Steema Central

SteveP wrote:I ahve not looked in the source code, but does the Nearest Point tool always begin its search from the beginning or end of the data array ? If not, it might be faster to begin from the previous nearest point index and search away from that in both directions. This assumes linearity in values.

I have tried this solution and effectively performances are highly improved. But in this case, the circle around focused point is not painted. In our application, we always need a black circle around nearest point. So, do you have another solution to propose?

procedure TForm1.FormCreate(Sender: TObject);
begin
  Series1.FillSampleValues(10000);

  With ChartTool1 do
  begin
    FullRepaint:=false;
    Pen.Color:=clBlack;
  end;
end;

Narcis, Does Steema expects to deliver a new release fixing this performance defect?

9336299 wrote:Thanks SteveP,

You are right. I have looked in source code TNearestTool.GetNearestPoint and TNearestTool.ChartMouseEvent and it seems that search is always performed from beginning to end of series each time user moves mouse in chart. It is not acceptable for performance when we have more than 20000 data in series. Moreover, search algorithm in GetNearestPoint is basic. Why this GetNearestPoint method does not use a dichotomy search algorithm or more advanced search algorithm? Algorithm may be different for each kind of series to improve performance in different cases.

Code: Select all

class Function TNearestTool.GetNearestPoint(Series:TChartSeries; X,Y:Integer; IncludeNulls:Boolean):Integer;
var t      : Integer;
    Dif    : Integer;
    Dist   : Integer;
    tmpMin : Integer;
    tmpMax : Integer;
    tmpX   : Integer;
    tmpY   : Integer;
    tmpZList : TChartValueList;
    tmpZ   : Integer;
begin
  result:=-1;
  Dif:=10000;

  if TeeGetFirstLastSeries(Series,tmpMin,tmpMax) then
  begin
    tmpZList:=Series.GetYValueList('Z'); // 7.0

    for t:=tmpMin to tmpMax do { <-- traverse all points in a Series... }
    if IncludeNulls or (not Series.IsNull(t)) then // 7.0
    begin
      { calculate position in pixels }
      tmpX:=Series.CalcXPos(t);
      tmpY:=Series.CalcYPos(t);

      if Series.HasZValues then
      begin
        tmpZ:=Series.ParentChart.Axes.Depth.CalcPosValue(tmpZList.Value[t]);

        with Series.ParentChart.Canvas.Calculate3DPosition(tmpX,tmpY,tmpZ) do
        begin
          tmpX:=X;
          tmpY:=Y;
        end;
      end;

      if PointInRect(Series.ParentChart.ChartRect,tmpX,tmpY) then { 5.01 }
      begin
        { calculate distance in pixels... }
        Dist:=Round(TeeDistance(X-tmpX,Y-tmpY));

        if Dist<Dif then { store if distance is lower... }
        begin
          Dif:=Dist;
          result:=t;  { <-- set this point to be the nearest... }
        end;
      end;
    end;
  end;
end;

procedure TNearestTool.ChartMouseEvent(AEvent: TChartMouseEvent;
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  inherited;

  if (AEvent=cmeMove) and Assigned(Series) then
  begin
    if not FullRepaint then PaintHint;
    Point:=GetNearestPoint(Series,X,Y);
    IMouse:=TeePoint(x,y);
    if not FullRepaint then PaintHint;
    if Assigned(FOnChange) then FOnChange(Self);
    if FullRepaint then Repaint;
  end;
end;

Narcis, Does Steema expects to deliver a new release fixing this performance defect?

Regards
Gerald