home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Gold Medal Software 3
/
Gold Medal Software - Volume 3 (Gold Medal) (1994).iso
/
graphics
/
3dvect30.arj
/
XSCALE.INC
< prev
Wrap
Text File
|
1993-11-18
|
37KB
|
783 lines
;=========================================================================
; XSCALE1.ASM by John A. Slagel, jas37876@uxa.cso.uiuc.edu
; This is some code to do bitmap scaling in VGA Mode X. It can scale a
; bitmap of any size down to 2 pixels wide, or up to thousands of pixels
; wide. It performs complete clipping, with only a small constant amount
; of time to clip, no matter how huge the image is. It draws column by
; column to reduce the number of plane switches, which are slow. The inner
; column loop has been optimized for no memory accesses, except to read or
; write a pixel. This uses MASM 5.1 features, and can be compiled in any
; memory model by changing the .MODEL line, but make sure that you always
; pass a far pointer to the bitmap data, regardless of memory model.
; C-callable as:
; void XSCALE1( int X, int Y, int DW, int DY,
; int SW, int SH, void far * Bitmap );
; X,Y are the upper left-hand coordinates of where to draw the bitmap.
; DW,DH are the width and height of the SCALEed bitmap
; SW,SH are the width and height of the source bitmap.
; Bitmap is a pointer to the bitmap bits.
;
; Routine has been modified for 32 bit protected mode by John McCarthy.
; John McCarthy thanks John A. Slagel for providing this code, and hopes
; John A. Slagel is not offended by the changes.
;
;==========================================================================
public draw_scale
public tdraw_scale
public tdraw_scale4
public xscale1
public xscale2
public xscale4
public repeat_bitmap
; uses edi esi, destx:word, desty:word,
; destwidth:word, destheight:word,
; sourcewidth:word, sourceheight:word,
; bitmap:far ptr
draw_scale:
mov bitmap,esi
mov destwidth,ax
mov destheight,bx
mov destx,cx
mov desty,dx
xscale1:
cmp destwidth, 2 ; if destination width is less than 2
jl done ; then don't draw it.
cmp destheight, 2 ; if destination height is less than 2
jl done ; then don't draw it.
mov ax, desty ; if it is completely below the
cmp ax, clipbt ; lower clip bondry,
jg done ; then don't draw it.
add ax, destheight ; if it is above clip boundries
dec ax ; then don't draw it.
cmp ax, cliptp
jl done
mov ax, destx ; if it is to the right of the
mov cx, cliprt ; right clip boundry
cmp ax, cliprt ; then don't draw it.
jg done
add ax, destwidth ; if it is completely to the left
dec ax ; of the left clip boundry,
cmp ax, cliplt ; then don't draw it.
jl done
mov esi, bitmap ; make esi point to bitmap data
lodsw ; get source x width
mov sourcewidth,ax
lodsw ; get source y height
mov sourceheight,ax
mov ax, destwidth ; clippedwidth is initially set to
mov clippedwidth, ax ; the requested dest width.
shl ax,1 ; initialize the x decision var
neg ax ; to be -2*destwidth
mov decisionx, ax ;
mov ax, destheight ; clippedheight is initially set to
mov clippedheight, ax ; the requested dest size.
shl ax,1 ; initialize the y decision var
neg ax ; to be -2*destheight
mov decisiony, ax ;
movsx eax, cliptp ; if y is below the top
mov edx, eax ; clipping boundry, then we don't
sub dx, desty ; need to clip the top, so we can
js s notopclip ; jump over the clipping stuff.
mov desty, ax ; this block performs clipping on the
sub clippedheight, dx ; top of the bitmap. i have heavily
movsx ecx, sourceheight ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destheight ; this: the decisiony var is updated
idiv ebx ; to start at the right clipped row.
movsx edx, sourcewidth ; y is moved to the top clip
imul edx, eax ; boundry. clippedheight is lowered since
add esi, edx ; we won't be drawing all the requested
imul eax, ebx ; rows. esi is changed to point over
sub ecx, eax ; the bitmap data that is clipped off.
sub ecx, ebx ;
shl ecx, 1 ;
mov decisiony, cx ; <end of top clipping block >
notopclip:
mov ax, desty ; if the bitmap doesn't extend over the
add ax, clippedheight ; bottom clipping boundry, then we
dec ax ; don't need to clip the bottom, so we
cmp ax, clipbt ; can jump over the bottom clip code.
