> > .....     But what I really want is to plot circles

> You should have said so originally.  Bresenham's circle algorithm:

I invented Bresenham's algorithm 25 years ago to solve a graphics plotting
problem on a VDU. A year ago I found out that the method had a name and that
Bresehnham had beaten me by 17 years ! :-)

For interest, Bresenham is still alive and (apparently) well and replies to
emails. I told him about a local student discovering his work for the first
time in
October last year.
bresenhamj@exchange.winthrop.edu I think I used.

He may appreciate knowing that people are still discovering his brilliant
(albeit retrospectively obvious) concepts decades after the event for
microprocessor use.

It's well worth working out how the algorithm works. Can have application in
other areas.
Note that his original idea used addition only with no multiply/divide at
all - which was very important with the computers of the day - as it is with
PICs :-).

Here's an excellent overview
http://novalis.org/triz-talk-boston-pm/slide-16.html



        RM

_______________

Andy said:

>
>         x = 0
>         y = radius
>         switch = 3 - 2*radius
>
>     loop:
>
>         plot (x,y): plot (x,-y): plot (-x,y): plot (-x,-y)
>         plot (y,x): plot (y,-x): plot (-y,x): plot (-y,-x)
>
>         if switch < 0 then
>             switch = switch + 4 * x + 6
>         else
>             switch = switch + 4 * (x - y) + 10
>             y = y - 1
>
>         x = x + 1
>
>         if x <= y then goto loop
>
>         end
>

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