On fractional coordinates

Theoretically, OpenType PS (.otf) supports fractional coordinates, but there are some technical caveats associated with it. In principle, we could say that the final font formats only support integer coordinates but during the work process, having fractional coordinates would be helpful.

For example, if you have drawn your glyphs on an integer grid, but then you’d like to make some adjustments such as: make it slightly more narrow, then slightly wider, then perhaps slant it by a few degrees and then slant it back, or make some tiny rotations, or maybe scale the glyph down and then up again — on an integer grid, the result will have accumulated the rounding errors from every one of these operations. On a fractional grid, all your shapes (the positions of the BCPs, the angles, the stem thicknesses etc.) will always remain just as in the original design.

Therefore, a hardwired integer grid such as the one in FontLab Studio does impose a certain limitation onto the type designer. A fractional grid such as the one in Fontographer allows you to avoid those rounding errors. But of course, at the very end, when you decide to generate or ship the font, you’ll need to align your points to an integer grid, or the software will do this for you.

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Adam Twardoch

Adam Twardoch is Director of Products at FontLab, and a font consultant specializing in font technology, multilingual typography, CSS webfonts, Unicode and OpenType. He also works as the glyph wrangler at MyFonts. He regularly teaches workshops in font creation and is a board member of Association Typographique Internationale (ATypI). Originally from Poland, he lives and works in Berlin.

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