Re: Diacritical tilde (~) above a letter in eqn

[G. Branden Robinson]

Hi Damian,

At 2023-06-19T20:44:24+1000, Damian McGuckin wrote:
> It has been observed that both $x tilde$ and
> 
>       .EQ
>       x tilde
>       .EN
> 
> has the tilde slightly too far to the right above the italic 'x'.
> 
> On the other hand,
> 
>       .EQ
>       roman { x tilde }
>       .EN
> 
> has the tilde in the correct spot.
> 
> I noticed that $x utilde$ has a similar problem.
> 
> The other diacritical marks, dot, dotdot, hat, vec, dyad, bar and
> under do not have this problem - they are centered very nicely,

It _sounds_ like the tilde and utilde are not, for some reason, honoring
the base glyph's "skew", a measurement explained only in the context of
the fancy GNU eqn "special" primitive.

    special troff-macro e
        Construct an object by calling troff-macro on e.  The troff
        string 0s contains the eqn output for e, and the registers 0w,
        0h, 0d, 0skern, and 0skew the width, height, depth, subscript
        kern, and skew of e, respectively.  (The subscript kern of an
        object indicates how much a subscript on that object should be
        "tucked in", or placed to the left relative to a non-subscripted
        glyph of the same size.  The skew of an object is how far to the
        right of the center of the object an accent over it should be
        placed.)  The macro must modify 0s so that it outputs the
        desired result, returns the drawing position to the text
        baseline at the beginning of e, and updates the foregoing
        registers to correspond to the new dimensions of the result.

I can't promise to dig into this right away, but that is where I'd
start.

Regards,
Branden

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