[BUG-General] Text not working properly on master compared to v0.1.0

[ChristianCoenen]

Describe the bug
I have a method that reads a codefile, creates a Text / Paragraph object and colors it via tokens generated by pygments (through the set_color method on different ranges of the Text object e.g. Text[1:10]).

This is working very neat on version 0.1.0 as the manim image below shows:

However, when I run the same code on the current master branch, I get the following output:

The first problem (resulting in the different style) is that the font is not detected anymore. The fontname is JetBrains Mono Regular and is installed on my PC.

The second problem (resulting in the weird coloring) is that the Text implementation seems to have changed to not include specific characters anymore. This can be seen on the next two images. The first shows v0.1.0 and the second the current version (latest master). It can be seen that the Text object is not of the same length as the raw string that was used to create the Text object.

Would really appreciate if you can provide some clarity about:

1. Whether the Text stripping is intended and why it is done (and what gets stripped)
2. Why the font is not detected anymore

System Specifications

System Details

• OS: Windows 10 v20H2
• RAM: 16 GB
• Python version): 3.8 (venv using Poetry)

Latex details

• Distribution: ManimLaTeX

• Installed packages: default (no new packages installed)

FFMPEG

Output of `ffmpeg -version`:

4.3.1

[naveen521kk]

Yeah, the backend has been changed to Pango and this needs some investigation.

[behackl]

Hello! Thank you for your report.

So, both issues are caused by our recent switch of the text rendering engine from Cairo to Pango; if you want to restore functionality it should be sufficient to change Text(lines_str, **config) over here

manim/manim/mobject/svg/text_mobject.py

Line 393 in a0548a7

self.lines_text = Text(lines_str, **config)

to CairoText(lines_str, **config).

We also know that the characters that are being stripped from the text are the spaces; the coloring is applied to the code as if the spaces were still counted (which is why it looks so off).

I have no idea about why the font is not detected, however -- @naveen521kk, do you know?

[naveen521kk]

Maybe the family name be wrong?
I have no idea about it. Did you get any console warning saying that you may get ugly text? (If you are running on pycharm terminal please try and switch to cmd to see it).
Also, if it doesn't make any error message we can't figure it out we can't do anything because we dont have access to the C API underneath it.
Also, is it possible to add a link to the font so that we can try it?

[leotrs]

I can confirm that in the past I've tried selecting a font that I know is installed in my system, but Pango will just use the default font without any kind of visible error message.

[naveen521kk]

Pango uses Fontconfig at the backend to select font(we literally has no access to its API). Maybe your font config is not configured properly to detect it?
@leotrs try running fc-list and check your font is there? If it is pass the exact family name and try again.

[huguesdevimeux]

See #625

[leotrs]

@naveen521kk good recommendation. We should document somewhere that PangoText can only access fonts that are shown when you run fc-list.

[naveen521kk]

The thing is windows users will not have fc-list because windows doesn't use Fontconfig to manage it's font. It uses its own font API.

[ChristianCoenen]

Thanks for the quick responses. Using CairoText works for me. But I think I'll update my code then to colorize the PangoText correctly (I read that Cairo might be dropped in the future). I also didn't know about Code mobject. Will take a look at it.

Good to know about the font. JetBrains Mono is not listed when running fc-list.

@naveen521kk I was able to run fc-list on Windows

[naveen521kk]

(that could be because you have installed full gtk.)

[ChristianCoenen]

Its a fresh Windows installation with only PyCharm, Python, Poetry, GitKraken, manim dependencies, DaVinciResolve and Discord. There is nothing named gtk on it (not even a folder). But yeah, its probably due to some other dependency that made the command available (probably ManimLatex?).

Anyway, so the problem is that fonts which are not listed by fc-list are not found by Pango. So, is there any way to install the font on Windows in a specific way that it is listed? I haven't found anything about it.

[naveen521kk]

Even I don't know. Usually installing the font will simply work out of the box.
Also, you may have installed one of manim dependency which contains that, especially if you would have followed tob, tutorials.

[naveen521kk]

Found out on discussing with Pango developers that this is because of ligatures and can't be avoided. But Pango itself can handle colours but currently, our SVG parser doesn't support this. So, moving the Text class to not use the SVG parser may be one way but that requires a lot of work and the binding we use isn't complete. So, one now using CairoText would be a possible solution and also making the CodeMobject use CairoText.
leifgehrmann/pangocairocffi#19
https://gitlab.gnome.org/GNOME/pango/-/issues/516