Power-Programmierung/CD2.mdf/tools/pcap/pcap.txt

Text File | 1991-02-28 | 6KB | 120 lines

Documentation for PCAP - A Screen Capture Utility.
2/28/91

What it does ...

PCAP saves the image on your computer monitor to a hard disk file. The file is
actually a DOS program (in COM format instead of EXE). When you run the
program, the image will be displayed on your screen. PCAP is a memory resident
program so it will steal some of your computers RAM but not much (only about
4K). It will save text screens as well as CGA, EGA, MCGA and VGA graphics.

Why you might want to use it ...

About the only thing I do with it is save PRODIGY screens like the weather
maps. Actually, I have my PC setup to dial in to PRODIGY everyday and grab the
weather maps automatically so that they are waiting for me when I get to work
(OK, so I'm a nerd). I also use PAN, a program automation (animation?) utility
from PC-Mag, to do this. I'm including the PAN script file (minus my PASSWORD)
that I use in case you want to try this. You'll have to get PAN somewhere
else, though.

Loading PCAP ...

Just run PCAP. The first time you do, it'll try to create a directory on drive
C:, namely "C:\PCAPT". This is the directory where all the images will be
saved.

Saving an image ...

Press ALT-P when you want to save the image on the screen. PCAP will sound 1
long beep followed by a series of short beeps followed by another long beep.
The last beep means that the image is saved. The length of time it takes to
save the image will depend on if it is text (very fast), low (fast) or high
(slower) resoultion graphics and on the speed of your computer.

* You should not try to do anything else but wait while the screen is saving *

Displaying an image ...

All the images will be stored in files in the C:\PCAPT directory. They will
have names *like* 0C13445D and no extensions. These names are given by DOS as
the result of a "create unique file" call. Before you can display an image,
you must rename the file to <name>.COM where '<name>' stands for anything you
want. You might want to make it descriptive like MAP.COM or NEWS.COM. If you
just want to put the 'COM' extension on all the image files in the directory,
you can use the DOS RENAME command like this:

                           REN C:\PCAPT\*. *.COM

After you've but a COM extension (and optionally changed the file name) simply
type in the file name at the DOS prompt to see the image. It will remain on
the screen until any key is pressed.

Things you should know ...

I wrote this program a long time ago before I did any multitasking on my PC.
Consequently, I didn't pay much attention to trying to safeguard against
problems that can happen when TSR's and multitasking combine. About the only
thing I did do was to set a flag so that you can't accidently press the ALT-P
key combo too long and call the PCAP code again before it's done. This would
certainly screw up something. I use PCAP with Windows now and everything works
fine although I am careful to let it finish saving the screen before I do
anything. The only strange thing I've run across is that after saving a
Prodigy screen, the blinking box that acts as a cursor does not blink anymore
and the mouse won't work until a key is pressed. After any key is pressed
everything returns to normal.

PCAP won't work with the Hercules graphics modes or the 256 color MCGA nad VGA
modes. I never had time to do these. PCAP will work with most text modes and
all the CGA, EGA, MCGA and VGA graphics modes (with the exception of the 256
color modes). Once an image file is created, the graphics and text mode is
saved along with the image. The image can only be displayed on a system that
is capable of using the saved graphics or text mode. For instance, if you save
a VGA mode graphics image on one PC and try to display it on another PC with a
CGA card, you'll see a blank screen. The converse will work, however, because
the VGA supports all the standard graphics and text modes of the CGA.

If you use PCAP with an EGA, sometimes the colors that the image file displays
will be different that those at the time of capture. This is because the EGA
has write only registers and there is no foolproof way of saving the palette.
I have included a file called PRODEGA.DBG that will help you get the right
colors for PROGIGY when using an EGA. It is the input to the DOS DEBUG program
that pokes the right values for the palette registers into the image file. To
use it you'll need DEBUG. For an example, say your image file is a PRODIGY
weather map and has been renamed to "MAP.COM" and the colors are way off when
you display it because you have an EGA. If you have DEBUG, run it against
"MAP.COM" and redirect the input to "PRODEGA.DBG". The command looks like:

                      DEBUG MAP.COM < PRODEGA.DBG

Try running MAP.COM again.

Format of image files ...

The image file consists of the saved mode information, the code to display the
image and the image data itself. The image data is run-length coded. I'll send
the format to anybody who asks (see the end of this file for my e-mail
address). It's very simple to decompact. It works very well on PRODIGY
screens, even in the high resolution (640x480x16) mode. I get about 3.75:1
compaction on the maps and these are about the most complex screens in
PRODIGY. However, there is the potential that an image file will be greater
than 64K, especially in the high res VGA mode. If this happens then the image
file won't display because COM files are limited to a 64K image on disk. I've
never had this happen with PRODIGY screens but it does happen on some very
complex images from other programs.

The end ...

I know this is a very sparse program. There are many, many, features that can
be added to enhance it. If you have any suggestions, comment or ideas, you can
sent them to me on Prodigy or Internet.

- Tom Cervenka, Prodigy: CMGB18A, Internet: [e-mail]