mORMot Open Source

I found an oddity in code where I accessed VCLCanvasSize before VCLCanvas. Since the VCLCanvas is lazily created on demand, this scenario leads to GetVCLCanvasSize accessing fVCLCanvasSize before it has been initialised. I worked around this by making sure that I access VCLCanvas before VCLCanvasSize, but I think that this protection should be implemented inside SynPdf.

I'm trying to implement a "multiple pages per sheet" feature for my PDF output.  I'm currently rendering a single metafile to each page of the PDF document, calling TPdfCanvas.RenderMetaFile to achieve that.  It works a treat.

However, I'm not trying to call this function multiple times on the same page with no luck.  I'm seeing nothing at all in the generated PDF, or sometimes just a couple of parts of one of the metafiles.  But certainly not multiple metafile graphics around the page.

Before I carry on, is this something that I can expect to do, or do I need to find another approach?  I know that I can create my own metafile canvas, render my metafiles to that canvas, and finally render the composite metafile to the PDF document with a single call to TPdfCanvas.RenderMetaFile.  I was hoping to avoid having to use that extra metafile to prepare my pages.

If I should be able to call TPdfCanvas.RenderMetaFile multiple times per page, and you'd like to dig into this, I'll prepare a reproduction of the issue.  I've not done that yet because it would take a little while to extract it from my complex application code.  And I didn't want to spend that time if the answer was a simple, "this can never work, do it a different way".

Consider the following program:

program PdfTest;

{$APPTYPE CONSOLE}

uses
  System.SysUtils,
  System.Classes,
  Winapi.Windows,
  Vcl.Graphics,
  SynCommons in 'Synopse\SynCommons.pas',
  SynLZ in 'Synopse\SynLZ.pas',
  SynPdf in 'Synopse\SynPdf.pas';

var
  Doc: TPdfDocument;
  Page: TPdfPage;
  Metafile: TMetafile;
  Canvas: TMetafileCanvas;
begin
  // create test metafile
  Metafile := TMetafile.Create;
  Metafile.SetSize(700, 700);
  Canvas := TMetafileCanvas.Create(Metafile, GetDC(0));
  Canvas.MoveTo(0, 0);
  Canvas.LineTo(700, 700);
  Canvas.MoveTo(0, 700);
  Canvas.LineTo(700, 0);
  Canvas.Free;

  // create page in portrait orientation, and render metafile to it
  Doc := TPdfDocument.Create;
  Doc.DefaultPaperSize := psA4;
  Page := Doc.AddPage;
  Page.PageLandscape := False;
  Doc.Canvas.RenderMetaFile(Metafile);
  Doc.SaveToFile('_portrait.pdf');

  // same again, but with landscape orientation
  Doc := TPdfDocument.Create;
  Doc.DefaultPaperSize := psA4;
  Page := Doc.AddPage;
  Page.PageLandscape := True;
  Doc.Canvas.RenderMetaFile(Metafile);
  Doc.SaveToFile('_landscape.pdf');
end.

This emits two PDF files that are meant to contain a simple cross.  The portrait orientation version comes out correctly.  The landscape orientation does not.

I tracked this down to the fact that TPdfCanvas.SetPage is called from AddPage.  And this caches the height of the the page:

procedure TPdfCanvas.SetPage(APage: TPdfPage);
begin
  FPage := APage;
  FPageFontList := FPage.GetResources('Font');
  FContents := TPdfStream(FPage.ValueByName('Contents'));
  FHeight := FPage.GetPageHeight;  <-----  UH OH!
  FFactor := 72/FDoc.FScreenLogPixels; // PDF expect 72 pixels per inch
end;

Then when we subsequently change orientation, the page height is changed, but FHeight is not updated.

I guess I can solve my problem by throwing in a call to TPdfCanvas.SetPage immediately before I call RenderMetafile.  Is that what I am supposed to do?  Is there a better way to solve my problem?  Is the library behaving as designed?  Do you mean to cache FPage.GetPageHeight and then not update it later?

Thanks!