jle s nobottomclip ;
mov ax, clipbt ; clip off the bottom by reducing the
sub ax, desty ; clippedheight so that the bitmap won't
inc ax ; extend over the lower clipping
mov clippedheight, ax ; boundry.
nobottomclip:
movsx eax, cliplt ; if x is to the left of the
mov edx, eax ; top clipping boundry, then we don't
sub dx, destx ; need to clip the left, so we can
js s noleftclip ; jump over the clipping stuff.
mov destx, ax ; this block performs clipping on the
sub clippedwidth, dx ; left of the bitmap. i have heavily
movsx ecx, sourcewidth ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destwidth ; this: the decisionx var is updated
idiv ebx ; to start at the right clipped column.
add esi, eax ; x is moved to the left clip
imul eax, ebx ; boundry. clippedwidth is reduced since
sub ecx, eax ; we won't be drawing all the requested
sub ecx, ebx ; cols. esi is changed to point over
shl ecx, 1 ; the bitmap data that is clipped off.
mov decisionx, cx ; <end of left clipping block >
noleftclip:
mov ax, destx ; if the bitmap doesn't extend over the
add ax, clippedwidth ; right clipping boundry, then we
dec ax ; don't need to clip the right, so we
cmp ax, cliprt ; can jump over the right clip code.
jle s noclipright ;
mov ax, cliprt ; clip off the right by reducing the
sub ax, destx ; clippedwidth so that the bitmap won't
inc ax ; extend over the right clipping
mov clippedwidth, ax ; boundry.
;calculate starting video address
noclipright:
movzx edi, desty ; we are going to set edi to start point
imul edi, xactual/4
movzx eax, destx ; the offset edi is
mov cx, ax ; calculated by:
shr ax, 2 ; di = y*80+x/2
add eax, current_page
add edi,eax ; edi is ready!
mov dx, sc_index+1 ; point the vga sequencer to the map
; mov al, map_mask ; mask register, so that we only need
; out dx, al ; to send out 1 byte per column.
; inc dx ; move to the sequencer's data register.
and cx, 3 ; calculate the starting plane. this is
mov al, 11h ; just:
shl al, cl ; plane = (11h << (x and 3))
out dx, al ; select the first plane.
movzx ecx, sourcewidth ; use cx for source width
mov xad, ecx
shl sourcewidth,1
align 16 ; since this point gets jumped to a lot,
; make sure that it is dword aligned.
rowloop:
push esi ; save the starting source index
push edi ; save the starting dest index
push ax ; save the current plane mask
push bp ; save the current base pointer
mov cx, clippedheight ; use al for row counter (0-239)
mov bx, decisiony ; use bx for decision variable
mov dx, sourceheight ; use dx for source height * 2
shl dx, 1
mov bp, destheight ; use bp for dest height * 2
shl bp, 1
mov ah, [esi] ; get the first source pixel
align 4 ; common jump point... align for speed.
columnloop:
mov [edi], ah ; draw a pixel
dec cx ; decrement line counter
jz s donewithcol ; see if we're done with this column
add edi, xactual/4 ; go on to the next screen row
add bx, dx ; increment the decision variable
js s columnloop ; draw this source pixel again
incsourcerow:
add esi, xad ; move to the next source pixel
sub bx, bp ; decrement the decision variable
jns s incsourcerow ; see if we need to skip another source pixel
mov ah, [esi] ; get the next source pixel
jmp s columnloop ; start drawing this pixel
donewithcol:
pop bp ; restore bp to access variables
pop ax ; restore al = plane mask
pop edi ; restore di to top row of screen
pop esi ; restore si to top row of source bits
rol al, 1 ; move to next plane
adc edi, 0 ; go on to next screen column
mov dx, sc_data ; tell the vga what column we're in
out dx, al ; by updating the map mask register
mov bx, decisionx ; use bx for the x decision variable
add bx, sourcewidth ; increment the x decision variable
js s nextcol ; jump if we're still in the same source col.
mov dx, destwidth ; dx = w * 2
shl dx, 1
incsourcecol:
inc esi ; move to next source column
sub bx, dx ; decrement x decision variable
jns s incsourcecol ; see if we skip another source column
nextcol:
mov decisionx, bx ; free up bx for colloop
dec clippedwidth ; if we're not at last column
jnz rowloop ; then do another column
done:
ret ; we're done!
