[Software] Fonts are not displayed correctly on a certain website and it only seems to happen on my Debian installation

[Borg]

In an online bookstore, the mathematical symbols are not displayed correctly in a certain font when displaying the reading sample of a certain book. Instead of an equal sign, for example, the Unicode character 𝕴 U+1D574 is displayed. And that's just one character out of many that is not displayed correctly. The error occurs on both Firefox and Chromium.
At first I thought it might be the website, but that doesn't seem to be the case. Because when I view the sample of the book in a VM on a Debian Live CD, in Linux Mint Debian Edition, Ubuntu 24.04 Beta or Windows 10, the mathematical symbols are all displayed correctly. The problem only seems to occur on my Debian installation. Which is Debian 12.5 (stable). The initial installation was with Debian 10 stable and was then upgraded to Debian 11 and later to Debian 12.

Code: Select all

$ inxi -S
System:
  Host: ########### Kernel: 6.1.0-20-amd64 arch: x86_64 bits: 64
    Desktop: KDE Plasma v: 5.27.5 Distro: Debian GNU/Linux 12 (bookworm)

I only use packages from the official Debian package repository. And apart from the Intel microcode and the NVIDIA drivers, nothing proprietary is installed.
Now I would like to know why that is. While a fresh Debian Live CD hardly installed anything, I of course installed a lot of other packages from the Debian repository. What's also strange is that the affected font could be a font embedded in the document. In this case, I'm surprised that the formulas are displayed correctly in a fresh Debian installation. Because if the font is embedded in the data, then it should also be displayed incorrectly in the Debian Live CD, but that is not the case.

Steps to reproduce (if you are affected):
1. Open the following link, it is showing the page of the book "Real-time Rendering" ISBN 978-1-138-62700-0
https://www.thalia.de/shop/home/artikel ... 1049479583

2. Make sure that JavaScript is enabled in your browser, then click below the book's front cover picture on the word "Leseprobe" (in English this can be translated to "Read sample").

3. This will open the reading sample of the book. The book itself is in English.

4. Now go to chapter "1.2.1 Mathematical Notation" and look at the representation of a vector.
On my system I see the following on Firefox and Chromium:

      vx
v 𝕴 vy⇔
    vz

But the following should be shown:

      vx
v = vy,
    vz

Yes, bracketing is missing for the vector in the document, but this is missing not only on my system, but also in the VM with the guest systems of a Debian Live CD, Windows 10 and the other systems mentioned above where the other characters are displayed correctly. The brackets are displayed in the reading sample on Amazon. The same applies to the square bracket for displaying the matrix.

Since this is just one example of many, it gets even worse a few pages later in the book. Instead of mathematical symbols, completely different symbols are displayed. In the matrix display under formula (1.1), the infinity symbol is displayed instead of subscript digits for numbering for each entry.

The font in use can be changed in this reading sample view by pressing on the font button labeled with AA in the upper right corner and there you can change the selected font in the key value pair labeled with "Schriftart". If i change the selected fonts from "Verlagsschrift" to something else, for example "Ubuntu" then everything is shown correctly.

[Linuxgaming1824]

That's a really interesting problem you've identified!

...on a Debian Live CD, in Linux Mint Debian Edition, Ubuntu 24.04 Beta or Windows 10, the mathematical symbols are all displayed correctly. The problem only seems to occur on my Debian installation. Which is Debian 12.5

Hmm that suggests, that between the debian live CD, and it's installation, and then updates to the browsers, the problem has been introduced!

If you want to just get it fixed, there are actually official debian repositories for web browsers hosted by the organizations that make them, such as firefox! They have their own repository where you can get the latest updates for their product, with instructions you can find on their website here...

Using Debian, Ubuntu or any Debian-based distribution?
You can set up our APT repository instead.

Mozilla debian repository installation instructions

a font embedded in the document.

if the font is embedded in a document that would suggest that the document viewer doesn't reference external fonts to render it! So, external fonts shouldn't effect it's appearance in that case.

It sounds like you've identified a problem with the fonts themselves, and the specific versions relative to the browsers you have tested.

You're reading a pdf in a web viewer? Or rather it's a book, that has been formatted to be viewed on the web it sounds like, and the system for rendering it's fonts, as opposed to displaying embedded fonts, such as with a pdf file, is behaving inappropriately with debian 12.5

[Borg]

That's a really interesting problem you've identified!

I agree it is really strange.

Hmm that suggests, that between the debian live CD, and it's installation, and then updates to the browsers, the problem has been introduced!

The Debian 12 LiveCD in the VM is newer than the Debian 10 LiveCD that I used to install back then.

a font embedded in the document.

if the font is embedded in a document that would suggest that the document viewer doesn't reference external fonts to render it! So, external fonts shouldn't effect it's appearance in that case.

That's what the font name suggests, so that's an assumption on my part. It's called "Verlagsschrift", in English this could be translated as "Publisher's Font".

