Adds -stretch implmentation

cpdfpage.ml

@@ -534,8 +534,27 @@ let scale_pdf ?(fast=false) sxsylist pdf range =
       in
         process_pages scale_page pdf range
 
-let stretch ?(fast=false) xylist pdf range =
+(* Scale without regard to aspect ratio. *)
-  pdf
+let stretch ?(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 =