Re: MkIV italic correction?

[Hans Hagen <pragma@wxs.nl>]

Dohyun Kim wrote:

> Considering current state that we don't know any fonts that has ITLC table,
> it would be better than nothing to implement italic correction as follows.
> In the following code, "fontdata" is a table returned by the function
> "fonts.define.read".
> 
>         local param = fontdata.parameters
>         local italicangle = fontdata.shared.otfdata.metadata.italicangle
>         if italicangle and italicangle < 0 then
>             local uwidth = fontdata.shared.otfdata.metadata.uwidth or 40
>             local factor = fontdata.factor or 655.36
>             param.slant = - math.tan(italicangle*math.pi/180) * param.quad
>             for i,v in pairs(fontdata.characters) do
>                 local gl = fontdata.descriptions[i]
>                 local it = (gl.boundingbox[3] - gl.width + uwidth*0.5) * factor
>                 if it > 0 then v.italic = it end
>             end
>         end

there are seleveral solutions:

- extend the font with this info (faster but then it's always there 
which might not be ok as it's an approximation)

- calculate it after loading (which is what you propose)

in the mkiv code we do have a hook for that kind of things so this is 
then what i propose. watch how we don't scale here, we just add an entry 
to the shared data as that's where we hook in; the real implementation 
would look slightly different as an optimization is possible

\starttext

\startluacode
table.insert(fonts.triggers,"itlc")

local function itlc(tfmdata,value)
     if value then
         -- the magic 40 and it formula come from Dohyun Kim
         local fontdata = tfmdata.shared.otfdata or tfmdata.shared.afmdata
         local metadata = fontdata and fontdata.metadata
         if metadata then
             local italicangle = metadata.italicangle
             if italicangle and italicangle ~= 0 then
                 local uwidth = (metadata.uwidth or 40)/2
                 for unicode, d in next, tfmdata.descriptions do
                     local it = d.boundingbox[3] - d.width + uwidth
                     if it ~= 0 then
                         d.italic = it
                     end
                 end
             end
         end
     end
end

fonts.initializers.base.otf.itlc = itlc
fonts.initializers.node.otf.itlc = itlc

fonts.initializers.base.afm.itlc = itlc
fonts.initializers.node.afm.itlc = itlc
\stopluacode

\definedfont[SerifItalic*default at 24pt] test\/test

\definefontfeature[xdefault][default][itlc=yes]

\definedfont[SerifItalic*xdefault at 24pt] test\/test

\stoptext

i could add it to the generic code (although i'm not going to add all 
the other context goodies to the generic code definitely not as long as 
they're experimental)



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                                           Hans Hagen | PRAGMA ADE
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