_GRAPHICS PROGRAMMING COLUMN_
by Michael Abrash
[LISTING ONE]
; Mode X (320x240, 256 colors) mode set routine. Works on all VGAs.
; C near-callable as:
; void Set320x240Mode(void);
; Tested with TASM 2.0.
; Modified from public-domain mode set code by John Bridges.
SC_INDEX equ 03c4h ;Sequence Controller Index
CRTC_INDEX equ 03d4h ;CRT Controller Index
MISC_OUTPUT equ 03c2h ;Miscellaneous Output register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
.model small
.data
; Index/data pairs for CRT Controller registers that differ between
; mode 13h and mode X.
CRTParms label word
dw 00d06h ;vertical total
dw 03e07h ;overflow (bit 8 of vertical counts)
dw 04109h ;cell height (2 to double-scan)
dw 0ea10h ;v sync start
dw 0ac11h ;v sync end and protect cr0-cr7
dw 0df12h ;vertical displayed
dw 00014h ;turn off dword mode
dw 0e715h ;v blank start
dw 00616h ;v blank end
dw 0e317h ;turn on byte mode
CRT_PARM_LENGTH equ (($-CRTParms)/2)
.code
public _Set320x240Mode
_Set320x240Mode proc near
push bp ;preserve caller's stack frame
push si ;preserve C register vars
push di ; (don't count on BIOS preserving anything)
mov ax,13h ;let the BIOS set standard 256-color
int 10h ; mode (320x200 linear)
mov dx,SC_INDEX
mov ax,0604h
out dx,ax ;disable chain4 mode
mov ax,0100h
out dx,ax ;synchronous reset while switching clocks
mov dx,MISC_OUTPUT
mov al,0e7h
out dx,al ;select 28 MHz dot clock & 60 Hz scanning rate
mov dx,SC_INDEX
mov ax,0300h
out dx,ax ;undo reset (restart sequencer)
mov dx,CRTC_INDEX ;reprogram the CRT Controller
mov al,11h ;VSync End reg contains register write
out dx,al ; protect bit
inc dx ;CRT Controller Data register
in al,dx ;get current VSync End register setting
and al,7fh ;remove write protect on various
out dx,al ; CRTC registers
dec dx ;CRT Controller Index
cld
mov si,offset CRTParms ;point to CRT parameter table
mov cx,CRT_PARM_LENGTH ;# of table entries
SetCRTParmsLoop:
lodsw ;get the next CRT Index/Data pair
out dx,ax ;set the next CRT Index/Data pair
loop SetCRTParmsLoop
mov dx,SC_INDEX
mov ax,0f02h
out dx,ax ;enable writes to all four planes
mov ax,SCREEN_SEG ;now clear all display memory, 8 pixels
mov es,ax ; at a time
sub di,di ;point ES:DI to display memory
sub ax,ax ;clear to zero-value pixels
mov cx,8000h ;# of words in display memory
rep stosw ;clear all of display memory
pop di ;restore C register vars
pop si
pop bp ;restore caller's stack frame
ret
_Set320x240Mode endp
end
[LISTING TWO]
; Mode X (320x240, 256 colors) write pixel routine. Works on all VGAs.
; No clipping is performed.
