fill optimizations

I have the following recursive implementation of the fill algorithm:

Code:

---

void fill(int x, int y)
{               
        if ( mat[x][y] == 0 )
        {
                mat[x][y] = 1;
                fill(x+1, y);
                fill(x-1, y);
                fill(x, y+1);
                fill(x, y-1);
        }
}

---

I'm wondering, is this efficient? I read that the recursion doesn't slow things down in this case as much as it does in other algorithms, is this true?

Would an interative approach give a significant increase in speed? Is it worth implementing it iteratively, and if so, how would I approach that?

you don't check bounds
you use global variable (are you sure you need it?)
recursion does not slow things down only if it is optimized by compiler...

> I'm wondering, is this efficient?
No. It uses stupid amounts of stack space for even simple shapes.

Do a web search for "scanline fill algorithm".