円と線分の交差判定

Unityで使える円と線分の交差判定です。

コード

IsLineIntersectedCircle.cs

/// <summary>
/// 円と線分の交差判定
/// </summary>
private bool IsLineIntersectedCircle( Vector2 a, Vector2 b, Vector2 p, float radius )
{
    Vector2 ap = p - a;
    Vector2 ab = b - a;
    Vector2 bp = p - b;
    Vector2 normalAB = ab.normalized;

    float lenAX = Vector2.Dot( normalAB, ap );

    float shortestDistance = 0.0f;
    if ( lenAX < 0 )
    {
        shortestDistance = ap.magnitude;
    }
    else if( lenAX > ab.magnitude )
    {
        shortestDistance = bp.magnitude;
    }
    else
    {
        shortestDistance = Mathf.Abs(Vector3.Cross(normalAB, ap).magnitude);
    }

    Vector2 X = a + ab * lenAX;
    return shortestDistance < radius;
}

参考