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Another store from the trenches: GDI vs PDF

2018-07-06 18:31  gdipdf  coding dagboek delphi werk  [permalink]

One of the great things about Delphi is this object-oriented way of manipulating things called the Visual Component Library. There's much more to it than that, but in a sense you could describe it as a wrapper around Windows API's. One of these is GDI, it's old but it's still there and used for graphics and text-layout. It was born, way back when, from the idea of What You See Is What You Get (WYSIWYG) taken even further and that the same program logic could work for display on screen and writing to a printer. Delphi's VCL declares the TCanvas class you can use to design the output, and wether you pass a Printer.Canvas, Screen.Canvas, Form.Canvas or Bitmap.Canvas shouldn't really matter. This works great for forms and reports.

But in the printing business, there's much more than forms and reports to put on paper. Over there the PDF reigns supreme. It performs a similar task, but originated out of a very different set of parameters. A big module we created of the production software at work generates them according to specifications. How this works is very different as the components that make up a PDF document are constructed one by one and this doesn't look like the work you normally would do with a TCanvas instance.

But now and again these two worlds need to bridge over to eachother. One day I had to keep automatic PDF archive copies of some reports, and discovered the great SynPDF project from the same people that created the mORMot framework. It offers a TCanvas instance (TPdfDocumentGDI.VCLCanvas) that you can pass to code that knows what to with a TCanvas reference.  It works great.

I haven't needed to think about crossing the two the other way round, but recently I noticed a collegue did, and he also found a simple straight-forward solution for the problem: You can just ask the PDF reader on the system to render a PDF to a printer. It's as simple as starting a process with:

"C:\Program Files (x86)\Adobe\Acrobat Reader DC\Reader\AcroRd32.exe" /n /t "<document to print>" "<printer name>"


"C:\Program Files (x86)\SumatraPDF\SumatraPDF.exe" -print-to "<printer name>" "<document to print>" 

This works just great and even doesn't add too much code to your program. You may need to include the PDF viewer installer with your installer, but that's a minor issue and perhaps not even required as most people have a PDF reader installed by default.

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