Thread: Find a "circle" within a matrix

Hi there.

My problem is, that I want to find a "circle" within a matrix, but I just cant wrap my head around it at the moment. It seems like I am having a blockade in my head.
Lets assume we have a big matrix filled with integer numbers, like this:

     0) 1) 2) 3) 4) 5) 6) 7)
0) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
1) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
2) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
3) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
4) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
5) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
6) [ 0, 0, 0, 0, 0, 0, 0, 0 ]

And I specify one of the cells of the matrix and the size of the circle:

matrix.doCircle(column = 3, row = 4, radius = 2.5);

The resulting matrix should look like this:

     0) 1) 2) 3) 4) 5) 6) 7)
0) [ 0, 0, 0, 0, 0, 0, 0, 0 ]
1) [ 0, 0, 0, 1, 1, 1, 0, 0 ]
2) [ 0, 0, 1, 1, 1, 1, 1, 0 ]
3) [ 0, 0, 1, 1, 1, 1, 1, 0 ]
4) [ 0, 0, 1, 1, 1, 1, 1, 0 ]
5) [ 0, 0, 0, 1, 1, 1, 0, 0 ]
6) [ 0, 0, 0, 0, 0, 0, 0, 0 ]

So a circle centered at (3, 4) with the radius 2.5 has been filled with 1's in that matrix.
The circle should be as smooth as possible, and the matrices and radii could get very big.

Does anybody know a good algorithm which would solve this problem in a somewhat effective way?

Thank you very much.