Pie Chart Algorithms?

Alex Tweedly alex at tweedly.net
Wed Mar 1 17:32:24 EST 2006


Sivakatirswami wrote:

> Now my next challenge is to get a list of points on the circumference  
> of any circle.  I checked the mailing lists and can't find the  
> algorithm or sample script that would do this. If anyone has the  
> "professional" algorithm to do this please do post it... /H's chart  
> stack is protected...
>
Not professional, but maybe "interested amateur" :-)
(this returns floating point numbers - remember to convert to integers 
before using as points of a polygon or similar)

on mouseUp
  put getPoints(100,100,10) after msg
end mouseUp
 
function getPoints xc, yc, rad
  --  returns a list of points on the circumference of a circle
  -- centered at xc,yc with radius rad
 
  repeat with i = 0 to 90
    put  xc+ rad*sinInDegrees(i), yc+rad*cosInDegrees(i) & CR after tResult
  end repeat
  return tResult
end getPoints


function cosInDegrees angleInDegrees
  return cos(angleInDegrees * pi / 180)
end cosInDegrees


function sinInDegrees angleInDegrees
  return sin(angleInDegrees * pi / 180)
end sinInDegrees


>
> And a related issue: move grc "ball" to the points of grc "oval"  
> doesn't do anything... oval's don't have any points (?) doesn't make  
> sense to me: any line object on a screen is a series of pixels... how  
> can it not have points?
>
Polygons are defined by a set of points
Ovals are defined by a centre and radius (or radii)

When either of them is drawn, some pixels are coloured in; in the case 
of a polygon, far more pixels will be coloured in than are in "the 
points" of the poly.



-- 
Alex Tweedly       http://www.tweedly.net



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