canvas does not support drawing

Version: wPDF 2 Standard
Downloaded: 30/4/04
I am rolling out a survey generation system nationally to primary schools, and it is working fine - (excellent PDF generation, thank you!)
I am using the canvas property to generate bespoke surveys based on database values, and all was fine BUT on the seventh test site, on an old Pentium II machine, I am getting the above error ("canvas does not support drawing"), followed by exceptions (which may be mine - the software seemed reliable enough not to test for all possibilities).
All other test sites have been fine.
Are there minimum system requirements, particulr versions of windows, system DLLs etc or am I doing something wrong?
Many thanks
Martin Casey

Is it possible to be more specific about resource requirements, in terms of how hungry creating a wPDF is on memory and handles.
All my forms apart from the app's main form and data module are created/freed on the fly.
Could you please glance at the code segment below (Delphi - Pascal), and direct me towards any code problems?
For example, the (approx 800K) embedded font file - does that use a correspondingly larger amount of memory than the (40K) non embedded font PDFs?

The code I am using is as follows:
// Some of the PDFs require unusual font: HelveticaNeue-Bold, so
if (UsingHelveticaNeueBold) then // not likely to be on end user PC
PDFPrinter.FontMode := wpEmbedSubsetTrueType_UsedChar
else
PDFPrinter.FontMode := wpUseTrueTypeFonts;

PDFPrinter.BeginDoc;
Res := Screen.PixelsPerInch;

// For each page: Typically 10 - 30 pages of text, rectangles etc - plus
// an initial rectangle the full page size to colour it appropriately

PDFPrinter.StartPage(Round(21/2.54*res), Round(29.7/2.54*res), res,
hCanvas := PDFPrinter.Canvas;

// Then body of page, with lots of calls to :
// hCanvas.TextOut
// hCanvas.Rectangle
// hCanvas.RoundRect

PDFPrinter.EndPage;

// Finally,
PDFPrinter.EndDoc;

Hi, and thank you for your last prompt reply.
I'm sure the problem is likely to be to do with resources, as you say.
However, it crashes on the first canvas.textout procedure, even with completely stripped down code.
I have a very simple test harness program - a form with a TWPPDFPrinter (all default properties), and a button which calls the following code:

//=================================
procedure TForm1.BitBtn1Click(Sender: TObject);
var
res : Integer;
begin
WPDF_Start('mycode','myserial');
with WPPDFPrinter1 do
begin
FontMode := wpUseTrueTypeFonts;
Filename := 'C:\xPDFx.pdf';
BeginDoc;
Res := Screen.PixelsPerInch; // returns 96
StartPage(Round(21/2.54*res), Round(29.7/2.54*res), res, res, 0);
Canvas.TextOut(100, 100, 'Hello PDF World.');
// The above statement generates the exception "Canvas does not allow drawing"
EndPage;
EndDoc;
end;
end;
//=================================

The machine this is happening on is a PC purchased in the year 2000, with spec as follows:
Athlon AMD 800MHz Processor
200MHz Motherboard
128MB SDRAM
Windows Me Millennium Edition 4.90.3000

The version of wPDF200A.dll is 2.4.0.7

The Gold Master version of the product needs to be delivered to the Govt Department (DfES) next Friday (18/05/04)!
Any suggestions?
Regards
Martin

Thanks Julian
The metafile is created fine.
(I can also textout to the canvas on a printer, even though there is no printer connected to the test machine, but a default printer is
setup. The textout works, and the printer.enddoc displays then correctly displays the printer device's error dialog).

The CanvasReference is set to the default wprefScreen.

Additional info - thinking outloud:
I think the problem probably only happens with Windows 98 & Me. Thinking about GDI resources, whatever RAM is avail these only have 32MB GDI heap. However, the DC for the metafile, the printer and even a paintbox I tried are all clearly allocated OK.
SO - I still don't think this is the problem, as it is happening as soon as the first textout statement is encountered.

So I reckon the device context of the canvas isn't valid for some other reason.

Any ideas?
(I'm getting very worried about delivery)
Regards
Martin

Hi Julian - Update
I think I have found a solution - it is to do with the initialisation of the FReferenceDC variable in your WPPDFR1 unit's GetCanvas function. I tried doing a DC := Canvas.Handle and this also gave the same error. The error was generated at the
FCanvas := TMetafileCanvas.Create(FMetafile, FReferenceDC);
statement, so as the only difference between the GetCanvas function's TMetafileCanvas.Create and the one that worked was the FReferenceDC.
Setting this to zero then allows canvas drawing. Ureka!

The altered code in WPPDFR1 is shown below:

function TWPCustomPDFExport.GetCanvas: TCanvas;
var
currX, currY: Integer;
DC: HDC;
begin
if FCanvas = nil then
begin
FMetafile := TMetafile.Create;
FMetafile.MMWidth := Round(FLastWidth / Fpage_xres * 2540); // 1/100 mm !
FMetafile.MMHeight := Round(FLastHeight / Fpage_yres * 2540);
FMetafile.Enhanced := TRUE;
FCanvas := TMetafileCanvas.Create(FMetafile, 0{FReferenceDC}); // Probem here!
FCanvas.Font.PixelsPerInch := Fpage_yres;
FCanvas.Brush.Style := bsClear;
DC := FCanvas.Handle;
currX := GetDeviceCaps(DC, LOGPIXELSX);
currY := GetDeviceCaps(DC, LOGPIXELSY);
SetMapMode(DC, MM_ANISOTROPIC);
SetWindowExtEx(DC, Fpage_xres, Fpage_yres, nil);
SetViewPortExtEx(DC, currX, currY, nil);
SetViewPortOrgEx(DC, 0, 0, nil);
SetWindowOrgEx(DC, 0, 0, nil);
end;
Result := FCanvas;
end;

Can you please let me know the implications of changing this value - I have not tested it on multiple page documents etc.
I would much rather have a fix that you are confident in.

Thanks,
Martin