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Circle to 2D-array

Started by Doggolainen Dec 19, 2011 at 9:03 PM 1 replies 2.1k views

Original Post

Dec 19, 2011 at 9:03 PM

I want to remove the overlap between a 2D-array containing a circle and another 2D-array containing alpha values of a pictures. (Think an explosion in liero or worms)

But my problem is creating the circle 2D-array from a given radius. I've been looking into the midpoint circle algorithm a little bit, but I cant find any good hits on filled circles.

int[,] CreateCircle(float radius)
{
//return a int matrix where 1 is a pixel part of the circle and 0 is outside the circle
}

luca-deltodesco

Dec 20, 2011 at 12:46 AM

Why can you not use the midpoint circle algorithm?

http://en.wikipedia....ircle_algorithm

taking the first source example, you get in each iteration:


 setPixel(x0 + x, y0 + y);
 setPixel(x0 - x, y0 + y);
 setPixel(x0 + x, y0 - y);
 setPixel(x0 - x, y0 - y);
 setPixel(x0 + y, y0 + x);
 setPixel(x0 - y, y0 + x);
 setPixel(x0 + y, y0 - x);
 setPixel(x0 - y, y0 - x);

just replace with:

 
 for(ix = x0-x; ix<=x0+x; ix++) {
 setPixel(ix, y0 + y);
 setPixel(ix, y0 - y);
 }
 for(ix = x0-y; ix<=x0+y; ix++) {
 setPixel(ix, y0 + x);
 setPixel(ix, y0 - x);
 }

and you can do the same with the improved version

LorenzoGatti

Dec 20, 2011 at 9:17 AM

Shouldn't you use a sprite (possibly the alpha channel of the explosion image: opaque=destroyed, transparent=untouched, partly transparent=use a threshold to decide) instead of calculating circles over and over again at runtime? Sprites allow you to use any explosion shape, not only discs, and build complex explosions by compositing multiple particles.

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