From 4d358d4fa4df894d7de6f63a0cecf16d8a1bdd6a Mon Sep 17 00:00:00 2001
From: pauliusiv123-rgb <235694617+pauliusiv123-rgb@users.noreply.github.com>
Date: Thu, 15 Oct 2026 09:27:02 +0300
Subject: [PATCH] M2: a /Rotate that isn't a quarter turn counts as 0, as the
 page is drawn (#1863)
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Page::rotation rounded a /Rotate that isn't a multiple of 90 down to a
quarter turn (135 became 90), while the renderer draws such a page
upright. Display size and the display-to-user-space matrix (header and
footer, watermarks, measuring, printing, image signatures) then
disagreed with the page on screen. ISO 32000-2 §7.7.3.3 requires a
multiple of 90; read any other value as 0, as the renderer does.

Page import and image stamps, which read /Rotate themselves, already
treat such a value as 0. Test: rotate_off_a_quarter_turn_counts_as_upright
(/Rotate 135, 30, -45, 359).
---
 crates/model/README.md  |  3 ++-
 crates/model/src/lib.rs | 21 +++++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/crates/model/README.md b/crates/model/README.md
index 06c30b039..5872b2566 100644
--- a/crates/model/README.md
+++ b/crates/model/README.md
@@ -9,7 +9,8 @@ L3/L4 crates need:
   geometry, and the matrix from "display space" (points, origin at the bottom-left of the page as
   shown, after `/UserUnit` and `/Rotate`) to user space, so content can be placed the way the
   reader sees the page. `/UserUnit` is read as Acrobat reads it: the page's own entry, a number
-  from 1 up, at most 75,000; anything else counts as 1.
+  from 1 up, at most 75,000; anything else counts as 1. A `/Rotate` that isn't a multiple of 90
+  counts as 0, as the renderer draws it.
   `view_matrix_for(rotation, rect)` is the same matrix for any rectangle, e.g. to draw a
   comment's picture upright inside its user-space `/Rect` on a turned page.
 
diff --git a/crates/model/src/lib.rs b/crates/model/src/lib.rs
index 4e4f3f53b..211b44492 100644
--- a/crates/model/src/lib.rs
+++ b/crates/model/src/lib.rs
@@ -37,9 +37,11 @@ impl Page {
         }
     }
 
-    /// Clockwise rotation when displayed: 0, 90, 180 or 270.
+    /// Clockwise rotation when displayed: 0, 90, 180 or 270. A `/Rotate` that isn't a multiple
+    /// of 90 (ISO 32000-2 §7.7.3.3 requires one) counts as 0, as the renderer draws that page.
     pub fn rotation(&self, doc: &Document) -> i64 {
-        self.dict.get(b"Rotate").and_then(|o| doc.resolve(o).as_int()).unwrap_or(0).rem_euclid(360) / 90 * 90
+        let r = self.dict.get(b"Rotate").and_then(|o| doc.resolve(o).as_int()).unwrap_or(0).rem_euclid(360);
+        if r % 90 == 0 { r } else { 0 }
     }
 
     /// The size of the page's user-space unit in points (`/UserUnit`; it isn't inherited), read
@@ -184,6 +186,21 @@ mod tests {
         }
     }
 
+    /// A `/Rotate` that isn't a quarter turn counts as 0, as the renderer draws the page
+    /// upright, so display space matches what's on screen.
+    #[test]
+    fn rotate_off_a_quarter_turn_counts_as_upright() {
+        for rotate in [135, 30, -45, 359] {
+            let d = doc(rotate);
+            let p = &pages(&d)[0];
+            assert_eq!(p.rotation(&d), 0, "{rotate}");
+            assert_eq!(p.display_size(&d), (200.0, 300.0), "{rotate}");
+            assert_eq!(p.view_matrix(&d), [1.0, 0.0, 0.0, 1.0, 10.0, 20.0], "{rotate}");
+        }
+        let d = doc(-90);
+        assert_eq!(pages(&d)[0].rotation(&d), 270);
+    }
+
     /// Display space is in points: `/UserUnit 2` doubles it. As in Acrobat, the value isn't
     /// inherited, values below 1 or not numbers count as 1, and values over 75,000 as 75,000.
     #[test]