Article ID: 51860
Article Last Modified on 11/21/2006
APPLIES TO
- Microsoft QuickBasic 4.0
- Microsoft QuickBASIC 4.0b
- Microsoft QuickBasic 4.5 for MS-DOS
- Microsoft BASIC Compiler 6.0
- Microsoft BASIC Compiler 6.0b
- Microsoft BASIC Professional Development System 7.0
- Microsoft BASIC Professional Development System 7.1
This article was previously published under Q51860
SUMMARY
The program listing below demonstrates one method of printing VGA SCREEN 13 images to an Epson (or compatible) printer with graphics capability.
This information applies to Microsoft QuickBasic versions 4.00, 4.00b, and 4.50 for MS-DOS, to Microsoft Basic Compiler versions 6.00 and 6.00b for MS-DOS, and to Microsoft Basic PDS (Professional Development System) versions 7.00 and 7.10 for MS-DOS. (Earlier versions do not support VGA SCREEN 13.)
MORE INFORMATION
If you have a printer other than an Epson-compatible, you must change the printer control codes used in the following program for setting line spacing and graphics mode. Control codes can be found in your printer's manual.
The routine below for printing VGA SCREEN mode 13 is required only if you aren't running under MS-DOS versions 4.00 or later. In MS-DOS 4.00 and later, the program GRAPHICS.COM supports all standard EGA and VGA SCREEN modes. Thus, the routine given in a separate article (part of this application note) for printing CGA SCREEN modes can be used to print EGA and VGA SCREENs in MS-DOS 4.00 and later.
Printing VGA Screen Mode 13
The method used in the program below prints the image sideways, which avoids the need to do any bit-shifting and uses a simple eight-dots-per-pixel shading pattern to represent different colors.
To produce different patterns for different colors, each byte of pixel information must be analyzed. In SCREEN 13, each pixel is represented by 1 contiguous byte of information, thus allowing 256 colors per pixel. Since 8 printer pins are fired for each pixel, a direct mapping of the pixel byte to the printer pins to be fired is done.
As stated before, 8 pins are fired for each pixel; the pins are fired in a 2 by 4 pattern. Since this is not square, some slight image distortion does occur.
The Epson printer can fire up to eight pins per graphics byte sent. Thus, moving from left to right, a loop that reads screen data from the bottom of the screen upward can access eight vertical columns at a time. This behavior coincides with the printer firing eight pins at a time and creates eight horizontal columns on the page, turning the printout sideways.
DECLARE SUB VGAtoEpson (f$, flip%)
'--- VGAEPSON.BAS
'--- Demonstrates the use of VGAtoEpson, a subprogram that
'--- dumps a SCREEN 13 image to an Epson printer.
'--- Copyright (c) 1988 Microsoft Corp.
REM $INCLUDE: 'QB.BI'
DIM SHARED inregs AS regtype
DIM SHARED outregs AS regtype
SCREEN 13
'--- Draw picture on screen
xmax% = 319
ymax% = 199
halfx% = xmax% / 2
halfy% = ymax% / 2
x% = halfx%
c% = 1
FOR y% = ymax% TO halfy% STEP -2
LINE (halfx%, y%)-(x%, halfy%), c%
LINE (x%, ymax%)-(xmax%, y%), c% + 20
LINE (halfx%, (ymax% - y%))-(x%, halfy%), c% + 40
LINE (x%, 0)-(xmax%, (ymax% - y%)), c% + 60
LINE (halfx% + 1, y%)-((xmax% - x%), halfy%), c% + 80
LINE ((xmax% - x%), ymax%)-(0, y%), c% + 100
LINE (halfx%, (ymax% - y%))-((xmax% - x%), halfy% + 1), c% + 120
LINE ((xmax% - x%), 0)-(0, (ymax% - y%)), c% + 140
x% = x% + (((xmax% + 1) / (ymax% + 1)) * 5)
c% = c% + 1
NEXT y%
CALL VGAtoEpson("LPT1", 1)
SCREEN 0
END
SUB VGAtoEpson (f$, flip%) STATIC
'--- Sends the image on SCREEN 13 to an Epson graphics printer
'--- Parameters:
' f$ - Name of file or device to send image to
' flip% - Invert flag (0 = normal, not 0 = invert)
OPEN f$ FOR BINARY AS 1 'Open the output file
WIDTH #1, 255
esc$ = CHR$(27)
line$ = esc$ + "A" + CHR$(8)
PUT #1, , line$ 'set printer to 8/72 lpi
DEF SEG = &HA000 'Start of VGA screen memory
'--- This loop is the horizontal byte location
FOR Col% = 0 TO 79
'--- Set the printer to receive 800 bytes of graphics data
line$ = esc$ + "L" + MKI$(800)
PUT #1, , line$ '(for init)
'--- This loop is the vertical byte position
FOR row% = 199 TO 0 STEP -1
place& = row% * 320&
place& = place& + Col% * 4
' 4 bytes of pixel information are read in. Each
' of these bytes is broken up across 4 variables
' that are used to fire the printer pins. 2 bits
' from each pixel byte are stored to each of the
' variables.
mem1% = 0 ' Initialize storage bytes for
mem2% = 0 ' color information.
mem3% = 0
mem4% = 0
FOR byte% = 0 TO 3
newplace& = place& + byte%
shift% = 2 ^ ((7 - 2 * byte%) - 1)
mem% = PEEK(newplace&)
mem% = mem% AND 3
mem% = mem% * shift%
mem1% = mem1% OR mem%
mem% = PEEK(newplace&)
mem% = (mem% AND 12) / 4
mem% = mem% * shift%
mem2% = mem2% OR mem%
mem% = PEEK(newplace&)
mem% = (mem% AND 48) / 16
mem% = mem% * shift%
mem3% = mem3% OR mem%
mem% = PEEK(newplace&)
mem% = (mem% AND 192) / 64
mem% = mem% * shift%
mem4% = mem4% OR mem%
NEXT
'--- Flip the byte, if called from
IF flip% <> 0 THEN
mem1% = 255 - mem1%
mem2% = 255 - mem2%
mem3% = 255 - mem3%
mem4% = 255 - mem4%
END IF
'--- Send bytes to device
line$ = CHR$(mem1%) + CHR$(mem2%)
line$ = line$ + CHR$(mem3%) + CHR$(mem4%)
PUT #1, , line$
NEXT
line$ = CHR$(13) + CHR$(10)
PUT #1, , line$
NEXT
ResetPrn$ = esc$ + "@"
PUT #1, , ResetPrn$ ' Reset printer
line$ = CHR$(12)
PUT #1, , line$ ' Send formfeed (page eject)
CLOSE 1 ' All done
END SUB
REFERENCES
This article is part of a collection of articles explaining how to print Basic video screens to Epson printers. Find the entire collection by querying in the Microsoft Knowledge Base using the following words:
Epson and print and screen and QuickBasic
If you want further information about graphics memory and the various graphics modes, please refer to the following book, which is available in bookstores or by calling Microsoft Press at (800) 888-3303 or (425) 882-8661:
"Programmer's Guide to PC and PS/2 Video Systems," by Richard Wilton (published by Microsoft Press, 1987)
Additional query words: QuickBas
Keywords: KB51860
