View backgrounds: reference blend, image adjust, layouts, cleanup, style name

- Gradients: the middle colour sits (horizon - 0.5) viewport widths from the
  centre and blends over height viewport heights each side; two colours
  blend over a viewport height each side.
- Image backgrounds: offset in device pixels (right, down), negative scale
  mirrors, fitted with aspect ratio covers the viewport; the dialog keeps an
  image's offset and scale.
- Layouts: a model-space view restored on a sheet asks for the viewport,
  enters it and gives it the view's camera, background and visual style;
  inside a viewport the view goes there; a paper-space view's background is
  kept on the sheet viewport but not drawn; floating viewports draw their
  background.
- Background objects no view or viewport uses any more are erased; a view
  without a background restored where the viewport already is leaves the
  viewport's background.
- The viewport's named visual style (Realistic, ...) shows by name and the
  render-mode picker records its style on the viewport record.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/commands/layerprops.rs

@@ -891,7 +891,8 @@ impl OpenCADStudio {
                             self.command_line
                                 .push_error(crate::t!("Usage: VIEW DELETE <name>").as_ref());
                         } else {
-                            if self.tabs[i].scene.document.views.remove(&name).is_some() {
+                            if let Some(view) = self.tabs[i].scene.document.views.remove(&name) {
+                                crate::scene::erase_background(&mut self.tabs[i].scene.document, view.background_handle);
                                 self.command_line
                                     .push_output(crate::tf!("View '{}' deleted.", name).as_ref());
                             } else {

src/app/commands/view_presets.rs

@@ -53,12 +53,33 @@ impl OpenCADStudio {
                     .to_string(),
                 visual_style: name_of(&visual_styles, view.visual_style_handle),
                 live_section: name_of(&live_sections, view.live_section_handle),
+                paper_space: view.paper_space,
             })
             .collect();
+        let scene = &self.tabs[i].scene;
+        let sheet_viewports = (scene.current_layout != "Model" && scene.active_viewport.is_none()).then(|| {
+            scene
+                .layout_content_viewports()
+                .iter()
+                .filter_map(|handle| match document.get_entity(*handle) {
+                    Some(codec::EntityType::Viewport(value)) => Some((
+                        handle.value(),
+                        [
+                            value.center.x - value.width / 2.0,
+                            value.center.y - value.height / 2.0,
+                            value.center.x + value.width / 2.0,
+                            value.center.y + value.height / 2.0,
+                        ],
+                    )),
+                    _ => None,
+                })
+                .collect()
+        });
         ViewNames {
             views,
             visual_styles: visual_styles.into_iter().map(|(name, _)| name).collect(),
             live_sections: live_sections.into_iter().map(|(name, _)| name).collect(),
+            sheet_viewports,
         }
     }
 
@@ -132,16 +153,40 @@ impl OpenCADStudio {
                 if !doomed.is_empty() {
                     self.push_undo_snapshot(i, "-VIEW");
                     for name in &doomed {
-                        self.tabs[i].scene.document.views.remove(name);
+                        let removed = self.tabs[i].scene.document.views.remove(name);
+                        if let Some(view) = removed {
+                            crate::scene::erase_background(&mut self.tabs[i].scene.document, view.background_handle);
+                        }
                         self.tabs[i].scene.document.delete_layer_state(&snapshot_name(name));
                     }
                     self.tabs[i].dirty = true;
                 }
             }
+            "RESTOREVP" => {
+                let (name, handle) = arg.split_once('\u{1f}').unwrap_or((arg, ""));
+                let Some(view) = self.tabs[i].scene.document.views.get(name).cloned() else {
+                    return Task::none();
+                };
+                let Some(handle) = u64::from_str_radix(handle, 16).ok().map(Handle::new) else {
+                    return Task::none();
+                };
+                // The reference enters the selected viewport and restores the
+                // view in it.
+                let task = self.update(Message::EnterViewport(handle));
+                self.restore_view_in_active_viewport(i, &view);
+                return task;
+            }
             "RESTORE" => {
                 let Some(view) = self.tabs[i].scene.document.views.get(arg).cloned() else {
                     return Task::none();
                 };
+                if self.tabs[i].scene.current_layout != "Model"
+                    && self.tabs[i].scene.active_viewport.is_some()
+                    && !view.paper_space
+                {
+                    self.restore_view_in_active_viewport(i, &view);
+                    return Task::none();
+                }
                 let before = self.tabs[i].scene.active_gaze_dir();
                 self.tabs[i].scene.restore_named_view(&view);
                 self.apply_view_render_mode(i, &view);
@@ -250,6 +295,22 @@ impl OpenCADStudio {
         }
     }
 
