fix(annot): a 3D poster fitted to its rectangle with rounding is taken

A poster box fitted to the annotation rectangle in floating point can
end a few ulps outside it (a 7x3 picture centred in 0 100 3.6 110.8
spans -2.2e-16 to 3.6000000000000005), and the exact containment check
refused it. The check now allows a slack of 1e-9 of the rectangle's
largest coordinate, clamps the box to the rectangle, and only then
requires it to have width and height, so a box wholly within the slack
outside the rectangle is still refused.

Tests: a_3d_poster_fitted_to_its_rectangle_with_rounding_is_taken
fails without the slack (Invalid); the new case in
a_3d_poster_outside_its_rectangle_or_without_a_size_is_refused fails
when the size check runs before the clamp.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9

crates/annot/src/tests.rs

@@ -2296,6 +2296,7 @@ fn a_3d_poster_outside_its_rectangle_or_without_a_size_is_refused() {
         (picture([50.0, 100.0, 250.0, 300.0], (10.0, 10.0)), "starts left of the rectangle"),
         (picture([100.0, 100.0, 300.0, 301.0], (10.0, 10.0)), "ends above it"),
         (picture([100.0, 100.0, 300.0, 300.0], (0.0, 10.0)), "has no width"),
+        (picture([100.0 - 2e-7, 150.0, 100.0 - 1e-7, 200.0], (10.0, 10.0)), "lies outside within the rounding slack"),
     ] {
         let mut doc = fixture();
         let new = NewModel3d {
@@ -2310,3 +2311,22 @@ fn a_3d_poster_outside_its_rectangle_or_without_a_size_is_refused() {
         assert_eq!(list(&doc, 0).len(), 1, "{why}: nothing added");
     }
 }
+
+/// A poster box fitted to the rectangle in floating point ends an ulp outside it: a 7×3 picture
+/// centred in [0 100 3.6 110.8] spans -2.2e-16 to 3.6000000000000005. It is taken, inside the
+/// rectangle.
+#[test]
+fn a_3d_poster_fitted_to_its_rectangle_with_rounding_is_taken() {
+    let mut doc = fixture();
+    let at = [-2.220446049250313e-16, 104.62857142857143, 3.6000000000000005, 106.17142857142858];
+    let poster = PosterPicture { xobject: ObjRef { num: 6, generation: 0 }, image: false, size: (7.0, 3.0), at };
+    let new = NewModel3d {
+        page: 0,
+        rect: [0.0, 100.0, 3.6, 110.8],
+        model: b"PRC rest",
+        activation: Activation3d::default(),
+        poster: Some(poster),
+        contents: "",
+    };
+    assert_eq!(add_3d_model(&mut doc, &new, &meta("m")), Ok(1));
+}

crates/annot/src/threed.rs

@@ -199,8 +199,11 @@ fn annotation_dict(new: &NewModel3d<'_>, rect: [f64; 4], page: ObjRef, stream: O
 /// The poster drawing `p` into its box, which must lie within `rect`.
 fn picture_poster(rect: [f64; 4], p: &PosterPicture) -> Result<Stream, AnnotError> {
     let at = normalize(p.at);
-    let inside = finite(&p.at) && at[0] >= rect[0] && at[1] >= rect[1] && at[2] <= rect[2] && at[3] <= rect[3] && at[2] > at[0] && at[3] > at[1];
-    if !inside {
+    // A box fitted to `rect` in floating point can end a few ulps outside it: allow that, then clamp.
+    let slack = rect.iter().fold(1.0_f64, |m, v| m.max(v.abs())) * 1e-9;
+    let near = finite(&p.at) && at[0] >= rect[0] - slack && at[1] >= rect[1] - slack && at[2] <= rect[2] + slack && at[3] <= rect[3] + slack;
+    let at = [at[0].max(rect[0]), at[1].max(rect[1]), at[2].min(rect[2]), at[3].min(rect[3])];
+    if !(near && at[2] > at[0] && at[3] > at[1]) {
         return Err(AnnotError::Invalid("the poster must fit inside the 3D model's rectangle".into()));
     }
     let place = appearance::picture_place(at, p.image, Some(p.size)).ok_or_else(|| AnnotError::Invalid("the poster picture has no size".into()))?;