From 6ff43c0f084b2ca5356ee6710b23fd751ce94749 Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Fri, 10 Aug 2018 15:12:16 +0200
Subject: Make fz_page objects singleton.

Keep a list of currently open pages for each document. Attempting to
load a page that is already loaded will return the same instance again.
---
 include/mupdf/fitz/document.h |  3 +++
 source/fitz/document.c        | 26 +++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/mupdf/fitz/document.h b/include/mupdf/fitz/document.h
index 3e6ac1e9..9b506cba 100644
--- a/include/mupdf/fitz/document.h
+++ b/include/mupdf/fitz/document.h
@@ -209,6 +209,7 @@ struct fz_annot_s
 struct fz_page_s
 {
 	int refs;
+	int number; /* page number */
 	fz_page_drop_page_fn *drop_page;
 	fz_page_bound_page_fn *bound_page;
 	fz_page_run_page_contents_fn *run_page_contents;
@@ -219,6 +220,7 @@ struct fz_page_s
 	fz_page_separation_disabled_fn *separation_disabled;
 	fz_page_separations_fn *separations;
 	fz_page_uses_overprint_fn *overprint;
+	fz_page **prev, *next; /* linked list of currently open pages */
 };
 
 /*
@@ -245,6 +247,7 @@ struct fz_document_s
 	fz_document_output_intent_fn *get_output_intent;
 	int did_layout;
 	int is_reflowable;
+	fz_page *open; /* linked list of currently open pages */
 };
 
 /*
diff --git a/source/fitz/document.c b/source/fitz/document.c
index 013badb0..26ae93ea 100644
--- a/source/fitz/document.c
+++ b/source/fitz/document.c
@@ -319,9 +319,27 @@ fz_document_output_intent(fz_context *ctx, fz_document *doc)
 fz_page *
 fz_load_page(fz_context *ctx, fz_document *doc, int number)
 {
+	fz_page *page;
+
 	fz_ensure_layout(ctx, doc);
+
+	for (page = doc->open; page; page = page->next)
+		if (page->number == number)
+			return fz_keep_page(ctx, page);
+
 	if (doc && doc->load_page)
-		return doc->load_page(ctx, doc, number);
+	{
+		page = doc->load_page(ctx, doc, number);
+		page->number = number;
+
+		/* Insert new page at the head of the list of open pages. */
+		if ((page->next = doc->open) != NULL)
+			doc->open->prev = &page->next;
+		doc->open = page;
+		page->prev = &doc->open;
+		return page;
+	}
+
 	return NULL;
 }
 
@@ -472,8 +490,14 @@ fz_drop_page(fz_context *ctx, fz_page *page)
 {
 	if (fz_drop_imp(ctx, page, &page->refs))
 	{
+		/* Remove page from the list of open pages */
+		if (page->next != NULL)
+			page->next->prev = page->prev;
+		*page->prev = page->next;
+
 		if (page->drop_page)
 			page->drop_page(ctx, page);
+
 		fz_free(ctx, page);
 	}
 }
-- 
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