+    /// A model-space view restored in the entered paper-space viewport, with
+    /// its background and visual style.
+    fn restore_view_in_active_viewport(&mut self, i: usize, view: &codec::tables::View) {
+        let Some(viewport) = self.tabs[i].scene.active_viewport else { return };
+        self.tabs[i].scene.restore_named_view_in_viewport(view, viewport);
+        if let Some(ObjectType::VisualStyle(style)) =
+            self.tabs[i].scene.document.objects.get(&view.visual_style_handle)
+        {
+            if let Some((mode, _)) = crate::modules::view::visual_style::mode_for_style_name(&style.description) {
+                self.tabs[i].scene.set_active_viewport_render_mode(mode);
+                self.tabs[i].scene.bump_geometry_no_blocks();
+            }
+        }
+        self.tabs[i].dirty = true;
+    }
+
     /// Add or replace a named view, keeping the record (and so its settings)
     /// of a view saved again under the same name.
     fn save_named_view(&mut self, i: usize, mut view: codec::tables::View) {
@@ -257,6 +318,7 @@ impl OpenCADStudio {
         let background = self.tabs[i].scene.active_background();
         let document = &mut self.tabs[i].scene.document;
         view.background_handle = crate::scene::copy_background(document, background);
+        let mut replaced = Handle::NULL;
         match document.views.get(&view.name).cloned() {
             Some(old) => {
                 view.name = old.name;
@@ -268,6 +330,7 @@ impl OpenCADStudio {
                 if view.background_handle.is_null() {
                     view.background_handle = old.background_handle;
                 }
+                replaced = old.background_handle;
             }
             None => {
                 view.handle = document.allocate_handle();
@@ -280,6 +343,7 @@ impl OpenCADStudio {
             }
         }
         document.views.add_or_replace(view);
+        crate::scene::erase_background(document, replaced);
         self.tabs[i].dirty = true;
     }
 
