Description: Movie-making article for Newsletter                  
From: ANDREWS      Date: 30-NOV-1987

\magnification=\magstep1
\baselineskip=15pt\parskip=5pt plus 2 pt
\centerline{\bf How to Make Movies at PSC \rm or, \it Animation for the Masses}
\bigskip
One advantage of designing any graphics systems from
scratch is the possibility of creating a uniform interface to various
output devices. At PSC we have standardised on the
CGM format for the interchange of two-dimensional graphics data,
a choice that is rapidly becoming prevalent in the supercomputing
world.
 
One aim of this approach is to facilitate the routine production of
computer animated movies by our users. Plainly speaking, any PSC user
should be able to view his graphical output in a movie format
by creating a CGM file, containing a series of frames, and having
it output at PSC on video tape.
The resultant tape, in either UMATIC or VHS format,
is then mailed to the user.
This process has already been performed on an experimental basis and we
would like to encourage more users to participate as we build up our
experience in this area.
 
The technical details are simple; GPLOT (our CGM file processor) knows
about two different kinds of devices: output devices and controllers.
When you use the command GPLOT/DEVICE=PS you are telling GPLOT to
produce output for a PostScript printer. If you use GPLOT/SCREEN=4010
you are telling GPLOT three things, to produce output for a Tektronix
4010 compatible terminal, to send that output directly to the user's
terminal, and to ``beep'' the user's terminal at the end of each frame
and wait for a response before drawing the next frame. The {\it output
device} was a Tektronix 4010 and the {\it controlling device} was the
user's terminal.
 
Moviemaking works in a similar manner, as the following diagram shows.
 
% all the special stuf to make th diagram work
\newdimen\boxht\newdimen\boxwd
\def\myspot#1#2#3{\special{cgm 1 #1 #2 #3}}
\def\vrulefill{\leaders\vrule\vfill }
\def\mybox#1#2#3#4#5{\setbox0=#1\boxht = \ht0\boxwd = \wd0
\advance\boxht by 10pt\advance\boxwd by 10pt
\vbox{\hsize=\boxwd
	\line{\hrulefill #2\hrulefill}\nointerlineskip
	\line{\vbox to \boxht{\vrulefill #5\vrulefill}\hfil
	    \vbox to \boxht{\vfil\box0\vfil}\hfil
	    \vbox to \boxht{\vrulefill #3\vrulefill}}\nointerlineskip
	\line{\hrulefill #4\hrulefill
}}}
% now the actual diagram
\vfil\penalty-100\vfilneg	% optional break
\centerline{{\vbox to 4 true in {\hsize=4truein
\font\big=cmr10 scaled \magstep1\big	% make the text a little bigger
\setbox1=\hbox{FILE}
\centerline{\mybox{\vbox{\hsize=\wd1\centerline{CGM}\box1}}\relax\relax
{\myspot1 2 1}\relax}
\vfill
\centerline{\mybox{\hbox{GPLOT}}{\myspot1 2 2}{\myspot2 2 1}\relax
{\myspot3 2 1}}
\vfill\vfill
\line{\mybox{\hbox{PERITEK}}{\myspot3 2 2}\relax{\myspot4 2 1}\relax\hfil
	\mybox{\hbox{DIAQUEST}}{\myspot2 2 2}\relax{\myspot5 2 1}\relax}
\vfill\vfill
\setbox1=\hbox{SONY}
\centerline{\mybox
	{\vbox{\hsize=\wd1\box1\centerline{VTR}}}\relax
	{\myspot5 2 2}{\myspot6 2 1}{\myspot4 2 2}\relax
}
\vfill\vfill
\setbox1=\hbox{UMATIC}
\centerline{\mybox
	{\vbox{\hsize=\wd1\box1\centerline{TAPE}}}{\myspot
	6 2 2}\relax{\myspot7 2 1}\relax
}
\vfill
\setbox1=\hbox{TAPE}
\centerline{\mybox
	{\vbox{\hsize=\wd1\centerline{VHS}\box1}}{\myspot
	7 2 2}\relax\relax\relax
}
\vfill
}}}
%end of diagram
 
\bigskip
The PERITEK is a colour frame buffer, with a resolution of 512x512 pixels,
the value of each pixel acting as an index into a colour map.
Our PERITEK is hosted by a
MicroVAX at PSC.
The output of the PERITEK is an RGB feed (separate red, green and blue
signals) which can be massaged
by an external encoder into an NTSC signal
suitable for videotape. NTSC is the encoding format
used by the television industry.
 
The PERITEK is the {\it output device} for GPLOT in this procedure,
however with this configuration we cannot draw the frames quickly enough
to send the video directly to a recorder. Instead of a new frame from the CGM
file appearing on each frame of the videotape, you would actually see the
individual frames being drawn, and the animation effect would be lost.
This is because, with a microvax/peritek combination, we cannot process the
CGM file and update the screen in the 1/30 of a second the videotape allots
for each frame. Typically times of the order of a second are required for such
an update.
 
To synchronise our frame production and the recording process of the VTR
(video tape recorder) we use a SONY UMATIC recorder together with a
DIAQUEST controller.
The DIAQUEST is the {\it controlling device} for GPLOT in this case,
capable of positioning the VTR at any individual frame
position and causing one or more frames to be recorded there. Thus GPLOT
will run through the user's CGM file, drawing each frame on the PERITEK
frame buffer and causing the DIAQUEST controller to lay down
consecutive frames of the CGM file on the UMATIC tape in the SONY VTR.
As you might expect the command sequence for GPLOT is
GPLOT/DEV=PERITEK/CTR=DIAQUEST filename.
 
Because of the increased overhead in locating the correct frame on the
videotape (the recorder must backup and pre-roll to arrive at the
correct frame with the tape moving past the heads at the requisite speed)
each frame takes roughly 10 seconds to process.
When the file is exhausted, the movie can be dubbed to VHS (for those of
you who don't have UMATIC tape players) and the tape mailed to the
user. Remember that the default video speed is 30 frames/second and use
that as your guide to how many frames you should produce. However we can
``pad'' the image by laying down consecutive duplicate frames,
though this may lead to jerkiness in the finished animation.
 
We are presently using a dedicated microvax at PSC for this procedure,
so one our staff will have to create the tape for you. For more
information on how you should go about getting your movie produced
send mail on the front ends to WELLING.
 
\bigskip\noindent
--Phil Andrews
 
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