使用 luatex 通过 epdf 库解析链接

Question

要访问页面上的所有链接，您可以使用，getAnnotsObject因为每个链接都是一个注释。未记录的与getAnnotsObject已记录的类似getAnnots，只是它确实存在。注意：这是一个<Object>包含数组，而不是Annots类型的。

然后，您必须手动解析 Annots 以确定哪些注释是链接：只需查看SubtypeAnnotation 目录的字段。如果您找到带有子类型的注释字典Link，则可以尝试确定目的地。根据 PDF 规范，这要么在中Dest，要么在中的动作字典中A。A也可以包含其他类型的操作，但我们忽略这些。此外，一些目的地可能会直接指定而没有名称，这些目的地不能轻易地包装在对象中LinkDest：

local function parse_links (pdf)
  local doc = epdf.open(pdf)
  local cat = doc:getCatalog()

  for page_num=1,doc:getNumPages() do
    print("Analysing page " .. page_num .. ".")
    local page = cat:getPage(page_num)
    local annots = page:getAnnotsObject():getArray()
    if annots then
      for i = 1,annots:getLength() do
        local annot = annots:get(i)
        annot = annot and annot:getDict()
        if annot and annot:lookup"Subtype":getName() == "Link" then
          local dest = annot:lookup"Dest"
          if dest:isNull() then
            local a = annot:lookup"A":getDict()
            if a and a:lookup"S":getName() == "GoTo" then
              dest = a:lookup"D"
            end
          end
          if dest:isString() or dest:isName() then
            dest = cat:findDest(dest:getString() or dest:getName())
          else
            -- In this case we get a direct reference to the destination array
            -- This is *NOT* a LinkDest object, but all the information could be extracted manually
            -- This case will not appear with LaTeX/hyperref documents AFAICT, so we ignore it
          end
          local rect = annot:lookup"Rect":getArray()
          -- Let's print the position on the page and the destination object
          print(rect:get(1):getNum(), rect:get(2):getNum(), rect:get(3):getNum(), rect:get(4):getNum(), dest)
        end
      end
    end
  end
end

正如您所见，该epdf库非常冗长，感觉好像缺少了一半的实现。此外，有些东西甚至可能无法实现：例如，您可以Dests通过访问列表:getDests，但现代 PDF 文档将其目的地包含在名称树中，而不是在 Dests 中。似乎没有任何方法可以直接访问名称树。

对于当前版本的 LuaTeX，epdf已被取代pdfe。该库在较低级别上工作：它对注释、链接或名称树一无所知，而是提供对原始 PDF 对象的访问，您必须自己解释它们。例如，可以使用pdfe列出所有链接及其目的地pdfe

local function lookup_name(tree, name)
  -- A PDF name tree is a tree of multiple arrays with name object pairs,
  -- where each node documents the names it is responsible for using /Limits
  -- For details, read the PDF specification
  local sub = tree.Limits
  if sub then
    if name < sub[1] or name > sub[2] then
      return
    end
  end
  sub = tree.Names
  if sub then
    for i = 1,#sub,2 do
      if sub[i] == name then return sub[i+1] end
    end
    return false
  end
  sub = tree.Kids
  for i = 1,#sub do
    local r = lookup_name(sub[i], name)
    if r ~= nil then
      return r
    end
  end
  return false
end
local dest_to_string_workers = { -- How to print the destination, you could add e.g. FitH
  XYZ = function(p, d)
    return ("page %i at position (%f,%f), zoom factor %s"):format(p, d[3], d[4], d[5] or "none")
  end,
}
local function dest_to_string(d, dest)
  if dest.D then dest = dest.D end
  local page_no
  for i = 1,#d.Pages do
    if tostring(d.Pages[i]) == tostring(dest[1]) then
      page_no = i
      break
    end
  end
  return (dest_to_string_workers[dest[2]] or function()return""end)(page_no, dest)
end
function show_links(filename)
  local d = pdfe.open(filename)
  if not d then error(([[Unable to open "%s".]]):format(filename)) end
  for i=1,#d.Pages do
    local annots = d.Pages[i].Annots
    if annots then -- We have annotations on this page
      for j = 1,#annots do
        local annot = annots[j]
        if annot.Subtype == "Link" then -- We found a link
          local dest = annot.Dest or (annot.A and annot.A.S == "GoTo" and annot.A.D)
          if dest then
            if type(dest) == 'string' then
              local dest_name = dest
              dest = lookup_name(d.Catalog.Names.Dests, dest)
              print("On page " .. i .. " at position (" .. annot.Rect[1] .. "," .. annot.Rect[2] .. ") we found a link with destination \"" .. dest_name .. "\" on " .. dest_to_string(d, dest))
            else
              print("On page " .. i .. " at position (" .. annot.Rect[1] .. "," .. annot.Rect[2] .. ") we found a link with destination on " .. dest_to_string(d, dest))
            end
          else
            print[[This destination is not supported...]]
          end
        end
      end
    end
  end
end

pdfe还允许迭代名称树以列出所有目标树：

local function show_name_list(tree)
  local sub = tree.Names
  if sub then
    for i = 1,#sub,2 do
      print(sub[i])
    end
    return
  end
  sub = tree.Kids
  for i = 1,#sub do
    show_name_list(sub[i])
  end
end

function show_dests(filename)
  local d = pdfe.open(filename)
  if not d then error(([[Unable to open "%s".]]):format(filename)) end
  show_name_list(d.Catalog.Names.Dests)
end

Answer 1