gistfile1.cs

foreach (var wall in walls)
{
    /*
        ╔═T═╗
        L   R
        ╚═B═╝
    */
    var bounds = wall.Bounds;
    var point = Vector2.Zero;

    var top = bounds.Top;
    var bottom = bounds.Bottom;
    var left = bounds.Left;
    var right = bounds.Right;
    var x = current.Position.X;
    var y = current.Position.Y;


    #region Corners
    if (x < left && y < top)
    {
        point = new Vector2(left, top);
        if (current.HasOverlap(point))
        {
            hasAnyOverlap = true;

            var dx = current.Position.X - point.X;
            var dy = current.Position.Y - point.Y;
            var sr = current.Radius;
            var d = Math.Sqrt(dx * dx + dy * dy);
            current.Position.X = (Single)(point.X + (dx / d) * sr);
            current.Position.Y = (Single)(point.Y + (dy / d) * sr);
        }
    }

    if (x > right && y < top)
    {
        point = new Vector2(right, top);
        if (current.HasOverlap(point))
        {
            hasAnyOverlap = true;

            var dx = current.Position.X - point.X;
            var dy = current.Position.Y - point.Y;
            var sr = current.Radius;
            var d = Math.Sqrt(dx * dx + dy * dy);
            current.Position.X = (Single)(point.X + (dx / d) * sr);
            current.Position.Y = (Single)(point.Y + (dy / d) * sr);
        }
    }

    if (x < left && y > bottom)
    {
        point = new Vector2(left, bottom);
        if (current.HasOverlap(point))
        {
            hasAnyOverlap = true;

            var dx = current.Position.X - point.X;
            var dy = current.Position.Y - point.Y;
            var sr = current.Radius;
            var d = Math.Sqrt(dx * dx + dy * dy);
            current.Position.X = (Single)(point.X + (dx / d) * sr);
            current.Position.Y = (Single)(point.Y + (dy / d) * sr);
        }
    }

    if (x > right && y > bottom)
    {
        point = new Vector2(right, bottom);
        if (current.HasOverlap(point))
        {
            hasAnyOverlap = true;

            var dx = current.Position.X - point.X;
            var dy = current.Position.Y - point.Y;
            var sr = current.Radius;
            var d = Math.Sqrt(dx * dx + dy * dy);
            current.Position.X = (Single)(point.X + (dx / d) * sr);
            current.Position.Y = (Single)(point.Y + (dy / d) * sr);
        }
    }
    #endregion Corners

    #region Edges

    if (x > left && x < right && y < top)
    {
        hasAnyOverlap = true;
        if (y + current.Radius > top)
            current.Position.Y = top - current.Radius;
    }

    if (x > left && x < right && y > bottom)
    {
        hasAnyOverlap = true;
        if (y - current.Radius < bottom)
            current.Position.Y = bottom + current.Radius;
    }

    if (y > top && y < bottom && x < left)
    {
        hasAnyOverlap = true;
        if (x + current.Radius > left)
            current.Position.X = left - current.Radius;
    }

    if (y > top && y < bottom && x > left)
    {
        hasAnyOverlap = true;
        if (x - current.Radius < right)
            current.Position.X = right + current.Radius;
    }

    #endregion Edges
}