In order to highlight the item Rectangle in the PointTemplate based on a condition you can use its Stroke property for example. Or you can change its color as demonstrated in the code snippet from your last reply. Also, another approach of setting the colors in the PointTemplate is instead of using data triggers to binding the Fill property directly to the property from the model (DataItem.IsPass or IsSelected) with an IValueConverter.
About stretching the element in the PointTemplate, since all chart elements are drawn and positioned in a Canvas you will need to manually recalculate the size of the Rectangle element each time the chart's layout is updated. In your case you can do it when the PanOffsetChanged
events of the chart are fired.
As for accessing the relative parent point template, I am not sure that I understand what this means. Can you please clarify it for me? Also, if you want to change something in the elements in the PointTemplate at runtime you can bind them to the view model of the data point. If you want to get the data point under the mouse you can use the Conversion API
Do you need help with upgrading your AJAX, WPF or WinForms project? Check the Telerik API Analyzer
and share your thoughts.