Path: utzoo!attcan!uunet!actnyc!rmf
From: rmf@actnyc.UUCP (Robert M. Fuhrer)
Newsgroups: comp.graphics
Subject: Re: HP 9000 Screen Dump to HP Laser printer
Summary: HP-UX call to map frame buffer into address space
Message-ID: <919@actnyc.UUCP>
Date: 26 May 88 16:10:40 GMT
References: <286@gt-eedsp.UUCP> <11390009@hpldola.HP.COM>
Reply-To: rmf@actnyc.UUCP (Robert M. Fuhrer)
Organization: InterACT Corporation
Lines: 38

In article <11390009@hpldola.HP.COM> paul@hpldola.HP.COM (Paul Bame) writes:
>> I need a program to do a screen-dump from an HP9000c320.  The images are
>> being done in gray-scale.
>
>graphics(7) in the HP-UX manuals details how to talk directly to the
>frame buffer - it's just a big array - and it's easy to do:
>
>	fd = open(/dev/crt)
>	ioctl(fd, GCMAP?, &ptr)
>
Well, when I was using an HP Series 9000 Model 320 with HP-UX (awhile ago),
I recall finding a system call which maps the frame buffer directly into
the process's address space, so that normal memory references can be made
to the locations representing the pixels.  Of course, anybody can do this,
so it's not generally speaking a good way of *writing* to the screen (since
two processes can interfere with one another), but for reading (e.g., screen
dumping), it's fine.

>>                            The hard-copy devices I have to choose from
>> are an Apple Laserwriter Plus, an HP Laserjet, and a QMS Laserprinter.

Once you've got that, it's very simple to dump bitmaps to a LaserJet (or
LaserJet Plus or II); the following escape sequences exist:

	1) Prepare LJ to receive bitmap data at a given resolution (75, 150,
	   or 300 dpi),
	2) Transfer a raster scan line (telling the LJ how long it is)
	3) End raster transfer mode

I've done both of these procedures (although the LJ part was on an HP320
running their Pascal Development System), and they're both quite easy...

As far as gray scale and/or dithering, I'm not big on that stuff, but it
depends on what sort of image you've got to begin with.
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