Re: bugs in the font metrics for symbol fonts

[Greg A. Woods]

[ On Wednesday, October 16, 2002 at 10:08:47 (+1100), Jeff Kingston wrote: ]
> Subject: Re: bugs in the font metrics for symbol fonts
>
> A fun way to investigate these kinds of things is to
> print the suspect characters in a very large font,
> enclosed in a @Box with margin { 0i }.  The box
> will exactly reflect the font metrics, and so
> you can see clearly whether they agree with the
> actual print area.

Well, that's absolutely fascinating indeed!  Thanks very much for this
most important and revealing clue!

It would seem the arrowhorizex extends to the left of its font metrics
boundary by some tiny amount.

Further it seems the boxes around the arrows are both otfset a tiny bit
to the left instead of being offset in the direction of the point!

The combination of these two errors causes a very visible gap for the
right-pointing arrow when it follows an arrowhorizex "line"!

@SysInclude { langdefs }
@SysInclude { bsf }
@SysInclude { dsf }
@SysInclude { docf }
@Use { @BasicSetup }
@Use { @DocumentSetup }
@Use { @OrdinarySetup }
@SysDatabase @FontDef  { fontdefs }
@Document
//
@Text @Begin
example arrows with horiozontal extenders showing gap on top one
@CD 2i @Font { @Sym arrowhorizex | @Sym arrowright // @Sym arrowleft | @Sym 
arrowhorizex }
@PP
box wraps the line very tightly! "  "
@CD @Box margin { 0.0i } { 2i @Font { @Sym arrowhorizex } }
@PP
box is set away from the line with a margin and is now obviously off to the 
right a bit
@CD @Box margin { 0.5f } { 2i @Font { @Sym arrowhorizex } }
@PP
box is to left of arrow as expected
@CD @Box margin { 0.0i } { 2i @Font { @Sym arrowleft } }
@PP
box is also to left of this arrow too!
@CD @Box margin { 0.0i } { 2i @Font { @Sym arrowright } }
@End @Text


> I'm not sure that I would be keen to actually change
> the font metrics file.  It came from Adobe.

Hmmm.... yes, I understand.  I bet it is buggy just the same!  ;-)

(I seem to remember Chris Lewis muttering over bugs in AFM files back
when he was working on psroff too.  I don't know if he wrote the program
to do it or not, but I remember helping him look over font tables that
we printed out with a little PostScript program)

>  A better
> bet would be to package up the combinations you need,
> using overstriking to correct for the problems.  If
> you use something like
> 
>     @OneCol { @Sym arrowleft |0.456fo @Sym arrowright }
> 
> you can make something that works at any scale.
> 
> Hope this helps.

Yes, that whould work well enough and be more or less portable across
buggy and fixed AFM files too I guess.  Thank you!

-- 
                                                                Greg A. Woods

+1 416 218-0098;            <address@hidden>;           <address@hidden>
Planix, Inc. <address@hidden>; VE3TCP; Secrets of the Weird <address@hidden>