Regular fonts with italic angle marked as italic

[kjarosh]

The following code makes regular fonts to sometimes be considered as italic.

ttf-parser/src/lib.rs

Lines 1451 to 1456 in 7b58ee3

	/// Checks that face is marked as *Italic*.
	#[inline]
	pub fn is_italic(&self) -> bool {
	// A face can have a Normal style and a non-zero italic angle, which also makes it italic.
	self.style() == Style::Italic || self.italic_angle() != 0.0
	}

I'm not sure if that's correct, as I've stumbled upon a font that's regular, but has italic angle set. It's considered as a regular font on my system (and it looks regular, no slant), so it looks like relying on italic angle is not the right approach here.

There's also the question whether oblique fonts are also classified as italic, as in some (usually application-level) contexts they are.

So I guess it depends on what's the definition of "is_italic". The doc doesn't help much in this regard, so I think there's a room for improvement here.

[RazrFalcon]

The problem with fonts in general is that there are no rules about how to parse them. There are no such thing as a correct/reference parser. Every library/OS does whatever it wants.
ttf-parser tries its best, but if you want more control, you have to access individual table fields yourself.

Also, I cannot find the issue right now, but someone asked for this specific change (aka the italic_angle check), because their fonts were misdetecting.
So both options are correct and wrong at the same time.

[LaurenzV]

I think that was me, but I also don't remember anymore where.