Review: On the relation of hinting and variations

Posted 30 November, 2016

In a fine article published by Monotype, Part 1: from TrueType GX to Variable Fonts, Tom Rickner – now at Monotype – writes about his first-hand experience at Apple in the team that developed both TrueType and TrueType GX variations. (The latter is of course the basis, practically unchanged, of today’s OpenType Variations that we’re all so excited about.)

Tom brings to life the team’s nervousness back in 1991 when he writes “just 2 months before Apple was able to ship a TrueType enabled System 7, Adobe announced Multiple Masters”. Apple’s determination to be independent of Adobe had resulted in a breakneck race to offer new features dreamed up by typography geeks, each technology trying to position itself as the standard, and the best solution for OS vendors. Two years earlier, Microsoft’s decision to license Apple’s TrueType rather than strike a deal with Adobe, had been a turning point.

Perhaps the most interesting part of the article is how Apple responded technically to Adobe’s Multiple Master fonts. The variations that happen in TrueType GX fonts are closely related to those that happen in TrueType instructions, or hinting. A fundamental aspect of TrueType hinting is to move the default outline points of a glyph based on looking up how stored measurements (for stem widths and other control values) scale according to the number of pixels available. Yet there are also TrueType hinting instructions that move a glyph’s outline points arbitrarily (namely the MSIRP and DELTAP instructions). In other words, a hinted TrueType font is a variable font of remarkable flexibility, yet it is restrained to express its variation only at a particular pixel height, and does not normally expose the adjusted outline.

It’s this latter concept – arbitrary deltas to the default outline points – that is the foundation of TrueType GX variations. Whereas in hinting points jump to new locations based on rasterization conditions, in TrueType GX the degree of movement of a set of points is under the user’s control: you can dial up anything from 0% to 100% for a particular delta set. Both TrueType hinting and variations use the space-saving trick that you only need to move key points, after which any untouched points are moved according to how far their neighbours moved.

Tom Rickner’s article is billed as Part 1, so let’s hope we get more soon from Monotype on the fascinating history of variable font technology.

Tom was also interviewed recently for his local newspaper: Meet Tom Rickner, the Madison type designer who helped pioneer digital fonts as we know them. He talks about his work on TrueType hinting, TrueType GX, the Noto project and taking time away from the computer with letterpress printing.