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[RAY CATZEL <learn@computerpals.on.ca>]

We use microworlds with great success with kids aged 6 upwards. I have avoided 
more complicated routines because it would be beyond most of my students. 
However I have one student (12 years old) who is way ahead of others and is 
very keen on programming in 3D virtual reality - similar to some of the violent 
games such as Descent, etc.
Through his own research he has discovered that programming techniques such as 
array manipulation, rotation and 3D plotting are involved.

We are working in Microworlds Windows95 Logo. He has produced the following 
routines:

ARRAY HANDLING ROUTINE

to array_index :array :index
local "bdist
make "a_index :array
make "bdist (count :array) - :index - 1
repeat :index [make "a_index butfirst :a_index]
repeat :bdist [make "a_index butlast :a_index]
end

3D PLOTTING ROUTINE

to draw :x :y :z
setpos list (:x * 256) / :z (:y * -256) / :z
end

to cube
ht
cg
line -10 10 20 -10 10 40
line -10 10 20 -10 -10 20

line 10 10 20 -10 10 20
line 10 10 20 10 10 40
line 10 10 20 10 -10 20

line 10 -10 20 10 10 20
line 10 -10 20 -10 -10 20
line 10 -10 20 10 -10 40

line -10 -10 20 10 -10 20
line -10 -10 20 -10 10 20
line -10 -10 20 -10 -10 40

line -10 -10 40 10 -10 40
line -10 -10 40 -10 10 40
line -10 -10 40 -10 -10 20

line -10 10 40 -10 -10 40
line -10 10 40 10 10 40
line -10 10 40 -10 10 20

line 10 -10 40 -10 -10 40
line 10 -10 40 10 10 40
line 10 -10 40 10 -10 20

line 10 10 40 10 -10 40
line 10 10 40 -10 10 40
line 10 10 40 10 10 20
end

to line :x :y :z :x2 :y2 :z2
pu
draw :x :y :z
pd
draw :x2 :y2 :z2
pu
end

ROTATION ROUTINE

to rot
cg
pu
setpos [1 200]
pd

forever [
make "x xcor
make "y ycor
setx  ((sin 89.9) * :x)  - ((cos 89.9) * :y)
sety  ((cos 89.9) * :x)  + ((sin 89.9) * :y)
]

end

I am sure that he has picked up some of these techniques from other programming 
languages. Could you please comment on these programming techniques and how 
they might be better coded in Logo.

Thank you.

Ray Catzel
President  ComputerPals
Email:  learn@computerpals.on.ca
Internet:  http://www.computerpals.on.ca/~pals

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