Can I make WPF set IsMouseOver for both the covering and covered element?

Question

The simplified example this; picture a Venn diagram made from two elements, A and B, that overlap. If I mouse over (A AND (NOT B)) all of A lights up. If I mouse over (B AND (NO

Answer 1

You can do manual hit testing using VisualTreeHelper. This can go into a MouseMove handler on some parent object. Here I'm assuming a Venn diagram made of ellipses named RedCircle and BlueCircle:

bool overRed = false;
bool overBlue = false;
if (BlueCircle.IsMouseOver || RedCircle.IsMouseOver)
{
    HitTestParameters parameters = new PointHitTestParameters(e.GetPosition(RedCircle));
    VisualTreeHelper.HitTest(RedCircle, new HitTestFilterCallback(element => HitTestFilterBehavior.Continue), result =>
    {
        if (result.VisualHit == RedCircle)
            overRed = true;
        return HitTestResultBehavior.Continue;
    }, parameters);

    parameters = new PointHitTestParameters(e.GetPosition(BlueCircle));
    VisualTreeHelper.HitTest(BlueCircle, new HitTestFilterCallback(element => HitTestFilterBehavior.Continue), result =>
    {
        if (result.VisualHit == BlueCircle)
            overBlue = true;
        return HitTestResultBehavior.Continue;
    }, parameters);
}