; draw transparent bitmap. any bytes that = 0 are skipped
tdraw_scale:
mov bitmap,esi
mov destwidth,ax
mov destheight,bx
mov destx,cx
mov desty,dx
xscale2:
cmp destwidth, 2 ; if destination width is less than 2
jl s done ; then don't draw it.
cmp destheight, 2 ; if destination height is less than 2
jl s done ; then don't draw it.
mov ax, desty ; if it is completely below the
cmp ax, clipbt ; lower clip bondry,
jg s done ; then don't draw it.
add ax, destheight ; if it is above clip boundries
dec ax ; then don't draw it.
cmp ax, cliptp
jl s done
mov ax, destx ; if it is to the right of the
mov cx, cliprt ; right clip boundry
cmp ax, cliprt ; then don't draw it.
jg s done
add ax, destwidth ; if it is completely to the left
dec ax ; of the left clip boundry,
cmp ax, cliplt ; then don't draw it.
jl s done
mov esi, bitmap ; make esi point to bitmap data
lodsw ; get source x width
mov sourcewidth,ax
lodsw ; get source y height
mov sourceheight,ax
mov ax, destwidth ; clippedwidth is initially set to
mov clippedwidth, ax ; the requested dest width.
shl ax,1 ; initialize the x decision var
neg ax ; to be -2*destwidth
mov decisionx, ax ;
mov ax, destheight ; clippedheight is initially set to
mov clippedheight, ax ; the requested dest size.
shl ax,1 ; initialize the y decision var
neg ax ; to be -2*destheight
mov decisiony, ax ;
movsx eax, cliptp ; if y is below the top
mov edx, eax ; clipping boundry, then we don't
sub dx, desty ; need to clip the top, so we can
js s notopclip2 ; jump over the clipping stuff.
mov desty, ax ; this block performs clipping on the
sub clippedheight, dx ; top of the bitmap. i have heavily
movsx ecx, sourceheight ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destheight ; this: the decisiony var is updated
idiv ebx ; to start at the right clipped row.
movsx edx, sourcewidth ; y is moved to the top clip
imul edx, eax ; boundry. clippedheight is lowered since
add esi, edx ; we won't be drawing all the requested
imul eax, ebx ; rows. esi is changed to point over
sub ecx, eax ; the bitmap data that is clipped off.
sub ecx, ebx ;
shl ecx, 1 ;
mov decisiony, cx ; <end of top clipping block >
notopclip2:
mov ax, desty ; if the bitmap doesn't extend over the
add ax, clippedheight ; bottom clipping boundry, then we
dec ax ; don't need to clip the bottom, so we
cmp ax, clipbt ; can jump over the bottom clip code.
jle s nobottomclip2
mov ax, clipbt ; clip off the bottom by reducing the
sub ax, desty ; clippedheight so that the bitmap won't
inc ax ; extend over the lower clipping
mov clippedheight, ax ; boundry.
nobottomclip2:
movsx eax, cliplt ; if x is to the left of the
mov edx, eax ; top clipping boundry, then we don't
sub dx, destx ; need to clip the left, so we can
js s noleftclip2 ; jump over the clipping stuff.
mov destx, ax ; this block performs clipping on the
sub clippedwidth, dx ; left of the bitmap. i have heavily
movsx ecx, sourcewidth ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destwidth ; this: the decisionx var is updated
idiv ebx ; to start at the right clipped column.
add esi, eax ; x is moved to the left clip
imul eax, ebx ; boundry. clippedwidth is reduced since
sub ecx, eax ; we won't be drawing all the requested
sub ecx, ebx ; cols. esi is changed to point over
shl ecx, 1 ; the bitmap data that is clipped off.
mov decisionx, cx ; <end of left clipping block >
noleftclip2:
mov ax, destx ; if the bitmap doesn't extend over the
add ax, clippedwidth ; right clipping boundry, then we
dec ax ; don't need to clip the right, so we
cmp ax, cliprt ; can jump over the right clip code.
jle s noclipright2
mov ax, cliprt ; clip off the right by reducing the
sub ax, destx ; clippedwidth so that the bitmap won't
inc ax ; extend over the right clipping
mov clippedwidth, ax ; boundry.
;calculate starting video address
noclipright2:
movsx edi, desty ; we are going to set edi to start point
imul edi, xactual/4
movsx eax, destx ; the offset edi is
mov cx, ax ; calculated by:
shr eax, 2 ; edi = y*80+x/2
add eax, current_page
add edi,eax ; edi is ready!
mov dx, sc_index+1 ; point the vga sequencer to the map
; mov al, map_mask ; mask register, so that we only need
; out dx, al ; to send out 1 byte per column.
