New checks to ensure all OS/2 metadata is consistent and complete

[davelab6]

@getflourish published the amazing https://medium.com/@getflourish/the-anatomy-of-a-thousand-typefaces-f7b9088eed1 and says, emphasis mine,

While some fonts provide a lot of information, this isn’t always the case, especially not for free or open source fonts such as the ones from Google Fonts. But even if information is provided, it’s not necessarily consistent or complete enough to make comparisons based on it.

We should fix that :)

I took a look at the dictionary data powering his impressive https://getflourish.github.io/anatomy-of-typefaces/app/ and he includes the values of the following OS/2 Table keys:

• [ ] xAvgCharWidth
• [ ] usWidthClass
• [ ] ySubscriptXSize
• [ ] ySubscriptYSize
• [ ] ySubscriptXOffset
• [ ] ySubscriptYOffset
• [ ] ySuperscriptXSize
• [ ] ySuperscriptYSize
• [ ] ySuperscriptXOffset
• [ ] ySuperscriptYOffset
• [ ] yStrikeoutSize
• [ ] yStrikeoutPosition
• [ ] sFamilyClass
• [ ] panose
• [ ] ulCodePageRange1
• [ ] ulCodePageRange2
• [ ] sxHeight
• [ ] sCapHeight
• [ ] usDefaultChar

We should have checks that ensure all of these are consistent and complete across our whole collection.

[madig]

How are you going to check Panose? He doesn't seem to compute that.

[getflourish]

Right, one of my main points about missing information is the lack of Panose. Since most of its values need to be manually calculated and provided by the designer, I don’t think that this is easily possible to add. Technically, all measurements could be done algorithmically though.

[madig]

You could, of course, work out a CAPTCHA thing that makes people classify things, e.g. by showing them comparison images where you know the classification 😁

[felipesanches]

I still need to look more carefully at this one, but this is definitely not worth blocking the v0.5.1 - MFDOS release.

[madig]

One could do a basic PANOSE test that checks if e.g. the weight is classified black but the name table says something else or a serif style has been set when the font name carries "sans" or things like that.