public class ProducerWrapPanel : Panel
{
    protected override Size MeasureOverride(Size constraint)
    {
        foreach (UIElement element in base.InternalChildren)
        {
            element.Measure(constraint);
        }

        return constraint;
    }

    protected override Size ArrangeOverride(Size arrangeBounds)
    {
        int count;
        double top;
        double left;

        count = 1;
        top = 0;
        left = 0;

        foreach (UIElement element in base.InternalChildren)
        {
            element.Arrange(new Rect(left, top, element.DesiredSize.Width, element.DesiredSize.Height));

            if ((float)count / 4.0 == count / 4)
            {
                left = 0;
                top = top + element.DesiredSize.Height;
            }
            else
            {
                left = left + element.DesiredSize.Width;
            }

            count++;
        }

        return arrangeBounds;
    }
}