; inc dx ; move to the sequencer's data register.
and cx, 3 ; calculate the starting plane. this is
mov al, 11h ; just:
shl al, cl ; plane = (11h << (x and 3))
out dx, al ; select the first plane.
movzx ecx, sourcewidth ; use cx for source width
mov xad, ecx
shl sourcewidth,1
align 16 ; since this point gets jumped to a lot,
; make sure that it is dword aligned.
rowloop2:
push esi ; save the starting source index
push edi ; save the starting dest index
push ax ; save the current plane mask
push bp ; save the current base pointer
mov cx, clippedheight ; use al for row counter (0-239)
mov bx, decisiony ; use bx for decision variable
mov dx, sourceheight ; use dx for source height * 2
shl dx, 1
mov bp, destheight ; use bp for dest height * 2
shl bp, 1
mov ah, [esi] ; get the first source pixel
or ah,ah
jz s null_loop ; if zero, perform null loop
align 4 ; common jump point... align for speed.
columnloop2:
mov [edi], ah ; draw a pixel
dec cx ; decrement line counter
jz s donewithcol2 ; see if we're done with this column
add edi, xactual/4 ; go on to the next screen row
add bx, dx ; increment the decision variable
js s columnloop2 ; draw this source pixel again
incsourcerow2:
add esi, xad ; move to the next source pixel
sub bx, bp ; decrement the decision variable
jns s incsourcerow2 ; see if we need to skip another source pixel
mov ah, [esi] ; get the next source pixel
cmp ah,0
jz s null_loop
jmp s columnloop2 ; start drawing this pixel
donewithcol2:
pop bp ; restore bp to access variables
pop ax ; restore al = plane mask
pop edi ; restore di to top row of screen
pop esi ; restore si to top row of source bits
rol al, 1 ; move to next plane
adc edi, 0 ; go on to next screen column
mov dx, sc_data ; tell the vga what column we're in
out dx, al ; by updating the map mask register
mov bx, decisionx ; use bx for the x decision variable
add bx, sourcewidth ; increment the x decision variable
js s nextcol2 ; jump if we're still in the same source col.
mov dx, destwidth ; dx = w * 2
shl dx, 1
incsourcecol2:
inc esi ; move to next source column
sub bx, dx ; decrement x decision variable
jns s incsourcecol2 ; see if we skip another source column
nextcol2:
mov decisionx, bx ; free up bx for colloop
dec clippedwidth ; if we're not at last column
jnz rowloop2 ; then do another column
done2:
ret ; we're done!
align 16 ; common jump point... align for speed.
null_loop:
dec cx ; decrement line counter
jz s donewithcol2 ; see if we're done with this column
add edi, xactual/4 ; go on to the next screen row
add bx, dx ; increment the decision variable
js s null_loop ; perform more increments
jmp s incsourcerow2
; draw repeated bit map. good for backgrounds in menus and title screens.
; routine is NOT intended for animation because it is slow. uses scale routine
; because scale routine clips bitmaps. sloppy routine just draws all over the
; place and lets the scale clip borders handle the rest.
;
; repeat_bitmap (seg bitmap, x1%, y1%, x2%, y2%)
;
; remember: first two words of bitmap define width and height
rb_stack struc
rb_wide dw ? ; height and width of bitmap
rb_height dw ?
rb_curx dw ? ; current bitmap location
rb_cury dw ?
rb_oldy2 dw ? ; old cliping borders save
rb_oldx2 dw ?
rb_oldy1 dw ?
rb_oldx1 dw ?
