Setting the Scrollbar Thumb size

Question

I am attempting to work out the algorithm associated with sizing of the WPF Scrollbar thumb element.

The thumb element can be sized using the Scrollbar.ViewportSi

Answer 1

Scrollbar thumb size for UWP:

    static void SetViewportSize(ScrollBar bar, double size)
    {
        var max = (bar.Maximum - bar.Minimum);
        bar.ViewportSize = size / (max - size) * max;
        bar.IsEnabled = (bar.ViewportSize >= 0 &&
            bar.ViewportSize != double.PositiveInfinity);
        InvalidateScrollBar(bar);
    }

    static void InvalidateScrollBar(ScrollBar bar)
    {
        var v = bar.Value;
        bar.Value = (bar.Value == bar.Maximum) ? bar.Minimum : bar.Maximum;
        bar.Value = v;
    }