From 4fffab4ad3221e7aa93c1f7bee1b0c51561d069f Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 5 May 2022 11:15:45 +0200
Subject: [PATCH] Add (basic) support for Spread modes in PresentationMode
 (issue 14749)

After recent changes, adding *basic* Spread mode support in PresentationMode has now become reasonably straightforward.

However, documents with *varying* page sizes are non-trivial to handle and would require re-writing (or at least re-factoring) a bunch of the zooming-code.
Hence this PR *purposely* only allow Spread modes to be used, in PresentationMode, for documents where all pages have exactly the same size. While this obviously isn't a fully complete solution, it will however cover the vast majority of all documents and should hopefully be deemed good enough for now.
---
 web/pdf_presentation_mode.js | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/web/pdf_presentation_mode.js b/web/pdf_presentation_mode.js
index 912d3a202..7da3719cb 100644
--- a/web/pdf_presentation_mode.js
+++ b/web/pdf_presentation_mode.js
@@ -78,9 +78,20 @@ class PDFPresentationMode {
       pageNumber: pdfViewer.currentPageNumber,
       scaleValue: pdfViewer.currentScaleValue,
       scrollMode: pdfViewer.scrollMode,
-      spreadMode: pdfViewer.spreadMode,
+      spreadMode: null,
     };
 
+    if (
+      pdfViewer.spreadMode !== SpreadMode.NONE &&
+      !(pdfViewer.pageViewsReady && pdfViewer.hasEqualPageSizes)
+    ) {
+      console.warn(
+        "Ignoring Spread modes when entering PresentationMode, " +
+          "since the document may contain varying page sizes."
+      );
+      this.#args.spreadMode = pdfViewer.spreadMode;
+    }
+
     try {
       await promise;
       return true;
@@ -151,7 +162,9 @@ class PDFPresentationMode {
     // Presentation Mode, by waiting until fullscreen mode in enabled.
     setTimeout(() => {
       this.pdfViewer.scrollMode = ScrollMode.PAGE;
-      this.pdfViewer.spreadMode = SpreadMode.NONE;
+      if (this.#args.spreadMode !== null) {
+        this.pdfViewer.spreadMode = SpreadMode.NONE;
+      }
       this.pdfViewer.currentPageNumber = this.#args.pageNumber;
       this.pdfViewer.currentScaleValue = "page-fit";
     }, 0);
@@ -177,7 +190,9 @@ class PDFPresentationMode {
       this.#notifyStateChange(PresentationModeState.NORMAL);
 
       this.pdfViewer.scrollMode = this.#args.scrollMode;
-      this.pdfViewer.spreadMode = this.#args.spreadMode;
+      if (this.#args.spreadMode !== null) {
+        this.pdfViewer.spreadMode = this.#args.spreadMode;
+      }
       this.pdfViewer.currentScaleValue = this.#args.scaleValue;
       this.pdfViewer.currentPageNumber = pageNumber;
       this.#args = null;