[NTG-context] how to simulate \hss in luametatex?

[黄复雄]

Dear Max,
I am very grateful that you took the time to tweak and test my
non-running code snippet
and found the problem.

 > local box = node.hpack(hss + b, "exactly", 0)

You are absolutely right, the cause of the problem was that I wasn't
using node.hpack().
Actually, I tried to use it, but used it wrong, as follows:

local box, _ = node_hpack(list)
box.width = 0
box.shift = -tex_sp("1ex")

My app works fine now. Also, I learned a lot from your code, like
font.current(), hss + b
and tex.forcehmode() - I immediately used the last one to set
box.shift, making it relative.

Best regards

Huang Fusyong(黄复雄)

Max Chernoff via ntg-context <ntg-context at ntg.nl> 于2022年11月11日周五 17:55写道：
>
> Hi,
>
> > I want to  simulate \hss  in lua end in ConTeXt/luametatex environment.
> > For example,
> >
> > ```ConTeXt
> > a{\raise 1.5ex\hbox to 0pt{\hss b}}c
> > ```
>
> > And in lua, I do as follows(part of my app seen in attachment):
>
> Your code doesn't compile as is. I think that this is the same thing
> though:
>
>    \starttext
>    \startluacode
>    local a = node.new"glyph"
>    a.char = string.byte("a")
>    a.font = font.current()
>
>    local b = node.new"glyph"
>    b.char = string.byte("b")
>    b.font = font.current()
>
>    local c = node.new"glyph"
>    c.char = string.byte("c")
>    c.font = font.current()
>
>    local hss = node.new("glue")
>    hss.stretch = 65536
>    hss.stretchorder = 2
>    hss.shrink = 65536
>    hss.shrinkorder = 2
>    hss.width = 0
>    b = node.insertbefore(b, b, hss)
>
>    local box = node.new("hlist", "box")
>    box.head = b
>    box.width = 0
>    box.shift = -tex.sp("1ex")
>
>    tex.forcehmode()
>    node.write(a + box + c)
>    \stopluacode
>    \stoptext
>
> > And got 'b' on top of 'c' in pdf as follows:
> >
> > ```pdf
> >   b
> > ac
> > ```
>
> The \hss isn't the problem here. The problem is actually with the box.
> When you manually make the \hbox like that, I think (although I could be
> wrong) that you're bypassing all of TeX's glue calculations. You should
> probably use "node.hpack" instead:
>
>    \starttext
>    \startluacode
>    local a = node.new"glyph"
>    a.char = string.byte("a")
>    a.font = font.current()
>
>    local b = node.new"glyph"
>    b.char = string.byte("b")
>    b.font = font.current()
>
>    local c = node.new"glyph"
>    c.char = string.byte("c")
>    c.font = font.current()
>
>    local hss = node.new("glue")
>    hss.stretch = 65536
>    hss.stretchorder = 2
>    hss.shrink = 65536
>    hss.shrinkorder = 2
>    hss.width = 0
>
>    local box = node.hpack(hss + b, "exactly", 0)
>    box.shift = -tex.sp("1ex")
>
>    tex.forcehmode()
>    a.next = box
>    box.next = c
>    node.write(a)
>    \stopluacode
>    \stoptext
>
> -- Max
>
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