; C near-callable as:
; void WritePixelX(int X, int Y, unsigned int PageBase, int Color);
SC_INDEX equ 03c4h ;Sequence Controller Index
MAP_MASK equ 02h ;index in SC of Map Mask register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
; to the next
parms struc
dw 2 dup (?) ;pushed BP and return address
X dw ? ;X coordinate of pixel to draw
Y dw ? ;Y coordinate of pixel to draw
PageBase dw ? ;base offset in display memory of page in
; which to draw pixel
Color dw ? ;color in which to draw pixel
parms ends
.model small
.code
public _WritePixelX
_WritePixelX proc near
push bp ;preserve caller's stack frame
mov bp,sp ;point to local stack frame
mov ax,SCREEN_WIDTH
mul [bp+Y] ;offset of pixel's scan line in page
mov bx,[bp+X]
shr bx,1
shr bx,1 ;X/4 = offset of pixel in scan line
add bx,ax ;offset of pixel in page
add bx,[bp+PageBase] ;offset of pixel in display memory
mov ax,SCREEN_SEG
mov es,ax ;point ES:BX to the pixel's address
mov cl,byte ptr [bp+X]
and cl,011b ;CL = pixel's plane
mov ax,0100h + MAP_MASK ;AL = index in SC of Map Mask reg
shl ah,cl ;set only the bit for the pixel's plane to 1
mov dx,SC_INDEX ;set the Map Mask to enable only the
out dx,ax ; pixel's plane
mov al,byte ptr [bp+Color]
mov es:[bx],al ;draw the pixel in the desired color
pop bp ;restore caller's stack frame
ret
_WritePixelX endp
end
[LISTING THREE]
; Mode X (320x240, 256 colors) read pixel routine. Works on all VGAs.
; No clipping is performed.
; C near-callable as:
; unsigned int ReadPixelX(int X, int Y, unsigned int PageBase);
GC_INDEX equ 03ceh ;Graphics Controller Index
READ_MAP equ 04h ;index in GC of the Read Map register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
; to the next
parms struc
dw 2 dup (?) ;pushed BP and return address
X dw ? ;X coordinate of pixel to read
Y dw ? ;Y coordinate of pixel to read
PageBase dw ? ;base offset in display memory of page from
; which to read pixel
parms ends
.model small
.code
public _ReadPixelX
_ReadPixelX proc near
push bp ;preserve caller's stack frame
mov bp,sp ;point to local stack frame
mov ax,SCREEN_WIDTH
mul [bp+Y] ;offset of pixel's scan line in page
mov bx,[bp+X]
shr bx,1
shr bx,1 ;X/4 = offset of pixel in scan line
add bx,ax ;offset of pixel in page
add bx,[bp+PageBase] ;offset of pixel in display memory
mov ax,SCREEN_SEG
mov es,ax ;point ES:BX to the pixel's address
mov ah,byte ptr [bp+X]
and ah,011b ;AH = pixel's plane
mov al,READ_MAP ;AL = index in GC of the Read Map reg
mov dx,GC_INDEX ;set the Read Map to read the pixel's
out dx,ax ; plane
mov al,es:[bx] ;read the pixel's color
sub ah,ah ;convert it to an unsigned int
pop bp ;restore caller's stack frame
ret
_ReadPixelX endp
end
[LISTING FOUR]
; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
; VGAs. Uses slow approach that selects the plane explicitly for each
; pixel. Fills up to but not including the column at EndX and the row
; at EndY. No clipping is performed.
; C near-callable as:
; void FillRectangleX(int StartX, int StartY, int EndX, int EndY,
; unsigned int PageBase, int Color);
SC_INDEX equ 03c4h ;Sequence Controller Index
MAP_MASK equ 02h ;index in SC of Map Mask register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
; to the next
parms struc
dw 2 dup (?) ;pushed BP and return address
StartX dw ? ;X coordinate of upper left corner of rect
