Hi all

I am still thinking about justification and the more general problem of
line-breaking, and I have come to think that it's quite "strange" that the
LineLayoutManager should make choices about breaking points using only the
information provided by the TextLayoutManagers, while it should have a
wider knowledge of all the text.
(I see bug 28706 as an example of this strangeness: the LLM wants the TLM
to say if there is other text after the returned BreakPoss, but the TLM
doesn't know of the other TLMs' text)

At the moment, lines are built one at a time, and in "normal" cases only
underfull lines are taken into account: as both bpDim and availIPD have
.min == .opt == .max, no BreakPoss is added to vecPossEnd and the chosen
one is simply the last "short" BP returned by a TLM.
Even if bpDim had .min != .max, the choice would be made between a few
alternatives for the current line, without considering what will happen
next; this could generate an output alternating tight and loose lines,
which is not very beautiful.

So, I have tried to implement Knuth's line-breaking algorithm [1], which
calculates breaking points after having gathered information about a whole
Here are a few advantages of this algorithm:
- first of all, the output is very beautiful; there is not a big
  difference in width between spaces in consecutive lines, and the max
  space width is smaller than before
- the interaction between LLM and TLM is quite the same; the TLM returns a
  different kind of objects, much smaller
- the TLM code is simplified a bit, as it has no more to handle leading
  spaces, or calculate flags (which IMO are rather line-related than
- the LLM now can quite easily handle properties such as text-indent,
  text-align-last, word-spacing and letter-spacing

Could I open a bugzilla issue and attach a patch? It would be quite a raw
patch, as I took some short cuts to make it work and there could be some
useless variables, anyway it works and could be used to show the quality
of the output. I have tested it with text-only blocks, so I don't know
what could happen in more complex situations.


[1] D. E. Knuth and M. F. Plass, "Breaking paragraphs into lines"; I found
this essay in D. E. Knuth, "Digital typography", published by CSLI

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