From 18387fe2615f814b1f08627a8a06a97449fe1a0f Mon Sep 17 00:00:00 2001 From: Joe Neeman Date: Sun, 20 Feb 2011 10:08:08 +1100 Subject: [PATCH] Add documentation on how to use Page_breaking. --- lily/page-breaking.cc | 54 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/lily/page-breaking.cc b/lily/page-breaking.cc index d5f71297b8..4e386b8183 100644 --- a/lily/page-breaking.cc +++ b/lily/page-breaking.cc @@ -71,6 +71,60 @@ discarded after a call to set_current_breakpoints, since that Line_division refers to a subset of chunks which might be different from the current subset of chunks under consideration. + + HOW TO WRITE A PAGE BREAKING ALGORITHM + All page breakers supported by this class work more-or-less in the same way. + First, they request a particular number of systems by saying + set_current_breakpoints (0, last_break_position (), system_count) + (never mind what the first two arguments do, I'll get to them later). + Alternatively, you can do + set_to_ideal_line_configuration (0, last_break_position ()), + and the number of systems will be automatically chosen according to what + the line breaker wants. + + If there are multiple scores, there will be many different ways to achieve + a certain number of lines. You can see how many alternatives are available + with current_configuration_count (). For every i from 0 to + current_configuration_count ()-1, you can see the line division of the + corresponding configuration with current_configuration (i), or you can try + out various page configurations with one of the space_systems_xxx or + pack_systems_xxx functions. The first argument to each of these functions + is the configuration index. + + When you're done trying out configurations and you've picked the one + you want, do + break_into_pieces (0, last_break_position (), line_division_that_you_want); + return make_pages (systems_per_page, systems ()); + where systems_per_page is a vector of numbers telling how many systems are + on each page. You can get your systems_per_page vector by looking inside + the Page_spacing_results that are returned by space_systems_xxx or + pack_systems_xxx. + + A note on performance: set_current_breakpoints is EXPONENTIALLY SLOW unless + you constrain it by giving it a lower or an upper bound on the configurations + it looks for. Optimal_page_breaking, for example, works by trying + out a bunch of configurations, increasing the system count by one, trying + again and so on. Each time we increase the system count, we assume that the + best new configurations are going to be elementwise larger than the + best configuration for the previous system count (in other words, we're going + to get a new configuration just by adding an extra line to sone score + and leaving the rest the same). Therefore, we pass the best previous line + division as an lower bound to set_current_breakpoints. + + Now you should be in a position to understand Optimal_page_breaking::solve. + Go ahead and read that before finding out, in the next paragraph, + what the first two arguments to set_current_breakpoints do. + + "BREAKS" + Sometimes, it's useful to run this whole page-breaking machinery on a subset + of the book. To do this, you can mark certain "breaks" in the book (a poor + choice of name, perhaps, since a "break" here is different from a page break) + and you can run page breaking between any two breaks. You mark your breaks + by providing a Break_predicate (and, if you want, a Prob_break_predicate) + to Page_breaking's constructor. You then choose a subset of your book + by passing the starting and ending breaks to set_current_breakpoints. You + can see an example of this in Page_turn_page_breaking, where there is a break + everywhere that a page turn is allowed. */ #include "page-breaking.hh" -- 2.39.2