@@ -290,6 +354,7 @@ impl OpenCADStudio {
         };
         self.push_undo_snapshot(i, "-VIEW");
         let document = &mut self.tabs[i].scene.document;
+        let mut replaced = Handle::NULL;
         if view.handle.is_null() {
             view.handle = document.allocate_handle();
         }
@@ -297,7 +362,7 @@ impl OpenCADStudio {
             list.into_iter().find(|(entry, _)| entry.eq_ignore_ascii_case(value)).map_or(Handle::NULL, |(_, h)| h)
         };
         match setting {
-            "BACKGROUND" => view.background_handle = Handle::NULL,
+            "BACKGROUND" => replaced = std::mem::replace(&mut view.background_handle, Handle::NULL),
             "VISUALSTYLE" => view.visual_style_handle = find(crate::io::visual_styles::offered(document)),
             "SECTION" => {
                 let sections: Vec<(String, Handle)> = document
@@ -351,6 +416,7 @@ impl OpenCADStudio {
             _ => {}
         }
         document.views.add_or_replace(view);
+        crate::scene::erase_background(document, replaced);
         self.tabs[i].dirty = true;
     }
 }
@@ -381,6 +447,8 @@ impl OpenCADStudio {
             image: String::new(),
             position: BgPosition::Center,
             aspect: false,
+            offset: [0.0, 0.0],
+            scale: [1.0, 1.0],
             canvas: [0, 1, 2].map(|k| (canvas[k].clamp(0.0, 1.0) * 255.0).round() as u8),
         };
         let document = &self.tabs[i].scene.document;
@@ -407,6 +475,8 @@ impl OpenCADStudio {
                         BgPosition::Center
                     };
                     state.aspect = value.maintain_aspect_ratio;
+                    state.offset = [value.offset.x, value.offset.y];
+                    state.scale = [value.scale.x, value.scale.y];
                 }
                 _ => {}
             }
@@ -518,8 +588,8 @@ impl OpenCADStudio {
                             fit_to_screen: state.position == BgPosition::Stretch,
                             maintain_aspect_ratio: state.aspect,
                             use_tiling: state.position == BgPosition::Tile,
-                            offset: codec::types::Vector2::new(0.0, 0.0),
-                            scale: codec::types::Vector2::new(1.0, 1.0),
+                            offset: codec::types::Vector2::new(state.offset[0], state.offset[1]),
+                            scale: codec::types::Vector2::new(state.scale[0], state.scale[1]),
                         }))
                     }
                 };
@@ -533,7 +603,8 @@ impl OpenCADStudio {
                         crate::scene::add_background(document, data)
                     });
                     if let Some(view) = document.views.get_mut(&name) {
-                        view.background_handle = handle;
+                        let old = std::mem::replace(&mut view.background_handle, handle);
+                        crate::scene::erase_background(document, old);
                     }
                     self.tabs[i].dirty = true;
                 }
@@ -549,7 +620,6 @@ impl OpenCADStudio {
     /// A restored view's visual style becomes the model tab's render mode
     /// (the closest of OCS's modes); a view without one leaves it.
     pub(crate) fn apply_view_render_mode(&mut self, i: usize, view: &codec::tables::View) {
-        use codec::entities::ViewportRenderMode as M;
         if self.tabs[i].scene.current_layout != "Model" {
             return;
         }
@@ -558,19 +628,12 @@ impl OpenCADStudio {
         else {
             return;
         };
-        let (mode, label) = match style.description.as_str() {
-            "2dWireframe" => (M::Wireframe2D, "Wireframe 2D"),
-            "Wireframe" => (M::Wireframe3D, "Wireframe 3D"),
-            "Hidden" => (M::HiddenLine, "Hidden Line"),
-            "Flat" => (M::FlatShaded, "Flat Shaded"),
-            "FlatWithEdges" => (M::FlatShadedWithEdges, "Flat Shaded + Edges"),
-            "GouraudWithEdges" | "Shaded with edges" => {
-                (M::GouraudShadedWithEdges, "Gouraud Shaded + Edges")
-            }
-            "Gouraud" | "Realistic" | "Shaded" | "Conceptual" | "Shades of Gray" | "Sketchy"
-            | "X-Ray" => (M::GouraudShaded, "Gouraud Shaded"),
-            _ => return,
+        use crate::modules::view::visual_style;
+        let Some((mode, named)) = visual_style::mode_for_style_name(&style.description) else {
+            return;
         };
-        self.apply_render_mode(i, mode, label);
+        // A style of its own keeps its name; the render modes keep theirs.
+        let label = if named { style.description.clone() } else { visual_style::label_for(mode).to_string() };
+        self.apply_render_mode(i, mode, &label);
     }
 }

src/app/update/viewport.rs

@@ -1091,6 +1091,10 @@ impl OpenCADStudio {
             return Task::none();
         }
         self.apply_render_mode(i, mode, label);
+        // The viewport record carries the style the mode is saved as.
+        self.tabs[i]
+            .scene
+            .set_active_visual_style_named(crate::modules::view::visual_style::style_name_for(mode));
         self.command_line
             .push_output(crate::tf!("Visual style: {label}").as_ref());
         // The point cloud move gizmo follows the visual style.