StartY dw ? ;Y coordinate of upper left corner of rect
EndX dw ? ;X coordinate of lower right corner of rect
; (the row at EndX is not filled)
EndY dw ? ;Y coordinate of lower right corner of rect
; (the column at EndY is not filled)
PageBase dw ? ;base offset in display memory of page in
; which to fill rectangle
Color dw ? ;color in which to draw pixel
parms ends
.model small
.code
public _FillRectangleX
_FillRectangleX proc near
push bp ;preserve caller's stack frame
mov bp,sp ;point to local stack frame
push si ;preserve caller's register variables
push di
mov ax,SCREEN_WIDTH
mul [bp+StartY] ;offset in page of top rectangle scan line
mov di,[bp+StartX]
shr di,1
shr di,1 ;X/4 = offset of first rectangle pixel in scan
; line
add di,ax ;offset of first rectangle pixel in page
add di,[bp+PageBase] ;offset of first rectangle pixel in
; display memory
mov ax,SCREEN_SEG
mov es,ax ;point ES:DI to the first rectangle pixel's
; address
mov dx,SC_INDEX ;set the Sequence Controller Index to
mov al,MAP_MASK ; point to the Map Mask register
out dx,al
inc dx ;point DX to the SC Data register
mov cl,byte ptr [bp+StartX]
and cl,011b ;CL = first rectangle pixel's plane
mov al,01h
shl al,cl ;set only the bit for the pixel's plane to 1
mov ah,byte ptr [bp+Color] ;color with which to fill
mov bx,[bp+EndY]
sub bx,[bp+StartY] ;BX = height of rectangle
jle FillDone ;skip if 0 or negative height
mov si,[bp+EndX]
sub si,[bp+StartX] ;CX = width of rectangle
jle FillDone ;skip if 0 or negative width
FillRowsLoop:
push ax ;remember the plane mask for the left edge
push di ;remember the start offset of the scan line
mov cx,si ;set count of pixels in this scan line
FillScanLineLoop:
out dx,al ;set the plane for this pixel
mov es:[di],ah ;draw the pixel
shl al,1 ;adjust the plane mask for the next pixel's
and al,01111b ; bit, modulo 4
jnz AddressSet ;advance address if we turned over from
inc di ; plane 3 to plane 0
mov al,00001b ;set plane mask bit for plane 0
AddressSet:
loop FillScanLineLoop
pop di ;retrieve the start offset of the scan line
add di,SCREEN_WIDTH ;point to the start of the next scan
; line of the rectangle
pop ax ;retrieve the plane mask for the left edge
dec bx ;count down scan lines
jnz FillRowsLoop
FillDone:
pop di ;restore caller's register variables
pop si
pop bp ;restore caller's stack frame
ret
_FillRectangleX endp
end
[LISTING FIVE]
; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
; VGAs. Uses medium-speed approach that selects each plane only once
; per rectangle; this results in a fade-in effect for large
; rectangles. Fills up to but not including the column at EndX and the
; row at EndY. No clipping is performed.
; C near-callable as:
; void FillRectangleX(int StartX, int StartY, int EndX, int EndY,
; unsigned int PageBase, int Color);
SC_INDEX equ 03c4h ;Sequence Controller Index
MAP_MASK equ 02h ;index in SC of Map Mask register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
; to the next
parms struc
dw 2 dup (?) ;pushed BP and return address
StartX dw ? ;X coordinate of upper left corner of rect
StartY dw ? ;Y coordinate of upper left corner of rect
EndX dw ? ;X coordinate of lower right corner of rect
; (the row at EndX is not filled)
EndY dw ? ;Y coordinate of lower right corner of rect
; (the column at EndY is not filled)
