From f80130560edd32a0a9181d3ad5a1b83fe936d61a Mon Sep 17 00:00:00 2001
From: Christopher Overbeck <coverbeck@catiglass.com>
Date: Tue, 15 Sep 2026 12:32:57 -0500
Subject: [PATCH] Regenerate viewport dimensions when the viewport view changes
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Panning, zooming, twisting or rescaling a layout viewport moves model
geometry across the sheet without touching that geometry, so nothing in
the ordinary entity-change path noticed and the dimensions drawn through
the viewport stayed where they were — detached from what they measure.

`Scene::notify_viewport_changed` announces the viewport itself as a
modified entity. That is all it takes: every trans-space reference
carries the viewport handle as the first link of its chain, so the
dependency lookup in `refresh_associative_dimensions` already finds the
associations from there, and the refresh re-places and re-measures them.

Called from each mutator that changes the paper<->model mapping: pan,
zoom, fit-to-bounds, view normalisation on entering MSPACE, the
view-direction/twist snaps, the viewcube camera path, and both
annotation-scale setters.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 src/scene/camera_ops.rs |  3 +++
 src/scene/mod.rs        |  8 ++++++++
 src/scene/mspace.rs     | 23 +++++++++++++++++++++--
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/scene/camera_ops.rs b/src/scene/camera_ops.rs
index 4c0118256..e17ebfd7f 100644
--- a/src/scene/camera_ops.rs
+++ b/src/scene/camera_ops.rs
@@ -567,6 +567,9 @@ impl Scene {
             viewport.view_target.x = center.x;
             viewport.view_target.y = center.y;
             viewport.view_target.z = center.z;
+            // Panning a viewport moves model geometry across the sheet; the
+            // dimensions drawn through it follow.
+            self.notify_viewport_changed(handle);
         } else {
             self.camera.borrow_mut().target = center;
         }
diff --git a/src/scene/mod.rs b/src/scene/mod.rs
index 452e6f822..bcb966d38 100644
--- a/src/scene/mod.rs
+++ b/src/scene/mod.rs
@@ -5296,6 +5296,10 @@ impl Scene {
         self.document
             .set_viewport_annotation_scale(viewport, scale_handle);
 
+        // Viewport scale changed: the dimensions drawn on the sheet
+        // through it measure the same model geometry at a new paper
+        // size and have to be re-placed.
+        self.notify_viewport_changed(viewport);
         self.resident_wire_sets.borrow_mut().clear();
         self.bump_geometry();
 
@@ -5349,6 +5353,10 @@ impl Scene {
         vp.view_height = vp.height / factor;
         self.document
             .set_viewport_annotation_scale(viewport, scale_handle);
+        // Viewport scale changed: the dimensions drawn on the sheet
+        // through it measure the same model geometry at a new paper
+        // size and have to be re-placed.
+        self.notify_viewport_changed(viewport);
         self.resident_wire_sets.borrow_mut().clear();
         self.bump_geometry();
         true
diff --git a/src/scene/mspace.rs b/src/scene/mspace.rs
index dc16c99f4..97814e4c7 100644
--- a/src/scene/mspace.rs
+++ b/src/scene/mspace.rs
@@ -259,6 +259,9 @@ impl Scene {
                 vp.view_height = eff_h;
             }
         }
+        // A viewport's view changed, so every dimension drawn on the
+        // sheet through it has to be re-placed and re-measured.
+        self.notify_viewport_changed(vp_handle);
     }
 
     /// Fit model-space bounds into the active floating viewport without moving
@@ -297,6 +300,7 @@ impl Scene {
                 viewport.custom_scale = viewport.height / viewport.view_height;
             }
         }
+        self.notify_viewport_changed(viewport_handle);
         self.camera_generation += 1;
         true
     }
@@ -348,6 +352,9 @@ impl Scene {
             vp.view_target.y += model_delta.y as f64;
             vp.view_target.z += model_delta.z as f64;
         }
+        // A viewport's view changed, so every dimension drawn on the
+        // sheet through it has to be re-placed and re-measured.
+        self.notify_viewport_changed(vp_handle);
     }
 
     /// Zoom the active viewport's model-space view by `steps` notches.
@@ -397,6 +404,9 @@ impl Scene {
                 }
             }
         }
+        // A viewport's view changed, so every dimension drawn on the
+        // sheet through it has to be re-placed and re-measured.
+        self.notify_viewport_changed(vp_handle);
     }
 
     /// Orbit the active viewport's view direction by the given screen-pixel delta.
@@ -474,6 +484,9 @@ impl Scene {
             vp.view_direction.z = dir.z as f64;
             vp.twist_angle = twist;
         }
+        // Twisting a viewport rotates model geometry on the sheet; the
+        // dimensions drawn through it follow.
+        self.notify_viewport_changed(vp_handle);
     }
 
     /// Mutate the active viewport's camera through a closure, then re-encode the
@@ -502,6 +515,7 @@ impl Scene {
             .normalize_or(glam::Vec3::Y);
         let roll = up0.cross(desired_up).dot(dir).atan2(up0.dot(desired_up));
         let twist = -roll as f64;
+        let mut changed = false;
         if let Some(acadrust::EntityType::Viewport(vp)) = self.document.get_entity_mut(vp_handle) {
             if vp.status.locked {
                 return false;
@@ -514,9 +528,14 @@ impl Scene {
                 tmp.projection == view::camera::Projection::Perspective;
             vp.lens_length =
                 (12.0 / (tmp.fov_y * 0.5).tan().max(1e-6)) as f64;
-            return true;
+            changed = true;
         }
-        false
+        if changed {
+            // The view (and with it the sheet placement of everything drawn
+            // through this viewport) moved.
+            self.notify_viewport_changed(vp_handle);
+        }
+        changed
     }
 
     /// Render mode of the active paper-space viewport, or `None` when no