src/app/view/controls.rs

@@ -30,6 +30,7 @@ pub(super) fn viewport_controls<'a>(
     tile_count: usize,
     render_mode_menu_open: bool,
     render_mode_preview: Option<codec::entities::ViewportRenderMode>,
+    style_name: Option<String>,
 ) -> Element<'a, Message> {
     let render_modes: Vec<RenderModeChoice> = crate::modules::view::visual_style::VISUAL_STYLES
         .iter()
@@ -98,7 +99,7 @@ pub(super) fn viewport_controls<'a>(
     // flyout keeps the current style unchanged while hovering; a click commits.
     let picker_head = button(
         row![
-            text(RenderModeChoice(render_mode).to_string()).size(11),
+            text(style_name.unwrap_or_else(|| RenderModeChoice(render_mode).to_string())).size(11),
             crate::ui::icons::themed_arrow_toggle(render_mode_menu_open, 9.0),
         ]
         .spacing(6)
@@ -379,7 +380,7 @@ mod tests {
     #[test]
     fn test_viewport_controls_construction() {
         for style in crate::modules::view::visual_style::VISUAL_STYLES {
-            let _el = viewport_controls(style.mode, true, true, true, 1, false, None);
+            let _el = viewport_controls(style.mode, true, true, true, 1, false, None, None);
             let _el_open = viewport_controls(
                 style.mode,
                 false,
@@ -388,6 +389,7 @@ mod tests {
                 2,
                 true,
                 Some(M::Wireframe3D),
+                None,
             );
         }
     }

src/app/view/mod.rs

@@ -1297,6 +1297,18 @@ bg={bg_ms:.1}ms n={view_count}"
                 let rect = tab.scene.active_model_tile_bounds(vw, vh);
                 // Unified control chip: split buttons + render-mode picker +
                 // grid / grid-snap toggles, for the active Model tile.
+                // A named style (Realistic, …) the tile draws as shows by name.
+                let style_name = match tab.scene.document.objects.get(&tab.scene.active_visual_style()) {
+                    Some(codec::objects::ObjectType::VisualStyle(style)) => {
+                        match crate::modules::view::visual_style::mode_for_style_name(&style.description) {
+                            Some((mode, true)) if mode == tab.render_mode => {
+                                Some(crate::t!(style.description.as_str()).into_owned())
+                            }
+                            _ => None,
+                        }
+                    }
+                    _ => None,
+                };
                 let bar = viewport_controls(
                     tab.render_mode,
                     self.show_grid,
@@ -1305,6 +1317,7 @@ bg={bg_ms:.1}ms n={view_count}"
                     tab.scene.model_tiles.borrow().len(),
                     self.render_mode_menu_open,
                     self.render_mode_preview,
+                    style_name,
                 );
                 // Adaptive: DensitySwap measures the bar's real width every frame
                 // (reported into `render_bar_w`, which the ViewCube reads to decide
@@ -1397,6 +1410,7 @@ bg={bg_ms:.1}ms n={view_count}"
                     0,
                     self.render_mode_menu_open,
                     self.render_mode_preview,
+                    None,
                 );
                 let adaptive: Element<'_, Message> = DensitySwap::new(vec![
                     iced::widget::opaque(bar),

src/modules/view/view_cmd.rs

@@ -57,6 +57,8 @@ pub struct ViewInfo {
     pub category: String,
     pub visual_style: Option<String>,
     pub live_section: Option<String>,
+    /// Saved in paper space.
+    pub paper_space: bool,
 }
 
