Popular Computing Weekly 02/12/1982 Page 7

Letters

Angling into correct formulae

In your issue date October 28, Andrew Esmond's formulae are incorrect. They
only work for a rotation of 45 deg. as SIN 45 = COS 45. Any other angle put
through his formula gives some very obscure graphics. The correct formulae are:

X=X COS 0-Y SIN 0
Y-Y COS 0+X SIN 0

Here is a program for the Spectrum which allows a cube to be rotated in three
directions using INKEY$:

0 - Around
7 = UP
8 - Right

I have also improved the perspective so that there is a continuous decreasing
in scale for any value of z. Variable RO is the angle through which the cube is
rotated and s is its size. Deleting line 1010 can give some very interesting
graphics.

A Howes
23 The Hazels
Wigmore
Gillingham
Kent
ME8 0SE.



Popular Computing Weekly 30/12/1982 Page 15

Open Forum

Parachutist On Spectrum
By Andrew Astrand

The first thing to do on running this program is to load the user-defined
characters. Type in and RUN lines 10-30 first. User-defined characters are used
in lines:

90 	'B+8+C' - 'A'
100 	'D+E'
101 	'F+G'
102 	'A'
120 	'SPC+H+I+I+J+SPC'
140 	'L'
170 	'K' - 'L'

Use the Keys "j" to jump out of the plane, and "p" to pull ripcord to release
your parachute. The object of the game is to land on the little island to score
points, the flag will point in the direction of the wind. So when you pull the
ripcord, you will then travel in that direction of the wind. You only have 10
attempts to jump out of the plane before the game ends, and your score is
displayed on screen, before been asked for another go. If you don't pull your
ripcord you will fall to your death and the game will suddenly end.

Instructions are included in the game.

Note: Line 9 GOTO 40 was removed from the original listing, because this line
skipped the READ DATA statements in lines 10 to 30. So when RUN with line 9
included, the user defined graphics won't be displayed.