PageBase dw ? ;base offset in display memory of page in
; which to fill rectangle
Color dw ? ;color in which to draw pixel
parms ends
StartOffset equ -2 ;local storage for start offset of rectangle
Width equ -4 ;local storage for address width of rectangle
Height equ -6 ;local storage for height of rectangle
PlaneInfo equ -8 ;local storage for plane # and plane mask
STACK_FRAME_SIZE equ 8
.model small
.code
public _FillRectangleX
_FillRectangleX proc near
push bp ;preserve caller'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's register variables
push di
cld
mov ax,SCREEN_WIDTH
mul [bp+StartY] ;offset in page of top rectangle scan line
mov di,[bp+StartX]
shr di,1
shr di,1 ;X/4 = offset of first rectangle pixel in scan
; line
add di,ax ;offset of first rectangle pixel in page
add di,[bp+PageBase] ;offset of first rectangle pixel in
; display memory
mov ax,SCREEN_SEG
mov es,ax ;point ES:DI to the first rectangle pixel's
mov [bp+StartOffset],di ; address
mov dx,SC_INDEX ;set the Sequence Controller Index to
mov al,MAP_MASK ; point to the Map Mask register
out dx,al
mov bx,[bp+EndY]
sub bx,[bp+StartY] ;BX = height of rectangle
jle FillDone ;skip if 0 or negative height
mov [bp+Height],bx
mov dx,[bp+EndX]
mov cx,[bp+StartX]
cmp dx,cx
jle FillDone ;skip if 0 or negative width
dec dx
and cx,not 011b
sub dx,cx
shr dx,1
shr dx,1
inc dx ;# of addresses across rectangle to fill
mov [bp+Width],dx
mov word ptr [bp+PlaneInfo],0001h
;lower byte = plane mask for plane 0,
; upper byte = plane # for plane 0
FillPlanesLoop:
mov ax,word ptr [bp+PlaneInfo]
mov dx,SC_INDEX+1 ;point DX to the SC Data register
out dx,al ;set the plane for this pixel
mov di,[bp+StartOffset] ;point ES:DI to rectangle start
mov dx,[bp+Width]
mov cl,byte ptr [bp+StartX]
and cl,011b ;plane # of first pixel in initial byte
cmp ah,cl ;do we draw this plane in the initial byte?
jae InitAddrSet ;yes
dec dx ;no, so skip the initial byte
jz FillLoopBottom ;skip this plane if no pixels in it
inc di
InitAddrSet:
mov cl,byte ptr [bp+EndX]
dec cl
and cl,011b ;plane # of last pixel in final byte
cmp ah,cl ;do we draw this plane in the final byte?
jbe WidthSet ;yes
dec dx ;no, so skip the final byte
jz FillLoopBottom ;skip this planes if no pixels in it
WidthSet:
mov si,SCREEN_WIDTH
sub si,dx ;distance from end of one scan line to start
; of next
mov bx,[bp+Height] ;# of lines to fill
mov al,byte ptr [bp+Color] ;color with which to fill
FillRowsLoop:
mov cx,dx ;# of bytes across scan line
rep stosb ;fill the scan line in this plane
add di,si ;point to the start of the next scan
; line of the rectangle
dec bx ;count down scan lines
jnz FillRowsLoop
FillLoopBottom:
mov ax,word ptr [bp+PlaneInfo]
shl al,1 ;set the plane bit to the next plane
inc ah ;increment the plane #
mov word ptr [bp+PlaneInfo],ax
cmp ah,4 ;have we done all planes?
jnz FillPlanesLoop ;continue if any more planes
FillDone:
pop di ;restore caller's register variables
pop si
mov sp,bp ;discard storage for local variables
pop bp ;restore caller's stack frame
ret
_FillRectangleX endp
end
[LISTING SIX]
; Mode X (320x240, 256 colors) rectangle fill routine. Works on all
; VGAs. Uses fast approach that fans data out to up to four planes at
; once to draw up to four pixels at once. Fills up to but not
; including the column at EndX and the row at EndY. No clipping is
; performed.