 /// What -VIEW checks typed names against.
@@ -65,6 +67,10 @@ pub struct ViewNames {
     pub views: Vec<ViewInfo>,
     pub visual_styles: Vec<String>,
     pub live_sections: Vec<String>,
+    /// On a layout's sheet (no viewport entered): the layout's viewports as
+    /// (handle, [min x, min y, max x, max y]), one of which takes a
+    /// model-space view being restored.
+    pub sheet_viewports: Option<Vec<(u64, [f64; 4])>>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
@@ -106,6 +112,7 @@ enum Step {
     List,
     Delete,
     Restore,
+    RestoreViewport(String),
     Save,
     WindowName,
     WindowFirst(String),
@@ -350,6 +357,7 @@ impl CadCommand for DashViewCommand {
             Step::List | Step::SettingViewList(_) => "Enter view name(s) to list <*>:".into(),
             Step::Delete => "Enter view name(s) to delete:".into(),
             Step::Restore => "Enter view name to restore:".into(),
+            Step::RestoreViewport(_) => "Select Viewport for view:".into(),
             Step::Save | Step::WindowName => "Enter view name to save:".into(),
             Step::WindowFirst(_) => "Specify first corner:".into(),
             Step::WindowSecond(..) => "Specify opposite corner:".into(),
@@ -421,9 +429,19 @@ impl CadCommand for DashViewCommand {
                 }
             }
             Step::Restore => match self.view(t) {
+                // On a sheet a model-space view goes into a viewport the
+                // user selects.
+                Some(view) if !view.paper_space && self.names.sheet_viewports.is_some() => {
+                    self.step = Step::RestoreViewport(view.name.clone());
+                    CmdResult::ReportMeasurement("Restoring Model space view.".into())
+                }
                 Some(view) => CmdResult::Dispatch(format!("-VIEW >RESTORE {}", view.name)),
                 None => Self::end(&format!("Cannot find view \"{t}\".")),
             },
+            Step::RestoreViewport(name) => {
+                self.step = Step::RestoreViewport(name);
+                CmdResult::ReportError("*Invalid selection*".into())
+            }
             Step::Save => CmdResult::Dispatch(format!("-VIEW >SAVE {t}")),
             Step::WindowName => {
                 self.step = Step::WindowFirst(t.to_string());
@@ -494,6 +512,19 @@ impl CadCommand for DashViewCommand {
                 "-VIEW >WINDOW {}\u{1f}{},{}\u{1f}{},{}",
                 name, first.x, first.y, pt.x, pt.y
             )),
+            Step::RestoreViewport(name) => {
+                // The topmost viewport under the pick.
+                let hit = self.names.sheet_viewports.iter().flatten().rev().find(|(_, [x0, y0, x1, y1])| {
+                    pt.x >= *x0 && pt.x <= *x1 && pt.y >= *y0 && pt.y <= *y1
+                });
+                match hit {
+                    Some((handle, _)) => CmdResult::Dispatch(format!("-VIEW >RESTOREVP {name}\u{1f}{handle:X}")),
+                    None => {
+                        self.step = Step::RestoreViewport(name);
+                        CmdResult::NeedPoint
+                    }
+                }
+            }
             step => {
                 self.step = step;
                 CmdResult::NeedPoint
@@ -503,7 +534,7 @@ impl CadCommand for DashViewCommand {
 
     fn on_enter(&mut self) -> CmdResult {
         match std::mem::replace(&mut self.step, Step::Main) {
-            Step::Main | Step::Delete | Step::Restore | Step::Save | Step::WindowName => {
+            Step::Main | Step::Delete | Step::Restore | Step::RestoreViewport(_) | Step::Save | Step::WindowName => {
                 CmdResult::Dispatch("-VIEW >END".into())
             }
             Step::Orthographic => CmdResult::Dispatch("-VIEW >PRESET TOP".into()),

src/modules/view/visual_style.rs

@@ -106,6 +106,38 @@ pub fn label_for(mode: Mode) -> &'static str {
         .unwrap_or("Wireframe 2D")
 }
 