It sounds like you've identified a problem with the fonts themselves, and the specific versions relative to the browsers you have tested.

If one assumes that an installation starting with Debian 10 is updated and all relevant fonts and programs are cleanly overwritten with the newer packages from Debian 11 and 12, then the only place where legacy issues could still be found would be in the user-specific ~/.mozilla/ directory.

On the other hand, the error also occurs for me under Chromium and Chromium doesn't actually use the ~/.mozilla directory. Which is why it must be an error that must be somewhere else in /usr in some files, for example in the font packages. Or if it's the user folder, then perhaps in some kind of font cache, which is used by both Firefox and Chromium.

If it is no such thing, the most likely explanation would be that some program or font package that is not installed in the LiveCD, meaning you have to install it manually later via apt, overwrites the corresponding font data.
That would be a plausible explanation and then there must be other users who have also installed this program or font package and therefore have the same error. However, the likelihood that they will encounter such a problem in their daily work with their system as i did is very small.
And the effort involved in finding this possible package by installing and comparing it, should it be so, is great.
For example, I have installed a few TeX software and a few various font packages on my system, all from the Debian package repository. They are definitely not installed in the LiveCD yet.
However, if necessary, I could post a list of all installed packages from the Debian repository.

You're reading a pdf in a web viewer? Or rather it's a book, that has been formatted to be viewed on the web it sounds like, and the system for rendering it's fonts, as opposed to displaying embedded fonts, such as with a pdf file, is behaving inappropriately with debian 12.5

It's definitely not a pdf. I suspect some sort of epub format embedded into the website. If you click on the "Reading sample" label ("Leseprobe" in German) on the book's shop page above, a kind of webreader, probably JS software will be executed in the Browser, which for a brief moment introduces itself as "Tolino".

A search for “Tolino” resulted in the following manufacturer website:
https://mytolino.com/tolino-webreader/

EDIT:
Btw. only the reading sample on Amazon seems to be an embedded pdf.

[Linuxgaming1824]

You've identified the fonts responsible for the error you've discovered?

Didn't you say you changed the fonts, and the problem was fixed.

[Borg]

You've identified the fonts responsible for the error you've discovered?

Didn't you say you changed the fonts, and the problem was fixed.

I said the following:

The font in use can be changed in this reading sample view by pressing on the font button labeled with AA in the upper right corner and there you can change the selected font in the key value pair labeled with "Schriftart". If i change the selected fonts from "Verlagsschrift" to something else, for example "Ubuntu" then everything is shown correctly.

The error only appears with the "Verlagsschrift" font only. It doesn't appear with other fonts.
If we assume that the font is embedded, then I don't know why it is displayed correctly in the VM on the Debian Live CD, for example but not on my system with different browser. Because if the font itself were faulty, then it would have to have the fault everywhere.
That's why I find this all very strange.

[Linuxgaming1824]

What you are describing, is specifically the font. The rendering system for the book you are observing isn't going to completely change the entire symbol, into an entirely different symbol, it needs the fonts to determine what goes where. The thing is, "everywhere" does not describe the same system. Each system is different. Even the same fonts, the same package for example, taken to a different system, are now those same fonts, but in a different system. These distinctions are critical for narrowing down exactly what is wrong.

How are fonts rendered? That's what I'm wondering now reading the problem as you're describing it. How does a program decide which fonts go where? Your problem might be summarily described as a "bug" by others, because it annoys you, but is fixed with alternate versions of the software. I think it's interesting to think about and examine too.

[Borg]

What you are describing, is specifically the font. The rendering system for the book you are observing isn't going to completely change the entire symbol, into an entirely different symbol, it needs the fonts to determine what goes where. The thing is, "everywhere" does not describe the same system. Each system is different. Even the same fonts, the same package for example, taken to a different system, are now those same fonts, but in a different system. These distinctions are critical for narrowing down exactly what is wrong.

I agree. But the thing is, this JS script stuff should behave everywhere the same. Especially if the fonts are embedded and the browser is the same.

How are fonts rendered? That's what I'm wondering now reading the problem as you're describing it. How does a program decide which fonts go where? Your problem might be summarily described as a "bug" by others, because it annoys you, but is fixed with alternate versions of the software. I think it's interesting to think about and examine too.

Now I'm wondering if the NVidia drivers could mess up the font selection and then render the wrong font. Unlikely, but I don't want to rule it out either.
It would at least be an explanation to the effect that the error does not occur in the VM of the Live CD. Because in the VM no NVidia drivers are used. But then I probably wouldn't be the only one with this problem. Anyone who has an NVidia GeForce GTX 1070 with drivers 525.147.05 from the Debian repo should then be affected by this bug.

[reformedhatter]

I had a similar issue with Firefox and fixed it by going to Firefox, Settings, General, Fonts and click the Advanced box. At the bottom of the window untick where it says Allow pages to choose their own fonts... Restart Firefox. Not sure if it will help you, but it might.