Canvas with static content and items - wpf

Question

I have a Canvas which contains static elements - those elements use binding to draw it in the right places. Now I need to draw other elements depending on items in a collection. I want to use ItemsControl, but I don't know how to do it correctly. My current pseudo-code:
<UserControl.Resources>
<RectangleGeometry x:Key="MyGeometry1">
<RectangleGeometry.Rect>
<MultiBinding Converter="{StaticResource RectConverter}">
<Binding Path="ActualWidth" ElementName="m_Canvas" />
<Binding Path="ActualHeight" ElementName="m_Canvas" />
</MultiBinding>
</RectangleGeometry.Rect>
</RectangleGeometry>
</UserControl.Resources>
<Canvas x:Name="m_Canvas">
<!-- "static" content -->
<Line x:Name="Line1" X1="{Binding Line1X1}" X2="{Binding Line1X2}" Y1="{Binding Line1Y1}" Y2="{Binding Line1Y2}"/>
<Line X1="0" X2="{Binding ActualWidth, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Canvas}}}" Y1="0" Y2="0">
<Path Fill="#35A500"
Opacity="0.15">
<Path.Data>
<GeometryGroup FillRule="EvenOdd">
<StaticResource ResourceKey="MyGeometry1" />
</GeometryGroup>
</Path.Data>
</Path>
<Line X1="{Binding Items[0].X1}" X2="{Binding Items[0].X2}" Y1="{Binding Items[0].Y1}" Y2="{Binding Items[0].Y2}"/>
<Line X1="{Binding Items[1].X1}" X2="{Binding Items[1].X2}" Y1="{Binding Items[1].Y1}" Y2="{Binding Items[1].Y2}"/>
<Line X1="{Binding Items[2].X1}" X2="{Binding Items[2].X2}" Y1="{Binding Items[2].Y1}" Y2="{Binding Items[2].Y2}"/>
</Canvas>
I tried something like this:
<ItemsControl ItemsSource="{Binding Items}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas>
<!-- "static" content -->
<Line x:Name="Line1" X1="{Binding Line1X1}" X2="{Binding Line1X2}" Y1="{Binding Line1Y1}" Y2="{Binding Line1Y2}"/>
<Line X1="0" X2="{Binding ActualWidth, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Canvas}}}" Y1="0" Y2="0">
</Canvas>
</ItemsPanelTemplate>
<!-- (...) other code -->
</ItemsControl>
But I have an error:
Error XDG0062 Cannot explicitly modify Children collection of Panel used as ItemsPanel for ItemsControl. ItemsControl generates child elements for Panel.
I understand that is because I put Line1 inside Canvas but how to make such Canvas with some kind static content and also as a container for items?

Answer 1

The "static content" could be put into another Canvas above or below the ItemsPresenter in the ControlTemplate of the ItemsControl:
<ItemsControl ItemsSource="{Binding Items}">
<ItemsControl.Template>
<ControlTemplate TargetType="ItemsControl">
<Grid>
<Canvas>
<!-- "static" content -->
</Canvas>
<ItemsPresenter/>
</Grid>
</ControlTemplate>
</ItemsControl.Template>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Canvas/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>