From b32e0a3e27142898e87e13464154d4f9d8c5e96e Mon Sep 17 00:00:00 2001
From: LEdoian <paperjam@pokemon.ledoian.cz>
Date: Sat, 2 Mar 2024 01:20:25 +0100
Subject: [PATCH] Implemented interleave

---
SPDX-License-Identifier: GPL-2.0-or-later

 cmds.cc        | 39 +++++++++++++++++++++++++++++++++++++++
 paperjam.1.txt | 10 ++++++++++
 2 files changed, 49 insertions(+)

diff --git a/cmds.cc b/cmds.cc
index a2ac331..49590a5 100644
--- a/cmds.cc
+++ b/cmds.cc
@@ -2,6 +2,7 @@
  *	PaperJam -- Commands
  *
  *	(c) 2018--2022 Martin Mares <mj@ucw.cz>
+ *	(c) 2024 LEdoian <paperjam@pokemon.ledoian.cz>
  */
 
 #include <cassert>
@@ -1490,6 +1491,42 @@ static const arg_def slice_args[] = {
   { NULL,	0,				NULL }
 };
 
+/*** interleave ***/
+
+class interleave_cmd : public cmd_exec {
+  int n;
+public:
+  interleave_cmd(cmd *c)
+    {
+      n = c->arg("n")->as_int(0);
+      if (n <= 0)
+	err("The number of interleaving groups must be positive");
+    }
+  vector<page *> process(vector<page *> &pages) override;
+};
+
+vector<page *> interleave_cmd::process(vector<page *> &pages)
+{
+  vector<page *> in, out;
+
+  in = pages;
+  // The last page may be superfluous...
+  while (in.size() % n)
+    in.push_back(new empty_page(in[0]->width, in[0]->height));
+  int split = (int) in.size() / n;
+
+  for (int i=0; i<split; i++)
+    for (int j=0; j<n; j++)
+       out.push_back(in[j*split+i]);
+
+  return out;
+}
+
+static const arg_def interleave_args[] = {
+  { "n",	AT_INT | AT_POSITIONAL | AT_MANDATORY,	"Number of interleaving groups" },
+  { NULL,	0,					NULL }
+};
+
 /*** Command table ***/
 
 template<typename T> cmd_exec *ctor(cmd *c) { return new T(c); }
@@ -1515,6 +1552,8 @@ const cmd_def cmd_table[] = {
 		"Fit image to a given paper" },
   { "flip",	flip_args,	0,	&ctor<flip_cmd>,
 		"Flip page horizontally and/or vertically" },
+  { "interleave",	interleave_args,	0,	&ctor<interleave_cmd>,
+		"Interleave pages from different parts of the document" },
   { "margins",	margins_args,	0,	&ctor<margins_cmd>,
 		"Define image box by dimensions of margins around it" },
   { "merge",	no_args,	0,	&ctor<merge_cmd>,
diff --git a/paperjam.1.txt b/paperjam.1.txt
index 94f3432..9bebcd4 100644
--- a/paperjam.1.txt
+++ b/paperjam.1.txt
@@ -255,6 +255,16 @@ Flip pages horizontally or vertically.
 *v=*'switch'::
 	Flip vertically.
 
+interleave
+~~~~~~~~~~
+Splits the document into n groups of same size and interleaves them (first page
+from all groups, then second, ...).
+
+If the number of input pages is not divisible by n, blank pages are added.
+
+*n=*'number'::
+	Number of groups.
+
 margins
 ~~~~~~~
 Define a new image box by dimensions of margins around it. More technically,
-- 
2.43.0