dd ?x3 ; edi, esi, ebp
dd ? ; caller
rb_y2 dw ? ; y2
rb_x2 dw ? ; x2
rb_y1 dw ? ; y1
rb_x1 dw ? ; x1
rb_bitmap dd ? ; offset to bitmap
rb_stack ends
repeat_bitmap:
push ebp esi edi ; preserve important registers
sub esp, 16 ; allocate workspace
mov ebp, esp ; set up stack frame
mov ax,cliplt ; save old borders just in case
mov [ebp].rb_oldx1,ax
mov ax,cliprt
mov [ebp].rb_oldx2,ax
mov ax,cliptp
mov [ebp].rb_oldy1,ax
mov ax,clipbt
mov [ebp].rb_oldy2,ax
mov x1,4
mov ax,[ebp].rb_x1 ; set new borders for clipping
mov cliplt,ax
mov ax,[ebp].rb_x2
mov cliprt,ax
mov ax,[ebp].rb_y1
mov cliptp,ax
mov ax,[ebp].rb_y2
mov clipbt,ax
mov [ebp].rb_curx,0 ; we could start at x1,y1 but this
mov [ebp].rb_cury,0 ; will make offset backgrounds
mov esi,[ebp].rb_bitmap
mov bitmap,esi
lodsw ; set destination width same as original
mov [ebp].rb_wide,ax
lodsw
mov [ebp].rb_height,ax
nextline:
mov ax,[ebp].rb_wide
mov destwidth,ax
mov ax,[ebp].rb_height
mov destheight,ax
mov ax,[ebp].rb_curx
mov destx,ax
mov ax,[ebp].rb_cury
mov desty,ax
push ebp
call xscale2 ; draw a transparent bitmap
pop ebp
mov ax,[ebp].rb_curx
add ax,[ebp].rb_wide
mov [ebp].rb_curx,ax
cmp ax,[ebp].rb_x2
jle s nextline
mov [ebp].rb_curx,0
mov ax,[ebp].rb_cury
add ax,[ebp].rb_height
mov [ebp].rb_cury,ax
cmp ax,[ebp].rb_y2
jle s nextline
mov ax,[ebp].rb_oldx1
mov cliplt,ax
mov ax,[ebp].rb_oldx2
mov cliprt,ax
mov ax,[ebp].rb_oldy1
mov cliptp,ax
mov ax,[ebp].rb_oldy2
mov clipbt,ax
add esp, 16
pop edi esi ebp
ret 12
; draw transparent bitmap using 1/4 xmode method. - draws every 4 pixels alike.
; great for explosions/smoke where the bitmap does not have to be very
; accuratly drawn - much faster
done4: ret
tdraw_scale4:
mov bitmap,esi
mov destwidth,ax
mov destheight,bx
mov destx,cx
mov desty,dx
xscale4:
cmp destwidth, 2 ; if destination width is less than 2
jl s done4 ; then don't draw it.
cmp destheight, 2 ; if destination height is less than 2
jl s done4 ; then don't draw it.
mov ax, desty ; if it is completely below the
cmp ax, clipbt ; lower clip bondry,
jg s done4 ; then don't draw it.
add ax, destheight ; if it is above clip boundries
dec ax ; then don't draw it.
cmp ax, cliptp
jl s done4
mov ax, destx ; if it is to the right of the
mov cx, cliprt ; right clip boundry
cmp ax, cliprt ; then don't draw it.
jg s done4
add ax, destwidth ; if it is completely to the left
dec ax ; of the left clip boundry,
cmp ax, cliplt ; then don't draw it.
jl s done4
mov esi, bitmap ; make esi point to bitmap data
lodsw ; get source x width
mov sourcewidth,ax
lodsw ; get source y height
mov sourceheight,ax
mov ax, destwidth ; clippedwidth is initially set to
mov clippedwidth, ax ; the requested dest width.
shl ax,1 ; initialize the x decision var
neg ax ; to be -2*destwidth
mov decisionx, ax ;
mov ax, destheight ; clippedheight is initially set to
mov clippedheight, ax ; the requested dest size.
shl ax,1 ; initialize the y decision var
neg ax ; to be -2*destheight
mov decisiony, ax ;
movsx eax, cliptp ; if y is below the top
mov edx, eax ; clipping boundry, then we don't
sub dx, desty ; need to clip the top, so we can
js s notopclip4 ; jump over the clipping stuff.
mov desty, ax ; this block performs clipping on the
sub clippedheight, dx ; top of the bitmap. i have heavily
movsx ecx, sourceheight ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destheight ; this: the decisiony var is updated
idiv ebx ; to start at the right clipped row.
movsx edx, sourcewidth ; y is moved to the top clip
imul edx, eax ; boundry. clippedheight is lowered since
add esi, edx ; we won't be drawing all the requested
imul eax, ebx ; rows. esi is changed to point over
sub ecx, eax ; the bitmap data that is clipped off.
sub ecx, ebx ;
shl ecx, 1 ;
mov decisiony, cx ; <end of top clipping block >
notopclip4:
mov ax, desty ; if the bitmap doesn't extend over the
add ax, clippedheight ; bottom clipping boundry, then we
dec ax ; don't need to clip the bottom, so we
cmp ax, clipbt ; can jump over the bottom clip code.
jle s nobottomclip4
mov ax, clipbt ; clip off the bottom by reducing the
sub ax, desty ; clippedheight so that the bitmap won't
inc ax ; extend over the lower clipping
mov clippedheight, ax ; boundry.
