[SOLVED] value of hinttool.NearestGraphPoint.y is not exactly the
original value
lazarus / 55-TAChart

----------------------------------------------------------------------
kinlion · 2018-12-07 05:40

I add some LineSeries to a Chart, and show hint when mouse on a data
point.
Similar to wp said in the post
https://forum.lazarus.freepascal.org/index.php/topic,34723.0.html
I write:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TfrmLTPlanManager.ChartToolset1DataPointHintTool1Hint(  ATool:
TDataPointHintTool; const APoint: TPoint; var AHint: String);var 
hinttool: TDataPointHintTool;  ser: TLineSeries;begin  hinttool :=
TDataPointHintTool(ATool);  ser := TLineSeries(hinttool.Series);    
// this is the clicked series  if ser = nil then    exit;   AHint :=
Format('%6d日 %s %.0n支',      [       
trunc(hinttool.NearestGraphPoint.X),        ser.Title,       
hinttool.NearestGraphPoint.y      ]);end; 
However, the hint value from hinttool.NearestGraphPoint.y is not the
original value.

Why?

----------------------------------------------------------------------
wp · 2018-12-07 09:34

Oh, I was not aware of this. It is because the "NearestGraphPoint" is
calculated back from the screen pixels of the data point which leads
to some inaccuracies. I don't know why it is made like this, probably
because the corresponding TDataPointTool method is very general and
must work also for series which do not require discrete listed data
(such as TFuncSeries).

A better way is to directly read the x,y values from the series or the
chart source. If your data are stored in the internal listsource of
the lineseries you can simply call ser.XValue[index] and
ser.YValue[index] where index is the series point index returned by
ther chart tool (ser.PointIndex):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.ChartToolset1DataPointHintTool1Hint(ATool: TDataPointHintTool; 
const APoint: TPoint; var AHint: String);var  ser: TLineSeries; 
index: Integer;begin  if (ATool = nil) or (ATool.Series = nil) then  
AHint := ''  else begin    ser := TLineSeries(ATool.Series);    index
:= ATool.PointIndex;    AHint := Format('Series "%s":' + LineEnding +
'  x = %.3f' + LineEnding + '  y = %.3f',      [ser.Title,
ser.XValue[index], ser.YValue[index] ]);  end;end;  If data are
provided by an external chartsource you query them from there, again
ATool.PointIndex is the index of the data point.

You wrote somewhere that you have the data in an array. Then you
probably use a TUserDefinedChartSource to link to array to the series.
In this case you can call the OnGetChartDataItem event handler to find
the x,y values.

----------------------------------------------------------------------
kinlion · 2018-12-07 15:57

Quote from: wp on December 07, 2018, 10:34:58 amA better way is to
directly read the x,y values from the series or the chart source. If
your data are stored in the internal listsource of the lineseries you
can simply call ser.XValue[index] and ser.YValue[index] where index is
the series point index returned by ther chart tool (ser.PointIndex):

ser.PointIndex helps to resolve the problem.
Thanks wp

btw, how to mark this topic as RESOLVED ?

----------------------------------------------------------------------
wp · 2018-12-07 16:17

Edit the title of the first post and add "[SOLVED]" in front of the
title.