From b897197443e40207481b6738f6c5755a74ba78d8 Mon Sep 17 00:00:00 2001
From: John Whitington <john@coherentgraphics.co.uk>
Date: Thu, 31 Oct 2024 13:17:33 +0000
Subject: [PATCH] Scaffolding for -center-to-fit

---
 cpdfcommand.ml | 18 +++++++++++++++++-
 cpdfmanual.tex |  1 +
 cpdfpage.ml    | 22 ++++++++++++++++++++++
 cpdfpage.mli   |  2 ++
 4 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index 38b17c4..5d20f82 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -106,6 +106,7 @@ type op =
   | Scale
   | ScaleToFit
   | Stretch
+  | CenterToFit
   | ScaleContents of float
   | AttachFile of string list
   | RemoveAttachedFiles
@@ -260,6 +261,7 @@ let string_of_op = function
   | Scale -> "Scale"
   | ScaleToFit -> "ScaleToFit"
   | Stretch -> "Stretch"
+  | CenterToFit -> "CenterToFit"
   | ScaleContents _ -> "ScaleContents"
   | AttachFile _ -> "AttachFile"
   | RemoveAttachedFiles -> "RemoveAttachedFiles"
@@ -930,7 +932,7 @@ let banned banlist = function
   | Rotateby _ | Upright | VFlip | HFlip | Impose _ | Chop _ | ChopHV _ | Redact ->
       mem Pdfcrypt.NoAssemble banlist
   | TwoUp | TwoUpStack | RemoveBookmarks | AddRectangle | RemoveText|
-    Draft | Shift | ShiftBoxes | Scale | ScaleToFit|Stretch|RemoveAttachedFiles|
+    Draft | Shift | ShiftBoxes | Scale | ScaleToFit|Stretch|CenterToFit|RemoveAttachedFiles|
     RemoveAnnotations|RemoveFonts|Crop|RemoveCrop|Trim|RemoveTrim|Bleed|RemoveBleed|Art|RemoveArt|
     CopyBox|MediaBox|HardBox _|SetTrapped|SetUntrapped|Presentation|
     BlackText|BlackLines|BlackFills|CopyFont _|StampOn _|StampUnder _|StampAsXObject _|
@@ -1217,6 +1219,10 @@ let setstretch s =
   setop Stretch ();
   args.coord <- s
 
+let setcenter s =
+  setop CenterToFit ();
+  args.coord <- s
+
 let setattachfile s =
   match args.op with
   | Some (AttachFile t) ->
@@ -2095,6 +2101,9 @@ let specs =
    ("-stretch",
       Arg.String setstretch,
       " -stretch \"x y\" scales without preserving aspect ratio");
+   ("-center-to-fit",
+      Arg.String setcenter,
+      " -center-to-fit \"x y\" centers pages on page size (x, y)");
    ("-scale-contents",
       Arg.Float setscalecontents,
       "  Scale contents by the given factor");
@@ -4208,6 +4217,13 @@ let go () =
           let pdf = if args.prerotate then prerotate range pdf else pdf in
           let xylist = Cpdfcoord.parse_coordinates pdf args.coord in
             write_pdf false (Cpdfpage.stretch ~fast:args.fast xylist pdf range)
+  | Some CenterToFit ->
+      let pdf = get_single_pdf args.op false in
+        let range = parse_pagespec_allow_empty pdf (get_pagespec ()) in
+          warn_prerotate range pdf;
+          let pdf = if args.prerotate then prerotate range pdf else pdf in
+          let xylist = Cpdfcoord.parse_coordinates pdf args.coord in
+            write_pdf false (Cpdfpage.center_to_fit ~fast:args.fast xylist pdf range)
   | Some (ScaleContents scale) ->
       let pdf = get_single_pdf args.op false in
         let range = parse_pagespec_allow_empty pdf (get_pagespec ()) in
diff --git a/cpdfmanual.tex b/cpdfmanual.tex
index 5de733b..8371fc2 100644
--- a/cpdfmanual.tex
+++ b/cpdfmanual.tex
@@ -1,3 +1,4 @@
+% Document -center-to-fit
 \documentclass{book}
 % Edit here to produce cpdfmanual.pdf, cpdflibmanual.pdf, pycpdfmanual.pdf,
 % dotnetcpdflibmanual.pdf, jcpdflibmanual.pdf jscpdflibmanual.pdf etc.
diff --git a/cpdfpage.ml b/cpdfpage.ml
index c53f86a..8fb4135 100644
--- a/cpdfpage.ml
+++ b/cpdfpage.ml
@@ -556,6 +556,28 @@ let stretch ?(fast=false) sxsylist pdf range =
   in
     process_pages stretch_page pdf range
 
+(* Centre page content (crop box) on given page size, with no scaling. *)
+let center_to_fit ?(fast=false) sxsylist pdf range =
+  let stretch_page pnum page =
+    let sx, sy = List.nth sxsylist (pnum - 1) in
+    let (minx, miny, maxx, maxy) =
+      Pdf.parse_rectangle
+        pdf
+        (match Pdf.lookup_direct pdf "/CropBox" page.Pdfpage.rest with
+        | Some r -> r
+        | None -> page.Pdfpage.mediabox)
+    in
+    let scale_x, scale_y = sx /. (maxx -. minx), sy /. (maxy -. miny) in
+    let f (xmin, ymin, xmax, ymax) = xmin *. scale_x, ymin *. scale_y, xmax *. scale_x, ymax *. scale_y in
+    let page = change_boxes f pdf page in
+    let matrix = Pdftransform.matrix_of_op (Pdftransform.Scale ((0., 0.), scale_x, scale_y)) in
+    let transform_op = Pdfops.Op_cm matrix in
+    let page = change_pattern_matrices_page pdf matrix page in
+      Pdfannot.transform_annotations pdf matrix page.Pdfpage.rest;
+      (Pdfpage.prepend_operators pdf ~fast [transform_op] page, pnum, matrix)
+  in
+    process_pages stretch_page pdf range
+
 (* Scale to fit page of size x * y *)
 let scale_to_fit_pdf ?(fast=false) position input_scale xylist op pdf range =
   let scale_page_to_fit pnum page =
diff --git a/cpdfpage.mli b/cpdfpage.mli
index 02c4cf1..116b090 100644
--- a/cpdfpage.mli
+++ b/cpdfpage.mli
@@ -81,6 +81,8 @@ val scale_to_fit_pdf : ?fast:bool -> Cpdfposition.position -> float -> (float *
 
 val stretch : ?fast:bool -> (float * float) list -> Pdf.t -> int list -> Pdf.t
 
+val center_to_fit : ?fast:bool -> (float * float) list -> Pdf.t -> int list -> Pdf.t
+
 (** {2 Stamping} *)
 
 (** [combine_pages fast under over scaletofit swap equalize] combines the page