cpdf-source/cpdfdraft.ml

open Pdfutil
open Pdfio

(* \section{Making draft documents} *)

(* Predicate on an xobject: true if an image xobject. *)
let isimage pdf (_, xobj) =
  match Pdf.lookup_direct pdf "/Subtype" xobj with 
  | Some (Pdf.Name "/Image") -> true
  | _ -> false

(* Given a set of resources for a page, and the name of a resource, determine if
that name refers to an image xobject. *)
let xobject_isimage pdf resources name =
  match resources with
  | Pdf.Dictionary _ ->
      begin match Pdf.lookup_direct pdf "/XObject" resources with
      | Some xobjects ->
          isimage pdf ("", Pdf.lookup_fail "xobject not there" pdf name xobjects)
      | _ -> false
      end
  | _ -> failwith "bad resources"

(* The subsitute for an image. *)
let substitute boxes =
  if boxes then
    rev
      [Pdfops.Op_q;
       Pdfops.Op_w 0.;
       Pdfops.Op_G 0.;
       Pdfops.Op_re (0., 0., 1., 1.);
       Pdfops.Op_m (0., 0.);
       Pdfops.Op_l (1., 1.);
       Pdfops.Op_m (0., 1.);
       Pdfops.Op_l (1., 0.);
       Pdfops.Op_S;
       Pdfops.Op_Q]
  else
    []

(* Remove references to images from a graphics stream. *)
let rec remove_images_stream onlyremove boxes pdf resources prev = function
  | [] -> rev prev
  | (Pdfops.Op_Do name) as h::t ->
      if xobject_isimage pdf resources name && (match onlyremove with None -> true | Some x -> x = name)
      then remove_images_stream onlyremove boxes pdf resources (substitute boxes @ prev) t
      else remove_images_stream onlyremove boxes pdf resources (h::prev) t
  | Pdfops.InlineImage _ as h::t ->
      if onlyremove <> None
        then remove_images_stream onlyremove boxes pdf resources (h::prev) t
        else remove_images_stream onlyremove boxes pdf resources (substitute boxes @ prev) t
  | h::t ->
      remove_images_stream onlyremove boxes pdf resources (h::prev) t

let rec process_form_xobject onlyremove boxes pdf form =
  let form = Pdf.direct pdf form in
    let page =
      {Pdfpage.content = [form];
       Pdfpage.mediabox = Pdf.Null;
       Pdfpage.resources =
         begin match Pdf.lookup_direct pdf "/Resources" form with
         | Some r -> r
         | None -> Pdf.Dictionary []
         end;
       Pdfpage.rotate = Pdfpage.Rotate0;
       Pdfpage.rest = Pdf.Dictionary []}
    in
      let page', pdf =
        remove_images_page onlyremove boxes pdf page
      in
        let form' =
          match form with
          | Pdf.Stream {contents = (dict, _)} ->
              begin match 
                Pdfops.stream_of_ops
                  (Pdfops.parse_operators pdf (Pdf.Dictionary []) page'.Pdfpage.content)
              with
              | Pdf.Stream {contents = (_, Pdf.Got data)} ->
                  let dict' =
                    Pdf.add_dict_entry dict "/Length" (Pdf.Integer (bytes_size data))
                  in
                    Pdf.Stream {contents = (dict', Pdf.Got data)}
              | _ -> assert false
              end
          | _ -> raise (Pdf.PDFError "not a stream")
        in
          form', pdf

(* Remove images from a page. *)
and remove_images_page onlyremove boxes pdf page =
  let isform pdf xobj =
    match Pdf.lookup_direct pdf "/Subtype" xobj with Some (Pdf.Name "/Form") -> true | _ -> false
  in
  let isimage pdf xobj =
    match Pdf.lookup_direct pdf "/Subtype" xobj with Some (Pdf.Name "/Image") -> true | _ -> false
  in
  (* Remove image xobjects and look into form ones *)
  let form_xobjects, image_xobjects =
    match Pdf.lookup_direct pdf "/XObject" page.Pdfpage.resources with
    | Some (Pdf.Dictionary elts) ->
        keep (function (_, p) -> isform pdf p) elts,
        keep (function (_, p) -> isimage pdf p) elts
    | _ -> [], []
  in
  let resources', pdf =
    let names, pointers = split form_xobjects in
      let form_xobjects', pdf =
        let pdf = ref pdf
        in let outputs = ref [] in
          iter
            (fun p ->
              let p', pdf' = process_form_xobject onlyremove boxes !pdf p in
                pdf := pdf';
                outputs =| p')
            pointers;
          rev !outputs, !pdf
      in
        let nums = ref [] in
          iter
            (fun xobj ->
               let objnum = Pdf.addobj pdf xobj in
                 nums =| objnum)
            form_xobjects';
        let image_xobjects' =
          match onlyremove with
            None -> []
          | Some n -> option_map (function (n', _) as xobj -> if n = n' then None else Some xobj) image_xobjects
        in
            let newdict =
              Pdf.Dictionary (image_xobjects' @ combine names (map (fun x -> Pdf.Indirect x) (rev !nums)))
            in
              Pdf.add_dict_entry page.Pdfpage.resources "/XObject" newdict, pdf
    in
      let content' =
        remove_images_stream onlyremove boxes pdf page.Pdfpage.resources []
           (Pdfops.parse_operators pdf page.Pdfpage.resources page.Pdfpage.content)
      in
        {page with
          Pdfpage.content =
            (let stream = Pdfops.stream_of_ops content' in
              Pdfcodec.encode_pdfstream pdf Pdfcodec.Flate stream;
              [stream]);
          Pdfpage.resources = resources'}, pdf

(* Remove images from all pages in a document. *)
let draft onlyremove boxes range pdf =
  let pages = Pdfpage.pages_of_pagetree pdf in
    let pagenums = indx pages in
    let pdf = ref pdf
    in let pages' = ref [] in
      iter2 
       (fun p pagenum ->
         let p', pdf' =
           if mem pagenum range
             then remove_images_page onlyremove boxes !pdf p
             else p, !pdf
         in
           pdf := pdf';
           pages' =| p')
       pages
       pagenums;
      Pdfpage.change_pages true !pdf (rev !pages')