Use ManimPango for Text rendering

[naveen521kk]

Motivation

Pango is a lot better at Text Rendering rather than using a Toy API for Cairo. I had discussed this with @3b1b on Discord.. This will remove the dependency on pycairo.

It also provides another method to add a font file to Pango search path, whose family name can later be called. This method isn't available for macOS yet.

I couldn't find Code here, that would require a small change setting disable_ligatures, or else colours would be broken, due to ligatures.

Proposed changes

• requirements.txt - add manimpango
• text_mobject.py - use manimpango

Test

Running example scenes should work, no breaking API changes. register_font API can be used as

with register_font('roboto.ttf'):
    a=Text("Hello Roboto",font="Roboto")

A list of fonts visible to Pango can be got from

>>> import manimpango
>>> manimpango.list_fonts()
[ ... ]

More API at https://manimpango.manim.community/en/latest/

[3b1b]

Is this the intended behavior?

class TextExample(Scene):
    def construct(self):
        fonts = Text(
            "And you can also set the font according to different words",
            font="Arial",
            t2f={"font": "Consolas", "words": "Consolas"},
            t2c={"font": BLUE, "words": GREEN}
        )
        fonts.set_width(FRAME_WIDTH - 1)
        self.play(Write(fonts))
        self.wait()

[naveen521kk]

Looks like a bug to me. I tried doing the same using Community edition's MarkupText (I didn't bring it here because CONFIG was something out of my understanding), and also the legacy CairoText. I get a video like

from manim import *
class Font(Scene):
    def construct(self):
        fonts = Text(
            "And you can also set the font according to different words",
            font="Arial",
            t2f={"font": "Consolas", "words": "Consolas"},
            t2c={"font": BLUE, "words": GREEN},
            disable_ligatures=True
        )
        fonts_c = CairoText(
            "And you can also set the font according to different words",
            font="Arial",
            t2f={"font": "Consolas", "words": "Consolas"},
            t2c={"font": BLUE, "words": GREEN},
        )
        markup = MarkupText(
            'And you can also set the <color col="BLUE"><span font_desc="Consolas">font</span></color> according to different <color col="GREEN"><span font_desc="Consolas" color="GREEN">words </span></color>',
            disable_ligature = True,
            font="Arial",
        )
        fonts.scale(.8)
        self.play(Write(fonts))
        self.wait()
        self.clear()
        fonts_c.scale(.8)
        self.play(Write(fonts_c))
        self.wait()
        self.clear()
        markup.scale(.6)
        self.play(Write(markup))
        self.wait()

Font.mp4

so it seems like a bug in aligning texts in ManimPango for Text. Can you open an issue in that repo?

[TonyCrane]

Is this the intended behavior?

class TextExample(Scene):
    def construct(self):
        fonts = Text(
            "And you can also set the font according to different words",
            font="Arial",
            t2f={"font": "Consolas", "words": "Consolas"},
            t2c={"font": BLUE, "words": GREEN}
        )
        fonts.set_width(FRAME_WIDTH - 1)
        self.play(Write(fonts))
        self.wait()

But why I don't have this problem?

[naveen521kk]

@TonyCrane I think you don't have the font installed or something like that? Btw which OS are you using?

[TonyCrane]

I think you don't have the font installed or something like that? Btw which OS are you using?

But the result fonts are correct ("font" and "words" are Consolas, the rest are Arial), so I made sure I have installed the fonts.
I am using Windows 10, Python 3.7.3, ManimPango 0.2.2, and the manim source code is the latest.

[naveen521kk]

I think maybe caching issue? Did you run the same example before updating to recent branch which uses pango and the svg file from cairo is cached? That's should be case I think. But still not sure...

[TonyCrane]

Oh, sorry, I just cleaned the cache of Text, and got the same result as you.

But if I kept the disable_ligatures as default True, then the coloring will be incorrect:

---

Fixed in c9e2234.
Because in SVGMobject of ManimCommunity/manim, the empty paths are ignored, but in 3b1b/manim are not. So I added back the remove_empty_path method which you accidentally deleted in this pr.

[naveen521kk]

I don't think that will fix this. The colouring is a bit off because of ligatures where in two letter comes in a single path element of the SVG file. Pango would handle it but the svg parser in both the version isn't that great to handle styles. I have some plans to make it not use SVG instead directly return each character as an ImageMobject or rather return a set of points, but that requires work and isn't yet done. Once that's done this problem will be fixed 😉.

[eulertour]

This PR causes a crash immediately for me and it looks like it's causing other problems from the earlier posts. Can this at least be made optional until it can be done stably?

[naveen521kk]

This PR causes a crash immediately for me

There could be much reason why things crash. ManimPango is necessary for Community Version also. If you say this crashes for you, it should crash for ManimCE also...