX
_CopyScreenToScreenX proc near
push bp ;preserve caller&#146;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&#146;s register variables
push di
push ds
cld
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,SCREEN_SEG ;point ES to display memory
mov es,ax
mov ax,[bp+DestBitmapWidth]
shr ax,1 ;convert to width in addresses
shr ax,1
mul [bp+DestStartY] ;top dest rect scan line
mov di,[bp+DestStartX]
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
mov ax,[bp+SourceBitmapWidth]
shr ax,1 ;convert to width in addresses
shr ax,1
mul [bp+SourceStartY] ;top source rect scan line
mov si,[bp+SourceStartX]
mov bx,si
shr si,1 ;X/4 = offset of first source rect pixel in
shr si,1 ; scan line
add si,ax ;offset of first source rect pixel in page
add si,[bp+SourcePageBase] ;offset of first source rect
; pixel in display memory
and bx,0003h ;look up left edge plane mask
mov ah,LeftClipPlaneMask[bx] ; to clip
mov bx,[bp+SourceEndX]
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+SourceEndX] ;calculate # of addresses across
mov ax,[bp+SourceStartX] ; rect
cmp cx,ax
jle CopyDone ;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 copy - 1
jnz MasksSet ;there&#146;s more than one address to draw
and bh,bl ;there&#146;s only one address, so combine the
; left- and right-edge clip masks
MasksSet:
mov ax,[bp+SourceEndY]
sub ax,[bp+SourceStartY] ;AX = height of rectangle
jle CopyDone ;skip if 0 or negative height
mov [bp+Height],ax
mov ax,[bp+DestBitmapWidth]
shr ax,1 ;convert to width in addresses
shr ax,1
sub ax,cx ;distance from end of one dest scan line to
dec ax ; start of next
mov [bp+DestNextScanOffset],ax
mov ax,[bp+SourceBitmapWidth]
shr ax,1 ;convert to width in addresses
shr ax,1
sub ax,cx ;distance from end of one source scan line to
dec ax ; start of next
mov [bp+SourceNextScanOffset],ax
mov [bp+RectAddrWidth],cx ;remember width in addresses - 1
;----------------------BUG FIX
mov dx,SC_INDEX
mov al,MAP_MASK
out dx,al ;point SC Index reg to Map Mask
inc dx ;point to SC Data reg
;----------------------BUG FIX
mov ax,es ;DS=ES=screen segment for MOVS
mov ds,ax
CopyRowsLoop:
mov cx,[bp+RectAddrWidth] ;width across - 1
mov al,bh ;put left-edge clip mask in AL
out dx,al ;set the left-edge plane (clip) mask
movsb ;copy the left edge (pixels go through
; latches)
dec cx ;count off left edge address
js CopyLoopBottom ;that&#146;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 movsb ;draw the middle addresses four pixels apiece
; (pixels copied through latches)
DoRightEdge:
mov al,bl ;put right-edge clip mask in AL
out dx,al ;set the right-edge plane (clip) mask
movsb ;draw the right edge (pixels copied through
; latches)
CopyLoopBottom:
add si,[bp+SourceNextScanOffset] ;point to the start of
add di,[bp+DestNextScanOffset] ; next source &amp dest lines
dec word ptr [bp+Height] ;count down scan lines
jnz CopyRowsLoop
CopyDone:
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 ds
pop di ;restore caller&#146;s register variables
pop si
mov sp,bp ;discard storage for local variables
pop bp ;restore caller&#146;s stack frame
ret
_CopyScreenToScreenX endp
end
</PRE>
<!-- END CODE //-->
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<font face="Verdana,sans-serif" size="1">Graphics Programming Black Book &copy; 2001 Michael Abrash</font>
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