MarkupText: Use Cairo to handle gradients

[PhilippImhof]

Enhancement proposal

When using gradients in MarkupText we have Pango render the text to an SVG. We then load the SVG into a SVGMobject and apply the gradient to the characters. This has two major drawbacks:

• the gradient is done on a per-character basis, i.e. every character has one solid color; the quality of the gradient therefore depends largely on the length of the text to which it is applied
• with ligatures, the number of paths does not correspond to the number of characters, so the user will have to specify an offset to compensate for this, e.g. fl counts for two characters but might be rendered as a single glyph
• similar problems arise with underline, double underline, overline and strikethrough, because those lines will also be sub-paths of the SVGMobject

[naveen521kk]

I would like to have this issue in the other repo https://github.com/ManimCommunity/ManimPango, and the issue here should be about SVGMobject supporting them.

[PhilippImhof]

OK fine for me, because in this case (contrary to the other one) we will probably not need to change the markup class. I will take care of it later.

[PhilippImhof]

Closing the issue. It is moved to ManimCommunity/ManimPango#33

[naveen521kk]

you could have used Transfer Issue button :)

[PhilippImhof]

Oh that's neat. Didn't even notice it. They should have made it even smaller :)