Hello there !

I'm currently working on manim-web, a js port of this amazing project.
I noticed that the font-size logic was different, so I wanted to investigate to be sure the behavior is the same.

But looking at the source-code of manim, I'm very confused. I think this would be a good opportunity to rewrite, simplify, comment, and rename variables in the code regarding this logic.

I consider contributing, but I have some questions I would like to clarify before.

From what I understand, the pipeline for MathTex is:

1. render the source string to Tex, DPI then SVG. You get an arbitrary size measured empirically (~10 units in the SVG world ?)
2. extract the paths of the SVG, do NOT normalize them
3. call self.font_size = self._font_size which in turns call the setter
4. the setter does self.scale(font_val / self.font_size), where font_size is a getter
5. the font_size getter returns the confusing self.height / self.initial_height / SCALE_FACTOR_PER_FONT_POINT where SCALE_FACTOR_PER_FONT_POINT=1/960.

So that means the output height is SVG_COMPUTED_HEIGHT * (INPUT_FONT_SIZE / (1 / SCALE_FACTOR_PER_FONT_POINT)), which means SCALE_FACTOR_PER_FONT_POINT is a combination of 2 things: "X svg points should be Y pt" and "Y pts should be Z units in manim"

And the pipeline for Text is:

1. compute size = self._font_size and size /= TEXT2SVG_ADJUSTMENT_FACTOR where TEXT2SVG_ADJUSTMENT_FACTOR = 4.8 (

   manim/manim/mobject/text/text_mobject.py

   Lines 801 to 803 in af70b6f

   	size = self._font_size
   	line_spacing = self.line_spacing
   	size /= TEXT2SVG_ADJUSTMENT_FACTOR

   )
2. Use manimpango to extract svg from text with size=size
3. call self.scale(TEXT_MOB_SCALE_FACTOR) where TEXT_MOB_SCALE_FACTOR=0.05

And for one obscure reason the font-size is defined as:

@property
    def font_size(self) -> float:
        return (
            self.height
            / self.initial_height
            / TEXT_MOB_SCALE_FACTOR
            * 2.4
            * self._font_size
            / DEFAULT_FONT_SIZE
        )

with a hardcoded 2.4 value

For this one, I'm still trying to make sense of it.

Questions

• is it true that the svg paths returned by Tex are not normalized ? It's a probably naive question but why ?
• has SCALE_FACTOR_PER_FONT_POINT been set empirically or is there a reason ?
• what does the size argument of manimpango do ? Why is there scaling after svg generation ?
• I suspect the 2.4 has been added just because 2.4 / TEXT_MOB_SCALE_FACTOR is exactly 48, the default font size. Since they cancel out, why not just do self.height / self.initial_height * self._font_size ?
• Wouldn't it be cleaner to have the same logic for Tex and SVG ? Render SVG in SVG point space, and do the same scaling afterward with one single SCALE_FACTOR_PER_SVG_FONT_POINT constant ?

Notes:

• manim/manim/mobject/text/tex_mobject.py

  Line 101 in bbdcda1

  self.font_size = self._font_size

  has both font_size as a setter and _font_size, quite hard to make sense of
• _font_size could be renamed _required_font_size, and assertions could be added so that the person reading the code knows what properties to expect in the code
• SCALE_FACTOR_PER_FONT_POINT should be renamed SCALE_FACTOR_PER_SVG_FONT_POINT at least
• TEXT_MOB_SCALE_FACTOR is defined in this file: https://github.com/ManimCommunity/manim/blob/main/manim/mobject/text/text_mobject.py . If it is really needed, it should go to the constants.py file
• the size argument of manimpango is not documented

I hope my walkthrough is understandable, It was quite an adventure 😅