Rendering TBIChart to PNG

[De-Novo-Research]

Hello.

If I use the code below, I can save any TChart to PNG. Even one I create programmatically and has never been actually shown onscreen.

However, when I use this method on TBIChart.Chart, without the TBiChart being shown onscreen, the resulting PNG just has a black border and nothing else. I cannot see why this should not work, since TBITChart is just a TChart descendent.

If I show the TBiChart onscreen and then call the code below on the BiChart1.Chart, the resulting PNG is fine. Is there some method I can call to force the TBiChart.Chart to update itself so it can render to PNG even though it has not been shown on screen yet?

  TChartHelper=class helper for TChart
  public
    procedure SaveToPNG(const aFileName:string; const aWidth:integer=-1; const aHeight:integer=-1);
  end;



implementation

procedure TChartHelper.SaveToPNG(const aFileName:string; const aWidth:integer=-1; const aHeight:integer=-1);
var
  PNGExport: TPNGExportFormat;
begin
  PNGExport := TPNGExportFormat.Create;
  try
    PNGExport.Panel := self;
    if aWidth>0 then
      PNGExport.Width := aWidth
    else
      pngExport.Width := self.Width;

    if aHeight>0 then
      PNGExport.Height := aHeight
    else
      pngExport.Height:=self.Height;

    PNGExport.SaveToFile(aFileName);
  finally
    PNGExport.Free;
  end;
end;

[davidberneda]

Yes you're right, this is another thing that should be improved, right now the "hack" is to force passing a WM_PAINT message to make the chart to fill its series:

SendMessage(BIChart1.Handle,WM_PAINT,0,0);
BIChart1.Chart.SaveToPNG('c:\test.png');

Delaying series creating until the very ultimate painting was done to fix some bug related to loading the BIChart (and it child chart) from the DFM form. It was too early to create the chart in the Loaded step, so the easy thing was to delay until repaint, but now it hurts doing anything with a non-painted-yet chart.

I'll review and try to remove that delay, identifying the needs.

[De-Novo-Research]

This does not quite work because TBiChart has no parent window in my case. Neither does calling

SendMessage(FBIChart.Chart.Handle,WM_PAINT,0,0);

I still get the same error that there is no parent window.

[davidberneda]

Ah ! No Parent, no Handle !
Ok, I've made a special method to allow refreshing a non-parented chart that has never been painted.

  BIChart1.CheckPendingData;
  BIChart1.Chart.SaveToPNG('c:\test.png');

Added here: 08ea5ce

Its not very elegant, calling that method should be never mandatory, but so far it fixes the problem.
As soon the chart is painted at least once, all is fine.