I know there are thousands, or maybe millions, of fonts. And every font I have ever seen is made of clean curves. That is, every point on the plane is either 100% black or 100% white.
But when I saw some Calligraphy works, I found that some strokes may be transparent. It looks like the brush was running out of ink but people still consider it to be part of beauty. Here are two examples from Wikimedia:
Also, we can use colors or opacities to illustrate the order of strokes. like this one:
(Oops, the reddest stroke should be the topmost.)
Unfortunately so far I can found only one font showing stroke orders -- in a tedious way.
My question is, are there any fonts contain (partially) transparent glyph? If no, does standers like OpenType support this feature? If still no, is it possible to make one through, say, svg format?
Edit after on hold
Uhh, actually I checked help center and did my best to form this problem. My main purpose is fairly simple (comparing to calligraphy): I want a prove (by showing me an existing font) or a disprove (by pointing out the standard does not support).
Following David Carlisle's comment I found this blog saying:
Our implementation uses a base glyph for reference, which would be used for non-color situations. A data structure, implemented as a new 'COLR' table in OpenType, breaks down the base glyph into a separate set of glyphs, each with its own z-order and single color reference. The color references are handled has palette indices, with a separate table, 'CPAL' in OpenType that resolves the RGBA colors actually used for the glyph.
So that is two features: RGBA and z-index. In addition Microsoft made a new font
Segoe UI Emoji. So that is a prove and I am satisfied with it. I did not want to talk about Chinese Calligraphy. It is just an introduction to opacity issue. (By the way, to be 100% precise, the calligraphy works and the font in link are made by Japanese.)
Probably it will be on-topic if I ask Can I create a colored/transparent font using METAFONT/TikZ? or so. However that would be too bothering. I am leaving this problem here but any comment is still welcomed.