Style of math operators distinctively changed after PR #272

[kauesena]

The opening of this issue comes from a brief discussion in the comments of the pull request #272 adressing the issues #63, #164, and #227. The PR changed the style of many of the glyphs besides fixing the size and alignment problems.
This file from the PR post compares the glyphs side by side.

The style of some characters is distinctively changed. For example, the symbol ± is now connected and the aperture of characters such as ≤, ⊂ is wider.

[ivo-s]

Hey guys, I'm just popping by to let you know not to put too much weight on the status quo. It's because I'm not a typographer. My goal was to make the mathematical symbols bigger and more consistently aligned to make them suitable for display math typesetting. I tried my best to make them click with the text font, but I'm not a professional. I was sort of averaging the dimensions and principles I saw in Computer Modern and STIX fonts. But still, how "big and open" the glyphs ended up was a subjective choice. The joined ± glyph is specifically inspired by CM. Sorry if I made things too complicated.

[kauesena]

I could feel CM was an inspiration for the new glyphs... :) The old ones were indeed kind of unsuited for display style, but the current ones are not very much in harmony with the whole style of the font. I suppose some of us come to Libertinus trying to get away from CM and some come still fond of some of CM's features. I'm afraid I'm more in the first group. But I am not a typographer either and I am quite oriented by preference too.

[ivo-s]

Hey @kauesena, see #454 for dicussion about changing and non-changing of some operators.

[kauesena]

Hi. I've started work on the design of a another set of math operators matching more closely the original design of them. I've being using directly fontforge to do that (should I be doing that? it seemed the easiest way) and using Libertinus 6.6 as reference. Are there things you'd like to comment? @ivo-s @alerque

[kauesena]

I think increasing the union and intersection symbols would be good. The binary ones, I mean.

[kauesena]

[ivo-s]

Please bear in mind that #454 is still not resolved and that many glyphs there are different from the current master branch.

I have also spent considerable time looking for guiding principles in other mathematical fonts, such as the optical size, prominence of operators and math readability, baseline and math axis alignment, line thickness and white gaps ratio, and symmetries in size and position. Some principles concerning the inequality and set operators are discussed in #454. For example, I only found one physics textbook where the operators are (sometimes) closer to the size of your new +. In my experience, dedicated math fonts always feature bigger operators and I found that it is quite important for readability. Same goes for the angle and white space in <, >, and ⊂. I spent quite some time fiddling with the size of basic operators like + or = until I was sure that it works well with the stroke thickness and the average stroke thickness of the text font. For that, one needs to see how the same stuff works in hairline math fonts like CM as well as stocky fonts like Stix2Math. In the above samples, I see the operators getting smaller and more vertically compact, the vertical alignment is different, and the width and line thickness differs between similar types of operators.

All I'm trying to say that not all the changes made were arbitrary style decisions. As I spent a lot of time harmonizing and tweaking a lot of glyphs, and you would need to do the same, I'd like to establish some common ground.

I think the stroke terminals are definitely up for discussion. I just preferred the simplicity over asymmetry so I wouldn't have to differentiate between = and > and then deal with different strokes in one glyph like ≥. Perhaps also stuff like terminating some non-horizontal and non-vertical lines (<,>) perpendicularly, although with this stroke thickness, that would probably sit better with a sans-serif geometrical font. Brackets styling, arrowhead styling, curve shapes, wiggly shapes, the tilde, the amount of space to achieve good grayness, perhaps optically adjusting strokes in corners and intersections...

On the other hand, what I think should follow some general principles are the size and common elements among related glyphs (dimensions, symmetries and common strokes like in ⊂and ∈). That means I would definitely like to retain bigger operators, taller inequalities and set operators, and the optical width of ~530.