Review Request 130218: Print via QPrinter when rasterizing and printing annotations

[Oliver Sander]

> On Aug. 6, 2017, 3:17 p.m., Albert Astals Cid wrote:
> > Rasterizing usually makes stuff look quite bad (because the wrong resolution is chosen) , have you tried printing text or things with sharp lines?
> 
> Oliver Sander wrote:
>     Yes I tried that, and it looks very good.  It looks so good I wasn't even able to tell that it was rasterized before printing.  The resolution chosen by the code adapts to the printer
>     
>          QImage img = pp->renderToImage(  printer.physicalDpiX(), printer.physicalDpiY() );
>     
>     and I guess it must be pretty large when printing to an actual printer.
> 
> Albert Astals Cid wrote:
>     So we will kill cheap printers/computers by using lots of memory? Can you try to see how much memory is used printing an A4 page? Also make sure that printing N pages doesn't need N times the memory (i guess using heaptrack or similar)
> 
> Oliver Sander wrote:
>     Quick first results: printer.physicalDpiX() returns a value of 1200, both for printing to my office printer and for printing to a file.  An A4 printout results in a 9921 x 14032 bitmap; the corresponding file size is 804 KB (greyscale).  Testing the actual memory consumption will take me a bit more time.
>     
>     I don't actually care about the exact resolution.  If you say "bah, just hard-code 72dpi there" that's fine with me.
> 
> Albert Astals Cid wrote:
>     >  9921 x 14032 bitmap
>     
>     Does that mean that you need 9921x14032x32 bits in memory? That's around 530 MB, right? I guess it's not horrible in todays big scheme of things if it doesn't get multiplied by the number of pages.
> 
> Oliver Sander wrote:
>     I now tried to measure the heap consumptions using valgrind/massif.  I printed to files exclusively, to save some trees.
>     
>     If I read the massif output correctly, the new code needs about 1GB of heap space to print A4 pages, and that is independent of the number of pages.
>     
>     On the other hand, printing an A0-size poster fails with the friendly message "Bogus memory allocation size".  Not really surprising: that would need an enormous amount of memory.
> 
> Albert Astals Cid wrote:
>     > On the other hand, printing an A0-size poster fails with the friendly message "Bogus memory allocation size".  Not really surprising: that would need an enormous amount of memory.
>     
>     I'm not sure i'm ok with that.
>     
>     Why are we discussing this instead of printing pdf directly?

> I'm not sure i'm ok with that.

Okay.  I changed the patch to always use 300dpi when the platform is not Windows.  That is the resolution that was used previously (see poppler/PSOutputDev.cc:1260). Therefore, this patch does not bring functional changes anymore: with and without the patch, the rasterization resolution is printer.physicalDpiX() for Windows, and 300 for all others.

> Why are we discussing this instead of printing pdf directly?

- Printing the pdf does not rasterize it, but this patch is about rasterized printing
- The new code does not involve the detour via postscript
- It does not rely on CUPS tools like 'lpr'
- It is platform-independent (exception: the rasterization resolution)
- It is short and elegant
- It fixes at least one bug: greyscale printing

Follow-up patches are in the pipeline.


- Oliver


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On Aug. 9, 2017, 8:58 p.m., Oliver Sander wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/130218/
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> 
> (Updated Aug. 9, 2017, 8:58 p.m.)
> 
> 
> Review request for Okular.
> 
> 
> Repository: okular
> 
> 
> Description
> -------
> 
> When the users chooses to print with rasterization and annotations, it is easy to print directly to a QPrinter, rather than converting to PostScript and then using CUPS tools.  The code for it was already there, but it was hidden behind an #ifdef Q_OS_WIN. This patch enables it for all plattforms.  If nothing else, it will make an interesting debugging tool, because it allows to bypass the postscript & cups toolchain from the GUI. This may allow to track down some of the numerous my-printer-settings-are-getting-ignored bugs.
>     
> Incidentally, this patch does fix at least one bug for me: Without it, my printer will happily ignore the 'print in grayscale' button.  With the patch, that button is suddenly honoured.
> 
> This patch is a part of https://git.reviewboard.kde.org/r/130055/ .  I post it here separately because I am not sure anymore whether the other stuff in that larger patch is a good idea.
> 
> 
> Diffs
> -----
> 
>   generators/poppler/generator_pdf.cpp 42ccb3a26 
> 
> Diff: https://git.reviewboard.kde.org/r/130218/diff/
> 
> 
> Testing
> -------
> 
> Printed a few test sheets, to a printer and a file.
> 
> 
> Thanks,
> 
> Oliver Sander
> 
>

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