Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!brutus.cs.uiuc.edu!ux1.cso.uiuc.edu!tank!cps3xx!flynn
From: flynn@pixel.cps.msu.edu (Patrick J. Flynn)
Newsgroups: comp.sys.next
Subject: Direct access to screen pixels
Message-ID: <5963@cps3xx.UUCP>
Date: 9 Jan 90 19:32:05 GMT
Sender: usenet@cps3xx.UUCP
Reply-To: flynn@pixel.cps.msu.edu (Patrick J. Flynn)
Organization: Pixels from Hell
Lines: 47

WARNING: fooling around with the system can cause serious problems.

Now that the faint-hearted are scared away...

Here's some code which allows one to abuse the screen pixels directly.
As written, it saves the screen in a buffer, fills it with random
texture, and then restores the contents of the screen from the buffer.
See <nextdev/video.h> for the ioctl codes and cAPitAliZeD constants.
Note that the NeXT screen is advertised as 1120x832, but seems to be
laid out in memory as 1152x910. Hmm, I wonder where the 1152 came
from...  :-).

Disclaimer: this was a ten-minute hack.  Any or all of the info in
the preceding paragraph could be wrong. Don't blame me if your
cube's magnesium case catches on fire when you try this.
Also, don't laugh too hard at my C coding style.

--------------------------------------------------
#include <sys/file.h>
#include <sys/ioctl.h>
#include <nextdev/video.h>

#define NPIX VIDEO_MW*VIDEO_H

main()
 {
   char *addr; /* base addr of video RAM */
   char buf[NPIX/4];
   int fd,i;
   fd=open("/dev/vid0",O_RDWR,0);
   /* get video ram base addr. */
   if (ioctl(fd, DKIOCGADDR, &addr) == -1) perror("ioctl:DKIOCGADDR");
   /* save the screen */
   bcopy(addr,buf,NPIX/4);
   /* stomp all over the screen */
   for(i=0;i<NPIX/4;i++) addr[i]=random();
   /* let the user see what he hath wrought */
   sleep(1);
   /* restore the screen */
   bcopy(buf,addr,NPIX/4);
   close(fd);
 }
--------------------------------------------------

See ya -- Pat
--
Patrick Flynn, CS, Mich. State U., flynn@cps.msu.edu