Victor Mote wrote:
Rhett Aultman wrote:

Hm...and what about a fusion of the two.

>>    If the LMs submitted
potential breaks and some sort of information about the
constraint that has to be removed to use them, and this
information was held on to, then at some point down the line in
processing, FOP could rewind back to a past break and select from
the "next best" list...essentially meaning that FOP flies blind
until there's a problem, then goes back and examines a plan of
alternate routes, and after picking one, goes with it and gets
back to work as usual.

Is any of this making sense, or is this all just a bunch of hoohah?

IMHO, not hoohah. That is exactly what I was driving at. The issue, of
course, is that "next best" might be in an entirely different context than
it was before. For example, a line-breaking strategy might have reported
"next best" based on the assumption that it was working in a space 4.5"
wide, but because of an issue with a footnote, a higher-level LM has now
pushed it to the following page where it is next to a graphic that only
leaves it 2.5" to work with. So now the layout needs to be recomputed for
that line entirely.

So now you have to basically keep track of the options that you have tried,
with the scoring opportunities for each one. You basically have to try
options until you find one that scores "acceptably" or until there are no
others to try, at which point, you take the best one that you have.

It seems to me that there are (at least) two approaches: 1. A leaf on the
tree says "I am here, put me somewhere on a page", or 2. A higher-level node
(page-sequence) says "I have some space here, send me something to fill it."
3. 1 + 2.

Thinking that you can do 1. in isolation is, well, brain-dead. On the other hand, how does 2. handle auto table layout? The columns cannot be dimensioned at the very top until the last information about requirements is in from the very bottom. Then the decision is taken at the top, and percolates all the way back down again.

In the much more constrained context of Lout, Jeffrey Kingston describes the back and forward movement of the layout logic in, e.g., Section 2.5 of "The Design and Implementation of the Lout Formatting Language" <>.

Again, I am ignorant (although I have read the related doc), but reading
between the lines makes me think that we are driven to the first option,
which I am betting makes dealing with the higher-level layout issues very
complicated. I'm also surmising that we probably can't do a good job (or at
least can't *know* that we did) until we get the entire page-sequence read
anyway, which means that we might be better off reading it in before we
start & then taking the second approach. FWIW. Actually, I hope to learn a
lot from Keiron's replies.

"Lord, to whom shall we go?"

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