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MEM2SC.ASM
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Assembly Source File
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1995-02-21
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6KB
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128 lines
.386p
locals
include w.inc
; 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. 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
parms struc
dd 2 dup (?) ;pushed BP and return address
SourceStartX dd ? ;X coordinate of upper left corner of source
SourceStartY dd ? ;Y coordinate of upper left corner of source
SourceEndX dd ? ;X coordinate of lower right corner of source
; (the row at EndX is not copied)
SourceEndY dd ? ;Y coordinate of lower right corner of source
; (the column at EndY is not copied)
DestStartX dd ? ;X coordinate of upper left corner of dest
DestStartY dd ? ;Y coordinate of upper left corner of dest
SourcePtr dd ? ;pointer in DS to start of bitmap in which
; source resides
DestPageBase dd ? ;base offset in display memory of page in
; which dest resides
SourceBitmapWidth dd ? ;# of pixels across source bitmap
DestBitmapWidth dd ? ;# of pixels across dest bitmap
; (must be a multiple of 4)
parms ends
RectWidth equ -4 ;local storage for width of rectangle
LeftMask equ -6 ;local storage for left rect edge plane mask
STACK_FRAME_SIZE equ 6
@dseg
extrn SCREEN_SEG:dword
ends
@cseg
public _CopySystemToScreenX
_CopySystemToScreenX proc near
push ebp ;preserve caller's stack frame
mov ebp,esp ;point to local stack frame
sub esp,STACK_FRAME_SIZE ;allocate space for local vars
push esi ;preserve caller's register variables
push edi
push ebx
cld
mov eax,[ebp+SourceBitmapWidth]
mul [ebp+SourceStartY] ;top source rect scan line
add eax,[ebp+SourceStartX]
add eax,[ebp+SourcePtr] ;offset of first source rect pixel
mov esi,eax ; in DS:ESI
mov eax, [ebp+DestBitmapWidth]
shr eax,2 ;convert to width in addresses
mov [ebp+DestBitmapWidth],eax ;remember address width
mul [ebp+DestStartY] ;top dest rect scan line
mov edi, [ebp+DestStartX] ; clear hi(edi)
mov ecx,edi
shr edi,2 ;X/4 = offset of first dest rect pixel in scan line
add edi,eax ;offset of first dest rect pixel in page
add edi,[ebp+DestPageBase] ;offset of first dest rect pixel
; in display memory
add edi,[SCREEN_SEG] ;make mem ptr now
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 [ebp+LeftMask],al ; in each nibble to 1
mov ecx,[ebp+SourceEndX] ;calculate # of pixels across
sub ecx,[ebp+SourceStartX] ; rect
jle CopyDone ;skip if 0 or negative width
mov [ebp+RectWidth],ecx
mov ebx,[ebp+SourceEndY]
sub ebx,[ebp+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,[ebp+LeftMask]
mov ecx,[ebp+RectWidth]
push esi ;remember the start offset in the source
push edi ;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 edi ;retrieve the dest start offset
add edi,[ebp+DestBitmapWidth] ;point to the start of the
; next scan line of the dest
pop esi ;retrieve the source start offset
add esi,[ebp+SourceBitmapWidth] ;point to the start of the
; next scan line of the source
dec ebx ;count down scan lines
jnz CopyRowsLoop
CopyDone:
pop ebx
pop edi ;restore caller's register variables
pop esi
mov esp,ebp ;discard storage for local variables
pop ebp ;restore caller's stack frame
ret
_CopySystemToScreenX endp
ends
end