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Jacob Casal
Posts: **98**

Among other things, I started to look into the data that goes into making an italic. In trying to find out what the aforementioned values in hhea meant I came across Apple’s manual noting:

Note that since the slope is a *ratio*, values may be used which simplify or speed up calculations. A

`caretSlopeRise`

of 8 and `caretSlopeRun`

of 6 means the same thing as `caretSlopeRise`

of 4 and `caretSlopeRun`

of 3.I also found Adam Twardoch’s comment about “rational angles,” which used simplified values.

However, as I looked into some italics from fonts I have (Harriet Text, Quadraat, Akko, and others) each had a caretSlopeRise of 1000 units and varied in the caretSlopeRun. Some could not be simplified, but others certainly could be. I figured it had something to do with the bounding box, but that doesn’t make sense considering a vertical font’s values would be the simplified Rise 1, Run 0.

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## Comments

1,70366On my fonts, I (for some reason) decided to keep the numbers small and have an 8-way case statement that uses different scales based on ranges of tan(90-italicAngle). The ranges are set so that the results is within half a degree for all

integervalues of italicAngle (I keep my italicAngle integers).I am guessing that the only practical use for the caretSlopeRise/Run values are when drawing the shape of a selection range ...

If so, I am thinking that finicky precision in setting these is not really needed ... plus or minus half a degree should be OK, yes??is that correct?981,703981,902Maybe it has some other use, but yes, within half a degree should be more than enough accuracy for this purpose.