nobottomclip4:
movsx eax, cliplt ; if x is to the left of the
mov edx, eax ; top clipping boundry, then we don't
sub dx, destx ; need to clip the left, so we can
js s noleftclip4 ; jump over the clipping stuff.
mov destx, ax ; this block performs clipping on the
sub clippedwidth, dx ; left of the bitmap. i have heavily
movsx ecx, sourcewidth ; optimized this block to use only 4
imul ecx, edx ; 32-bit registers, so i'm not even
mov eax, ecx ; gonna try to explain what it's doing.
cdq ; but i can tell you what results from
movsx ebx, destwidth ; this: the decisionx var is updated
idiv ebx ; to start at the right clipped column.
add esi, eax ; x is moved to the left clip
imul eax, ebx ; boundry. clippedwidth is reduced since
sub ecx, eax ; we won't be drawing all the requested
sub ecx, ebx ; cols. esi is changed to point over
shl ecx, 1 ; the bitmap data that is clipped off.
mov decisionx, cx ; <end of left clipping block >
noleftclip4:
mov ax, destx ; if the bitmap doesn't extend over the
add ax, clippedwidth ; right clipping boundry, then we
dec ax ; don't need to clip the right, so we
cmp ax, cliprt ; can jump over the right clip code.
jle s noclipright4
mov ax, cliprt ; clip off the right by reducing the
sub ax, destx ; clippedwidth so that the bitmap won't
inc ax ; extend over the right clipping
mov clippedwidth, ax ; boundry.
;calculate starting video address
noclipright4:
movsx edi, desty ; we are going to set edi to start point
imul edi, xactual/4
movsx eax, destx ; the offset edi is
mov cx, ax ; calculated by:
shr eax, 2 ; edi = y*80+x/2
add eax, current_page
add edi,eax ; edi is ready!
mov dx, sc_index+1 ; point the vga sequencer to the map
; mov al, map_mask ; mask register, so that we only need
; out dx, al ; to send out 1 byte per column.
; inc dx ; move to the sequencer's data register.
mov al, all_planes
out dx, al ; select the first plane.
movzx ecx, sourcewidth ; use cx for source width
mov xad, ecx
shl sourcewidth,1+2 ; 4 times as fast
shr clippedwidth,2 ; 1/4 of the plots
cmp clippedwidth,0 ; check if <4 wide
jne s rowloop4
inc clippedwidth
align 16 ; since this point gets jumped to a lot,
; make sure that it is dword aligned.
rowloop4:
push esi ; save the starting source index
push edi ; save the starting dest index
push bp ; save the current base pointer
mov cx, clippedheight ; use al for row counter (0-239)
mov bx, decisiony ; use bx for decision variable
mov dx, sourceheight ; use dx for source height * 2
shl dx, 1
mov bp, destheight ; use bp for dest height * 2
shl bp, 1
mov ah, [esi] ; get the first source pixel
or ah,ah
jz s null_loop4 ; if zero, perform null loop
align 4 ; common jump point... align for speed.
columnloop4:
mov [edi], ah ; draw a pixel
dec cx ; decrement line counter
jz s donewithcol4 ; see if we're done with this column
add edi, xactual/4 ; go on to the next screen row
add bx, dx ; increment the decision variable
js s columnloop4 ; draw this source pixel again
incsourcerow4:
add esi, xad ; move to the next source pixel
sub bx, bp ; decrement the decision variable
jns s incsourcerow4 ; see if we need to skip another source pixel
mov ah, [esi] ; get the next source pixel
or ah,ah
jz s null_loop4
jmp s columnloop4 ; start drawing this pixel
donewithcol4:
pop bp ; restore bp to access variables
pop edi ; restore di to top row of screen
pop esi ; restore si to top row of source bits
add edi, 1 ; go on to next screen column
mov bx, decisionx ; use bx for the x decision variable
add bx, sourcewidth ; increment the x decision variable
mov dx, destwidth ; dx = w * 2
shl dx, 1
incsourcecol4:
inc esi ; move to next source column
sub bx, dx ; decrement x decision variable
jns s incsourcecol4 ; see if we skip another source column
nextcol4:
mov decisionx, bx ; free up bx for colloop
dec clippedwidth ; if we're not at last column
jnz rowloop4 ; then do another column
ret ; we're done!
align 16 ; common jump point... align for speed.
null_loop4:
dec cx ; decrement line counter
jz s donewithcol4 ; see if we're done with this column
add edi, xactual/4 ; go on to the next screen row
add bx, dx ; increment the decision variable
js s null_loop4 ; perform more increments
jmp s incsourcerow4
