Page 15 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Unit 1: Fundamentals of Computer Graphics

The exact quantification of the value of imagery versus text appears to vary somewhat with Notes
subject matter, and is probably better left to psychologists and social scientists. But there is little
question of the kernel of truth in the saying, and it has been a driver of computer architecture
for many years.

Computer graphics are taken for granted today. But it has been a long and painful struggle, with
hardware rarely keeping up with the demand for better images. In English, there are a relatively
small number of characters which comprise text. The same is not true of images: graphics are
computationally intensive. They always seem to take as much speed and memory as there are
available. But the demand was high enough that early computer graphics could be fairly crude
and still be in demand.
The advance in computer graphics was to come from one MIT student, Ivan Sutherland. In 1961
Sutherland created another computer drawing program called Sketchpad. Using a light pen,
Sketchpad allowed one to draw simple shapes on the computer screen, save them and even
recall them later. The light pen itself had a small photoelectric cell in its tip. This cell emitted an
electronic pulse whenever it was placed in front of a computer screen and the screen’s electron
gun fired directly at it. By simply timing the electronic pulse with the current location of the
electron gun, it was easy to pinpoint exactly where the pen was on the screen at any given
moment. Once that was determined, the computer could then draw a cursor at that location.
Sutherland seemed to find the perfect solution for many of the graphics troubles he faced. Even
today, many standards of computer graphics interfaces got their start with this early Sketchpad
program. One example of this is in drawing constraints. If one wants to draw a square for example,
it does not have to worry about drawing four lines perfectly to form the edges of the box. One
can simply specify that she/he wants to draw a box, and then specify the location and size of the
box. The software will then construct a perfect box, with the right dimensions and at the right
location. Another example is that Sutherland’s software modelled objects - not just a picture of
objects. In other words, with a model of a car, one could change the size of the tires without
affecting the rest of the car. It could stretch the body of the car without deforming the tires.

These early computer graphics were Vector graphics, composed of thin lines whereas modern
day graphics are Raster based using pixels. The difference between vector graphics and raster
graphics can be illustrated with a shipwrecked sailor. He creates an SOS sign in the sand by
arranging rocks in the shape of the letters “SOS.” He also has some brightly coloured rope,
with which he makes a second “SOS” sign by arranging the rope in the shapes of the letters.
The rock SOS sign is similar to raster graphics. Every pixel has to be individually accounted
for. The rope SOS sign is equivalent to vector graphics. The computer simply sets the starting
point and ending point for the line and perhaps bends it a little between the two end points.
The disadvantages to vector files are that they cannot represent continuous tone images and
they are limited in the number of colours available. Raster formats on the other hand work well
for continuous tone images and can reproduce as many colours as needed.
Also in 1961 another student at MIT, Steve Russell, created the first video game, Spacewar.
Written for the DEC PDP-1, Spacewar was an instant success and copies started flowing to
other PDP-1 owners and eventually even DEC got a copy. The engineers at DEC used it as a
diagnostic program on every new PDP-1 before shipping it. The sales force picked up on this
quickly enough and when installing new units, would run the world’s first video game for
their new customers.

E. E. Zajac, a scientist at Bell Telephone Laboratory (BTL), created a film called “Simulation of a
two-giro gravity attitude control system” in 1963. In this computer produced film, Zajac showed
how the attitude of a satellite could be altered as it orbits the Earth. He created the animation
on an IBM 7090 mainframe computer. Also at BTL, Ken Knowlton, Frank Sindon and Michael
Noll started working in the computer graphics field. Sindon created a film called Force, Mass
and Motion illustrating Newton’s laws of motion in operation. Around the same time, other

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