Rotate 'N' Roll
Dave Millen
Welwyn Garden City,
Hertfordshire.
Rotate 'N' Roll is an intriguing program for any Spectrum
written in Basic, which enables the operator to produce
three-dimensional wire frame images of prisms or poly-
hedrons. The number of sides is optional as is the size of
the drawing. The shapes can be shown as a series of single
frame movements or can be superimposed to create patterns.
Apart from the fascination of the patterns produced, the
program can be a valuable aid to secondary school teachers
of technical graphics to help pupils to visualise objects
in movement.
The rotate facility turns clockwise around a vertical
axis and the roll turns the object clockwise around a
horizontal axis. The size increase gives the impression of
movement towards the viewer. A combination of superimposed
images using all three facilities simulates a solid moving
in space, showing the loci of the sides for specified
movements.
The program can be paused at any stage of drawing by
holding down M. To continue or abort the drawing, follow
the instructions on the screen.
Watching the Demo mode will give the operator an idea of
what can be achieved. In Run mode the operator is required
to program in his/her instructions. Here is a brief expla-
nation of each input in turn. Each input must be terminated
with Enter. Mistakes can be rectified by pressing Caps
Shift and Delete.
Polyhedron - a 3D shape with a flat base, number of sides
optional, and lines from each corner joining in a point.
Example: pyramid.
Prism - a 3D shape with a flat base and top, number of
sides optional. Lines from each corner join the base and
top. Example: cube.
Enter number of sides - This is self-explanatory.
Enter Size (0-140) - Each unit represents one pixel on
the vertical axis at 0 rotation and roll. 140 units is the
maximum size, otherwise the program will stop drawing with
the message "figures too big" when the roll approaches 45.
Enter initial rotation - To establish the starting posi-
tion of the object in degrees. 0 degrees rotation gives a
side view with a flat face towards the viewer. 45 deg.
rotation of a cube would give a corner towards the viewer.
Enter initial roll - Again establishing the starting
position of the object in degrees. 0 degrees roll gives a
side view of the object with the face towards the viewer
determined by the viewer. The top of the object rolls to-
wards the viewer. 90 deg. roll will give a top view of the
object.
Repeat (Y/N) - If the viewer wishes just a drawing of the
object already entered then N should be entered. If a
sequence of drawings is required then enter Y.
How many - Number of drawings required in the sequence.
Enter size inc/dec - To increase or decrease the size of
the object during a sequence. To avoid exceeding the maxi-
mum size the initial size should be subtracted from 140 and
the result divided by the number of repeats previously
entered.
When decreasing in size, enter a minus number in response
to the prompt. If the size reaches 0 before the end of the
sequence it will continue but start increasing in size.
Enter rotation increase - The number of degrees by which
the object must rotate each time, in a sequence. 360 deg.
gives a complete rotation and would give no change. A minus
number causes the object to rotate anticlockwise.
Enter roll increase - The number of degrees by which the
object must roll towards the viewer each time, in a se-
quence. 360 deg. gives a complete roll. A minus number
causes the object to roll away from the viewer.
Superimpose? (Y/N) - If drawings are required as separate
images one after another then enter N. To overlay each
successive drawing onto the previous drawings, in sequence,
enter Y.
Enter paper colour - Use keys 0 to 7 to enter your de-
sired paper colour.
Enter ink colour - Use keys 0 to 7 to enter your desired
ink colour.
The program will now proceed to follow the instructions
entered. Details of each drawing are printed on the left of
the screen display. Rotate 'n' roll is very easy to use and
provides endless fascination for young and old alike.