sile 0.14.8

Simon’s Improved Layout Engine
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local pagebuilder = pl.class()
pagebuilder.type = "pagebuilder"
pagebuilder._name = "base"

function pagebuilder:_init ()
  self.awful_bad = 1073741823
  self.inf_bad = 10000
  self.eject_penalty = -self.inf_bad
  self.deplorable = 100000
end

function pagebuilder.collateVboxes (_, vboxlist)
  local output = SILE.nodefactory.vbox()
  output:append(vboxlist)
  return output
end

-- Note: Almost 1/3 of the time in a typical SILE in taken iterating through
-- this function. As a result there are some micro-optimizations here that
-- make it a-typical of preferred coding styles. In particular note that
-- we absolutize heavily iterated lengths as early as possible and make
-- make direct calls to their integer amounts, assumed to be in points by
-- the point they are called **without actually checking**!
function pagebuilder:findBestBreak (options)
  local vboxlist = SU.required(options, "vboxlist", "in findBestBreak")
  local target   = SU.required(options, "target", "in findBestBreak", "length")
  local restart  = options.restart or false
  local force    = options.force or false
  local i = 0
  local totalHeight = SILE.length()
  local bestBreak = nil
  local started = false
  if restart and restart.target == target then
    totalHeight = restart.totalHeight
    i = restart.i
    started = restart.started
  end
  local leastC = self.inf_bad
  SU.debug("pagebuilder", function ()
    return "Page builder for frame " .. SILE.typesetter.frame.id .. " called with " .. #vboxlist .. " nodes, " .. tostring(target)
  end)
  if SU.debugging("vboxes") then
    for j, box in ipairs(vboxlist) do
      SU.debug("vboxes", function ()
        return (j == i and " >" or "  ") .. j .. ": " .. box
      end)
    end
  end
  while not started and i < #vboxlist do
    i = i + 1
    if not vboxlist[i].is_vglue then
      started = true
      i = i - 1
      break
    end
  end
  local pi
  while i < #vboxlist do
    i = i + 1
    local vbox = vboxlist[i]
    SU.debug("pagebuilder", "Dealing with VBox", vbox)
    if vbox.is_vbox then
      totalHeight:___add(vbox.height)
      totalHeight:___add(vbox.depth)
    elseif vbox.is_vglue then
      totalHeight:___add(vbox.height)
    elseif vbox.is_insertion then
      -- TODO: refactor as hook and without side effects!
      target = SILE.insertions.processInsertion(vboxlist, i, totalHeight, target)
      vbox = vboxlist[i]
    end
    local left = target - totalHeight
    SU.debug("pagebuilder", "I have", left, "left")
    -- if left < -20 then SU.error("\nCatastrophic page breaking failure!"); end
    pi = 0
    if vbox.is_penalty then
      pi = vbox.penalty
    end
    if vbox.is_penalty and vbox.penalty < self.inf_bad
      or (vbox.is_vglue and i > 1 and not vboxlist[i-1].discardable) then
      local badness
      SU.debug("pagebuilder", "totalHeight", totalHeight, "with target", target)
      if totalHeight.length.amount < target.length.amount then -- TeX #1039
        -- Account for infinite stretch?
        badness = SU.rateBadness(self.inf_bad, left.length.amount, totalHeight.stretch.amount)
      elseif left.length.amount < totalHeight.shrink.amount then badness = self.awful_bad
      else badness = SU.rateBadness(self.inf_bad, -left.length.amount, totalHeight.shrink.amount)
      end

      local c
      if badness < self.awful_bad then
        if pi <= self.eject_penalty then c = pi
        elseif badness < self.inf_bad then c = badness + pi -- plus insert
        else c = self.deplorable
        end
      else c = badness end
      if c < leastC then
        leastC = c
        bestBreak = i
      else
        restart = { totalHeight = totalHeight, i = i, started = started, target = target}
      end

      SU.debug("pagebuilder", "Badness:", c)
      if c == self.awful_bad or pi <= self.eject_penalty then
        SU.debug("pagebuilder", "outputting")
        local onepage = {}
        if not bestBreak then bestBreak = i end
        for j=1,bestBreak do
          onepage[j] = table.remove(vboxlist,1)
        end
        while(#onepage > 1 and onepage[#onepage].discardable) do onepage[#onepage] = nil end
        return onepage, pi
      end
    end
  end
  SU.debug("pagebuilder", "No page break here")
  if force and bestBreak then
    local onepage = {}
    for j=1,bestBreak do
      onepage[j] = table.remove(vboxlist,1)
    end
    return onepage, pi
  end
  return false, restart
end

return pagebuilder