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HitTest accuracy


peterz
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I'm trying to use the HitTest method to detemine the chart object the mouse is over while dragging something onto a chart. The results are not what I expected. Here is my scenario using the ChartFx MouseEvents sample:

1. Set AllowDrop = true in Form1_Load

2. Add this code to Form1:

protected override void OnDragOver(DragEventArgs e)

{

Point point = chart1.PointToClient(new Point(e.X, e.Y));

HitTestEventArgs ht = chart1.HitTest(point.X, point.Y);

System.Diagnostics.Debug.WriteLine(string.Format("HitType={0} ({1}, {2})", ht.HitType, ht.AbsoluteLocation, point));

e.Effect = DragDropEffects.Copy;

}

3. Run the sample.

4. Move the mouse (no drag yet) to the bottom left corner of the axes intersection (ie. 0, 0 -- the origin).

5. Note the Mouse Position value, I see 67,264 and the Chart Element is Axis: Main X Axis

6. Now drag some data (ie. text from any drag enabled source) to the same point -- don't drop it, just move the drag cursor so it points to the origin.

7. Note the debug output in the IDE, I see x=74, y=271

The location of point and ht.AbsoluteLocation are always off by 7 pixels. What am I doing wrong with the call tto HitTest?

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Only a small change needs to be made:

Replace:

HitTestEventArgs ht = chart1.HitTest(point.X, point.Y);

 with:

HitTestEventArgs ht = chart1.HitTest(point.X, point.Y,true);

The true at the end is for Absolute position, otherwise the position is assumed to be inside the chart's "Drawing Area" which excludes the border, toolbar, legend box and DataGrid.

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