hoakley February 23, 2019 General, Macs, Technology

Synchronised Scrolling: a brief movie on PDF

A few days ago, I reported a bug in the handling of PDF documents in macOS Mojave 10.14.3, which linked open windows together so that they bizarrely scrolled in unison.

Here is a demonstration in a screenshot movie:

You are watching six quite different PDF documents, each open in its own window in my free PDF reader Podofyllin, which uses vanilla macOS features (PDFKit) to handle and display those documents. I have provided source code to a very similar app which you can study and build for yourself here: BasicPDFViewer 1.0b3.

In this demonstration, the centre window in the lower row is at the front. I then use the cursor keys to step through its pages. As the selected thumbnail view changes in that window, the bug changes the selected page in all the other five windows. I step down through the document, and back up again, with every window changing in unison.

This is entertaining viewing, so long as you aren’t sensitive to screen motion, but makes the thumbnail views in macOS useless. Every app which displays PDF thumbnails – including Apple’s own Preview – therefore has to use its own workaround, because Apple doesn’t apparently consider that fixing this bug in PDFKit is important enough.

Please share this widely if you feel that, in return for Apple’s premium prices, we should get premium products, without such gross bugs.

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1

Michele Galvagno on February 23, 2019 at 8:12 am

I really don’t know what’s the problem with PDFs and why they may be so complicated.
Yesterday I wanted to create a high-quality PDF via Acrobat Pro (don’t know if that is even a function that works) for professional printing by merging multiple PDFs (something that I normally do with Preview by dragging documents in the thumbnail view).

The customer who received the PDF opened it in Acrobat and, while the file was looking perfect —it was a music score— the printer spat out notes without noteheads…
Opening the same in Preview solved…

Still scratching my head now…

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- 2
  
  hoakley on February 23, 2019 at 9:25 am
  
  The problem with PDF is that it’s so complicated. Not one but two general ISO standards, each of which is around 1000 pages. And they build on a long series of Adobe’s ‘standards’ from 1.3 (and earlier) through to 1.7. Then each has to be implemented by someone different: the app which writes the PDF takes one view, then it’s displayed on screen by a reader app which converts the content into Quartz 2D graphics, which are rendered by macOS. When you print, the app says how to convert the graphics into another PDF, which is then interpreted by the printer driver into instructions to the print engine, which then interprets those into ink on paper.
  In some ways, it’s a miracle that it ever works!
  Howard.
  
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  - 3
    
    Michele Galvagno on February 23, 2019 at 9:31 am
    
    Wow, that’s complicated!
    I guess I will just raise a shrine to the PDF god in my temple!!
    Thanks for explaining this
    
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4

Luisba on February 27, 2019 at 4:36 pm

Hi,

I am using Mojave and I am very frustrated with the way it deals with pdf (I didn’t have that feeling since Yosemite).

As an example, I use a very simple automator service to merge pdf files (just select files from Finder, merge them and save the final file). Well, the problem is that when I merge two files the merged file weight MUCH MORE than the addition of the individual files. As an example, I merged 35 files with a total weight of 450 MB and the resulted merged file was 1,2 GB! I did the same operation with PDF Expert and the resulted merged file is 485 MB. So, the file created with automator is almos 3x the file created with a third party app!!
Other example, although it just happens with some files and not with others (don’t ask me why), is that when I export a pdf applying the reduce size filter in Preview, the resulted file is huge in comparison with the original one (i.e from 3.2 MB to 64 MB!). As I say, with other files it just work fine.

So, PDFs and Mojave is (for me) a terrible experience.

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- 5
  
  hoakley on February 27, 2019 at 5:17 pm
  
  Thanks.
  The underlying PDFKit framework was rewritten for Sierra, and there are still bugs being shaken out of it. I wouldn’t ever use Preview for serious PDF work – it’s a good free PDF reader which has some useful added features, such as converting PostScript to PDF (which isn’t supported by many other apps).
  Whenever you merge PDF files, it’s always worth recompressing them to clean up the result. Again, a third-party tool is by far the best to use.
  Howard.
  
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