Re: Another possible gb.poppler bug?

[gbWilly <gbWilly@xxxxxxxxxxxxxx>]

On Tuesday, December 2nd, 2025 at 02:55, Claus Dietrich <claus.dietrich@xxxxxxxxxx> wrote:

> Am 01.12.25 um 23:07 schrieb gbWilly:
> 
> > Are you sure most pdf files have no thumbnails as most pdfviewers seem
> > to show them for most pdf files, kind of the other way around.
> 
> 
> Yes. Just check what apps have the capability to generate PDF
> thumbnails. This why I needed Windows and Adobe Acrobat to generate a
> test file with embedded thumbnails.

The only pdf files I ever generated are either using LibreOffice or by code in gb.cairo. I guess when using gb.cairo no thumbnails are created inside the pdf.
The LibreOffice documents exported as pdf, do show thumbs in other pdfviewers, I have to self render them in my pdfviewer.

> 
> > I have a 177 page document that opens before I can count to 1 with
> > thumbnails. Self rendering when opening that file means I can count to
> > 3 before it is openen and thumbnails show.
> 
> 
> Why would you render it yourself if embedded thumbnails are there? Just
> use them (and our Gambas apps are doing it).

When my application self renders thumbnails it is because no internal thumbnails are found by gb.poppler. That is my only reason for self rendering, a sort of fall back.
Other pdfviewers seem to give me thumbnails in a second for this file of 177 pages, but gb.poppler doesn't retrieve them and I have to render.

> 
> Am 02.12.25 um 00:16 schrieb Benoît Minisini:
> 
> > The PDF viewer must be modified to be clever, and render the thumbnail
> > only when needed.

It is not about the self rendering, that's a fallback for when no thumbnails are provided.
This topic is about 'are you 100% sure gb.poppler always retrieves the thumbnails from within the pdf file?'


> It doesn't need be modified - it is doing it already. This why I am not
> sure what this is all about.

Yes, that is what I was thinking too, it only renders if no internal thumbs found. It's just the loading speed for files with many pages is annoying when self rendering.
Lower dpi makes it somewhat faster, but it remains slow compared to internal thumbnails and other pdfviewers. I just want to make sure internal thumbs get retrieved 100% of the times when available. That is what this topic is about. Could it be like with the index pages issues something has been overlooked? A yes or no to this question is what I'm looking for.

> In my experience our Gambas apps reliably load embedded thumbnails if
> there are some and the loading is of cause much quicker in that case.
> 
> PDF viewers like XReader or Okular won't provide you with any proof that
> the loaded PDF has embedded thumbnails. If you just look on loading
> times then start with a comparison of XReader and Okular. Sometimes
> there are very huge differences for whatever reason.
> 
> Am 02.12.25 um 01:52 schrieb gbWilly:
> 
> > That exactly what I mean. I have the idea that there are thumbs in several of the files I open, the self render is just a workaround for when nor thumbs are found internal.
> > And just as with the pages, could there something missing (another reference as you say) that prevents from retrieving the thumbs in certain files. That is what I would like to know.
> 
> 
> So far I haven't seen any proof that the PDF files in question have
> embedded thumbnails which gb.poppler doesn't find.

Ok, that's what I'm trying to figure out and if so, then there is no problem.
And you seem to be very convinced that gb.poppler acts correctly. Lee pointed out that certain files didn't have them, but then also had doubts because of the same observations as I have, that other viewers seems to load them in a second what makes you think they are loading internal thumbs from pdf files that 'have no thumbnails internally' according to gb.poppler. How do they do that, or do they do that?

> In my practice I noticed that embedded thumbnails generated by Adobe
> Acrobat don't look as good because of their low resolution. The
> resolution it kept low to increase the loading speed and to keep the
> resulting PDF file size small. The generation of thumbnails is optional
> in Adobe Acrobat and when you generate them with a higher resolution the
> file size is exploding and becomes less suitable for the web or emails.

That seems a very plausible reasoning.

> The thumbnails of the files discussed here rather seem to be self
> rendered by the viewers. So I tend to believe that they don't have
> embedded thumbnails.

Tend to believe or 100% sure? There is a difference.
After reading all (and Lee's findings) this I tend to believe that you might be right, but I'm still not 100% sure.

gbWilly