; C near-callable as:
; void FillRectangleX(int StartX, int StartY, int EndX, int EndY,
; unsigned int PageBase, int Color);
SC_INDEX equ 03c4h ;Sequence Controller Index
MAP_MASK equ 02h ;index in SC of Map Mask register
SCREEN_SEG equ 0a000h ;segment of display memory in mode X
SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line
; to the next
parms struc
dw 2 dup (?) ;pushed BP and return address
StartX dw ? ;X coordinate of upper left corner of rect
StartY dw ? ;Y coordinate of upper left corner of rect
EndX dw ? ;X coordinate of lower right corner of rect
; (the row at EndX is not filled)
EndY dw ? ;Y coordinate of lower right corner of rect
; (the column at EndY is not filled)
PageBase dw ? ;base offset in display memory of page in
; which to fill rectangle
Color dw ? ;color in which to draw pixel
parms ends
.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 _FillRectangleX
_FillRectangleX proc near
push bp ;preserve caller's stack frame
mov bp,sp ;point to local stack frame
push si ;preserve caller's register variables
push di
cld
mov ax,SCREEN_WIDTH
mul [bp+StartY] ;offset in page of top rectangle scan line
mov di,[bp+StartX]
shr di,1 ;X/4 = offset of first rectangle pixel in scan
shr di,1 ; line
add di,ax ;offset of first rectangle pixel in page
add di,[bp+PageBase] ;offset of first rectangle pixel in
; display memory
mov ax,SCREEN_SEG ;point ES:DI to the first rectangle
mov es,ax ; pixel's address
mov dx,SC_INDEX ;set the Sequence Controller Index to
mov al,MAP_MASK ; point to the Map Mask register
out dx,al
inc dx ;point DX to the SC Data register
mov si,[bp+StartX]
and si,0003h ;look up left edge plane mask
mov bh,LeftClipPlaneMask[si] ; to clip & put in BH
mov si,[bp+EndX]
and si,0003h ;look up right edge plane
mov bl,RightClipPlaneMask[si] ; mask to clip & put in BL
mov cx,[bp+EndX] ;calculate # of addresses across rect
mov si,[bp+StartX]
cmp cx,si
jle FillDone ;skip if 0 or negative width
dec cx
and si,not 011b
sub cx,si
shr cx,1
shr cx,1 ;# of addresses across rectangle to fill - 1
jnz MasksSet ;there's more than one byte to draw
and bh,bl ;there's only one byte, so combine the left
; and right edge clip masks
MasksSet:
mov si,[bp+EndY]
sub si,[bp+StartY] ;BX = height of rectangle
jle FillDone ;skip if 0 or negative height
mov ah,byte ptr [bp+Color] ;color with which to fill
mov bp,SCREEN_WIDTH ;stack frame isn't needed any more
sub bp,cx ;distance from end of one scan line to start
dec bp ; of next
FillRowsLoop:
push cx ;remember width in addresses - 1
mov al,bh ;put left-edge clip mask in AL
out dx,al ;set the left-edge plane (clip) mask
mov al,ah ;put color in AL
stosb ;draw the left edge
dec cx ;count off left edge byte
js FillLoopBottom ;that's the only byte
jz DoRightEdge ;there are only two bytes
mov al,00fh ;middle addresses are drawn 4 pixels at a pop
out dx,al ;set the middle pixel mask to no clip
mov al,ah ;put color in AL
rep stosb ;draw the middle addresses four pixels apiece
DoRightEdge:
mov al,bl ;put right-edge clip mask in AL
out dx,al ;set the right-edge plane (clip) mask
mov al,ah ;put color in AL
stosb ;draw the right edge
FillLoopBottom:
add di,bp ;point to the start of the next scan line of
; the rectangle
pop cx ;retrieve width in addresses - 1
dec si ;count down scan lines
jnz FillRowsLoop
FillDone:
pop di ;restore caller's register variables
pop si
pop bp ;restore caller's stack frame
ret
_FillRectangleX endp
end
[LISTING SEVEN]
/* Program to demonstrate mode X (320x240, 256-colors) rectangle
fill by drawing adjacent 20x20 rectangles in successive colors from
0 on up across and down the screen */
#include <conio.h>
#include <dos.h>
void Set320x240Mode(void);
void FillRectangleX(int, int, int, int, unsigned int, int);
void main() {
int i,j;
union REGS regset;
Set320x240Mode();
FillRectangleX(0,0,320,240,0,0); /* clear the screen to black */
for (j = 1; j < 220; j += 21) {
for (i = 1; i < 300; i += 21) {
FillRectangleX(i, j, i+20, j+20, 0, ((j/21*15)+i/21) & 0xFF);
}
}
getch();
regset.x.ax = 0x0003; /* switch back to text mode and done */
int86(0x10, ®set, ®set);
}
