From c04627eae8625801146458d33c8b0e7baa5797a0 Mon Sep 17 00:00:00 2001
From: John Whitington <john@coherentgraphics.co.uk>
Date: Tue, 11 Apr 2023 16:08:51 +0100
Subject: [PATCH] Soft mask transformation procedure

---
 cpdfpage.ml | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 4 deletions(-)

diff --git a/cpdfpage.ml b/cpdfpage.ml
index 39021a6..43e3426 100644
--- a/cpdfpage.ml
+++ b/cpdfpage.ml
@@ -4,10 +4,80 @@ open Cpdferror
 (* FIXME: Need to take account of inherited resources (among Xobjects and their children - pages
    are regularized upon loading). Would be nice to see a failing example first though.
    FIXME: What would happen if a pattern was used in a transforming and non-transforming way - we
-   would have to depulicate - again, no failing example available.
+   would have to dedupulicate - again, no failing example available.
    FIXME: combine change_annotation_matrices, change_pattern_matrices and change_softmask_matrices
    into one *)
 
+(* Transparency group soft masks appear to need altering with the inverse of
+   the transformation matrix. We find them all, deduplicate, and then process
+   in place. *)
+
+(* FIXME sub-xobjects! *)
+(* For each xobject, look in /Resources -> /ExtGState -> /G, and get object number. *)
+let rec change_softmask_matrices_xobject pdf xobject =
+  Printf.printf "change_softmask_matrices_xobject: %s\n" (Pdfwrite.string_of_pdf xobject);
+  let objnums = ref [] in
+    begin match xobject with
+    | Pdf.Indirect i ->
+        let dict = Pdf.lookup_obj pdf i in
+          begin match Pdf.lookup_direct pdf "/Resources" dict with
+          | Some d ->
+              begin match Pdf.lookup_direct pdf "/ExtGState" d with
+              | Some (Pdf.Dictionary extgstates) ->
+                  Printf.printf "Found %i extgstates to examine\n" (length extgstates);
+                  iter
+                    (function extgstate ->
+                       match Pdf.direct pdf extgstate with
+                       | Pdf.Dictionary d ->
+                           begin match lookup "/SMask" d with
+                           | Some (Pdf.Dictionary d) ->
+                               begin match lookup "/G" d with
+                               | Some (Pdf.Indirect i) ->
+                                   Printf.printf "Collecting objnum %i\n" i;
+                                   objnums := i::!objnums
+                               | _ -> ()
+                               end
+                           | _ -> ()
+                           end
+                       | _ -> ())
+                    (map snd extgstates)
+              | _ -> ()
+              end
+          | _ -> ()
+          end
+    | _ -> ()
+    end;
+    let subxobjects =
+      match Pdf.lookup_direct pdf "/Resources" xobject with
+      | Some d ->
+          begin match Pdf.lookup_direct pdf "/XObject" d with
+          | Some (Pdf.Dictionary d) -> map snd d
+          | _ -> []
+          end
+      | _ -> []
+    in
+    let descendants =
+      flatten (map (change_softmask_matrices_xobject pdf) subxobjects)
+    in
+     descendants @ !objnums
+
+let change_softmask_matrices_page pdf tr page =
+  let xobjects =
+    match Pdf.lookup_direct pdf "/XObject" page.Pdfpage.resources with
+    | Some (Pdf.Dictionary d) -> d
+    | _ -> []
+  in
+    Printf.printf "** page has %i xobjects to process\n" (length xobjects);
+    let objnums = setify (flatten (map (change_softmask_matrices_xobject pdf) (map snd xobjects))) in
+      iter
+        (fun objnum ->
+           let dict = Pdf.lookup_obj pdf objnum in
+           let matrix = Pdf.parse_matrix pdf "/Matrix" dict in
+           let matrix' = Pdftransform.matrix_compose (Pdftransform.matrix_invert tr) matrix in
+           let dict = Pdf.add_dict_entry dict "/Matrix" (Pdf.make_matrix matrix') in
+             Pdf.addobj_given_num pdf (objnum, dict))
+        objnums
+
 (* When we transform a page by wrapping in an [Op_cm], we must also
 change any /Matrix entries in (some) pattern dictionaries, including inside
 xobjects. We only change the ones used with scn, to avoid pattern dictionaries
@@ -76,15 +146,14 @@ and change_pattern_matrices_xobject pdf tr xobj xobjnum =
   | _ -> ()
 
 let change_pattern_matrices_page pdf tr page =
+  change_softmask_matrices_page pdf tr page;
   let used = patterns_used pdf page.Pdfpage.content page.Pdfpage.resources in
     Printf.printf "Patterns for translation, due to being used as cs / CS";
     Hashtbl.iter (fun x _ -> Printf.printf "%s " x) used;
     Printf.printf "\n";
     {page with Pdfpage.resources = change_pattern_matrices_resources pdf tr page.Pdfpage.resources used}
 
-(* Transparency group soft masks appear to need altering with the inverse of the transformation matrix. We
-find them all, deduplicate, and then process in place. *)
-let change_softmask_matrices_page pdf tr page = ()
+(* Concatenate inverse matrix to each /Matrix entry in those object numbers. *)
 
 (* Output information for each page *)
 let output_page_info pdf range =