While coding on a Palm OS game yesterday, I created a simple circle drawing algorithm based on sine and cosine of an angle. The circles it drew were of very low quality – and I set out to find a better circle drawing algorithm.
After a few hours of searching, I finally found this page:
http://www.cs.unc.edu/~mcmillan/comp136/Lecture7/circle.html
It explains a rather simple algorithm that works very well – should you ever need a custom circle drawing routine(no, the Palm OS’s doesn’t do it here), you will be very happy to have this page at hand!
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The demo code only seems to support diameters in odd number of pixels.
I haven’t taken the time to analyze the approach for validity with even count diameters.
Obviously it could be adapted, if this is indeed a shortcoming.
Actually, if you only need a circle, you can use WinDrawRectangle, like so
RectangleType r = { 10, 10, 100, 100 };
WinDrawRectangle(&r, 50);
The second parameter is the radius of the circle placed at each corner. This would draw a circle that’s centered at 60,60 of radius 50.
This isn’t useful for ellipses, but for circles it works nicely.
Hi Ben,
I did that – but it isn’t enough for me any more=).
You will see why I need the new algorithm very soon – in fact, send me an email and I will show you now!
Best regards
Tam Hanna
@ReadOnly
The odd sized diameter is more a result of the definition of the circle (center with a radius that are both integers) than the algorithm itself. But the main point is that these algorithms were made back when computation resources were at a premium and being able to draw a good looking circle with just integer operations was a necessity.
Also, the link from the article appears to be dead, so here’s a related article on wikipedia:
http://en.wikipedia.org/wiki/Midpoint_circle_algorithm