PowerToys/tools/FancyZone_HitTest/FancyZone_HitTest/MainWindow.xaml

<Window
    x:Class="FancyZone_HitTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:FancyZone_HitTest"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="1024"
    Height="768"
    mc:Ignorable="d">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition Width="200" />
        </Grid.ColumnDefinitions>
        <Grid Name="hitTestGrid" MouseMove="Grid_MouseMove">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>


            <Rectangle
                Name="a"
                Grid.Column="0"
                Fill="#ff0000" />
            <Rectangle
                Name="b"
                Grid.Column="1"
                Fill="#00ff00" />
            <Rectangle
                Name="c"
                Grid.Column="2"
                Fill="#0000ff" />
            <Rectangle
                Name="d"
                Grid.ColumnSpan="3"
                Width="550"
                Height="500"
                Fill="#aabbff" />
            <!--  Height="600"  -->
            <Rectangle
                Name="f"
                Grid.ColumnSpan="3"
                Width="400"
                Height="400"
                Fill="#aabbff" />
            <Rectangle
                Name="e"
                Grid.ColumnSpan="3"
                Fill="Orange" />

        </Grid>
        <StackPanel Grid.Column="1">
            <TextBlock>Calculations</TextBlock>
            <TextBlock x:Name="itemsHit" />
        </StackPanel>
    </Grid>
</Window>