Circle line-segment collision detection algorithm?

Question

I have a line from A to B and a circle positioned at C with the radius R.

What is a good alg

Answer 1

Just an addition to this thread... Below is a version of the code posted by pahlevan, but for C#/XNA and tidied up a little:

    /// 

    /// Intersects a line and a circle.
    /// 
    /// the location of the circle
    /// the radius of the circle
    /// the starting point of the line
    /// the ending point of the line
    /// true if the line and circle intersect each other
    public static bool IntersectLineCircle(Vector2 location, float radius, Vector2 lineFrom, Vector2 lineTo)
    {
        float ab2, acab, h2;
        Vector2 ac = location - lineFrom;
        Vector2 ab = lineTo - lineFrom;
        Vector2.Dot(ref ab, ref ab, out ab2);
        Vector2.Dot(ref ac, ref ab, out acab);
        float t = acab / ab2;

        if (t < 0)
            t = 0;
        else if (t > 1)
            t = 1;

        Vector2 h = ((ab * t) + lineFrom) - location;
        Vector2.Dot(ref h, ref h, out h2);

        return (h2 <= (radius * radius));
    }