At 2023-05-10T12:28:02-0500, Dave Kemper wrote: > On 5/10/23, Dave Kemper <saint.s...@gmail.com> wrote: > > Nonintuitively, .ss's units aren't in fractions of standard > > typographical measurements, but 1/12 of the current font's ordinary > > space. > > And I just learned (or maybe relearned) this is a deviation from AT&T > troff's .ss units, which are a fixed 1/36 em.
You might need to unlearn it. $ cat ./EXPERIMENTS/ss.roff .nf A B .ss 12 A B .ss 36 A B (One "cp -l" later...) DWB 3.3 troff does indeed appear to use thirty-sixths. $ DWBHOME=. ./bin/troff ./ss.roff x T post x res 720 1 1 x init V0 p1 x font 1 R x font 2 I x font 3 B x font 4 BI x font 5 CW x font 6 H x font 7 HI x font 8 HB x font 9 S1 x font 10 S s10 f1 H720 V120 cA w97Bn120 0 H720 V240 cA w97Bn120 0 H720 V360 cA wh147cB n120 0 x trailer V7920 x stop One doesn't have to be able to decompile Kernighan's page description language to see that the inter-word space is the same for the first two instances of "A" and "B", and different for the third. (Observe how "97" increased to "147". This is the amount of motion necessary to advance past the "A" itself _plus_ the inter-word space.) What about groff? $ ./build/troff -F build/font -F font ./EXPERIMENTS/ss.roff x T ps x res 72000 1 1 x init p1 x font 5 TR f5 s10000 V12000 H72000 md DFd tA wh2500 tB n12000 0 V24000 H72000 tA wh2500 tB n12000 0 V36000 H72000 tA wh7500 tB n12000 0 x trailer V792000 x stop Here, what's going on is a little more obvious since we're using grout's "t" command instead of Kernighan's optimized syntax for moving and then writing a glyph. "h2500" is used in the first two cases, and "h7500" in the third. It would therefore appear that groff is not deviating from AT&T behavior here, but using 36ths after all, and our documentation is wrong (and has been for a long time). Regards, Branden
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