You raise a very valid point. Currently we are indeed unable to fulfill the scenario described, however, it is of core importance for RadChartView. We are definitely commiting to providing this experience and I can also use the opportunity to share with you how we envision this hapening at the moment:
We will create a UI virtualization mechanism for linear charts which will only display the part of the line which is actually visible during zooming and scrolling. Let's say you have bound the chart to 1,000,000 records and have zoomed a small part of say 1000 points. You will still be able to use smooth scrolling and zoom the chart as usual, however, only the visible part of the line will be rendered meaning you will get a polyline segment with 1000 points in that particular case.
We will also consider implementing a mechanism to call back to ChartDataSource and adjust the sampling threshold mechanism in accordance with the zoom level. This means that once you zoom, the sampling will change and the ChartDataSource will provide a continuously more detailed view of the data, while keeping performance good using UI Virtualization.
We have our hopes that this will happen in time for the Q1 release which will also mark the official release of RadChartView.
Thank you again for your feedback and feel free to write back to me should you have any ideas, problems, concerns with how RadChartView handles large amounts of data.
the Telerik team
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