+/// The render mode a named visual style draws as, and whether the name is a
+/// style of its own (Realistic, Conceptual, …) rather than one of the modes.
+pub fn mode_for_style_name(name: &str) -> Option<(Mode, bool)> {
+    Some(match name {
+        "2dWireframe" => (Mode::Wireframe2D, false),
+        "Wireframe" => (Mode::Wireframe3D, false),
+        "Hidden" => (Mode::HiddenLine, false),
+        "Flat" => (Mode::FlatShaded, false),
+        "FlatWithEdges" => (Mode::FlatShadedWithEdges, false),
+        "Gouraud" => (Mode::GouraudShaded, false),
+        "GouraudWithEdges" => (Mode::GouraudShadedWithEdges, false),
+        "Shaded with edges" => (Mode::GouraudShadedWithEdges, true),
+        "Realistic" | "Shaded" | "Conceptual" | "Shades of Gray" | "Sketchy" | "X-Ray" => {
+            (Mode::GouraudShaded, true)
+        }
+        _ => return None,
+    })
+}
+
+/// The name of the visual style a render mode is saved as.
+pub fn style_name_for(mode: Mode) -> &'static str {
+    match mode {
+        Mode::Wireframe2D => "2dWireframe",
+        Mode::Wireframe3D => "Wireframe",
+        Mode::HiddenLine => "Hidden",
+        Mode::FlatShaded => "Flat",
+        Mode::FlatShadedWithEdges => "FlatWithEdges",
+        Mode::GouraudShaded => "Gouraud",
+        Mode::GouraudShadedWithEdges => "GouraudWithEdges",
+    }
+}
+
 /// The style a style keyword names. Only the seven exist; nothing maps onto a
 /// nearest neighbour, because there is no longer anything else to map from.
 pub fn mode_for_keyword(keyword: &str) -> Option<Mode> {

src/scene/camera_ops.rs

@@ -214,11 +214,28 @@ impl Scene {
 
     /// Restore camera to a named view from the document view table.
     pub fn restore_named_view(&mut self, view: &codec::tables::View) {
-        use glam::Vec3;
-        // The model viewport takes a copy of the view's background, or none.
+        let before = {
+            let cam = self.camera.borrow();
+            (cam.rotation, cam.target, cam.distance)
+        };
+        self.restore_named_view_camera(view);
+        let unchanged = {
+            let cam = self.camera.borrow();
+            cam.rotation.abs_diff_eq(before.0, 1e-6)
+                && cam.target.abs_diff_eq(before.1, 1e-6 * before.1.length().max(1.0))
+                && (cam.distance - before.2).abs() <= 1e-6 * before.2.abs().max(1.0)
+        };
+        // The model viewport takes a copy of the view's background; a view
+        // without one clears it, unless the view is what the viewport already
+        // shows (the reference leaves the viewport as it is then).
+        if self.current_layout != "Model" && self.active_viewport.is_none() && view.paper_space {
+            self.set_sheet_background(view);
+        }
         if self.current_layout == "Model" {
-            let background = copy_background(&mut self.document, view.background_handle);
-            self.set_active_background(background);
+            if view.background_handle.is_valid() || !unchanged {
+                let background = copy_background(&mut self.document, view.background_handle);
+                self.set_active_background(background);
+            }
             if view.visual_style_handle.is_valid() {
                 if let Some(handle) = self.active_tile_vport_handle() {
                     if let Some(value) = self.document.vports.iter_mut().find(|v| v.handle == handle) {
@@ -227,7 +244,50 @@ impl Scene {
                 }
             }
         }
-        let cam = &mut *self.camera.borrow_mut();
+    }
+
+    fn restore_named_view_camera(&mut self, view: &codec::tables::View) {
+        named_view_camera(view, &mut self.camera.borrow_mut());
+        self.camera_generation += 1;
+    }
+
+    /// Restores a model-space view into a paper-space viewport: its camera,
+    /// a copy of the view's background (or none) and the view's visual style.
+    pub fn restore_named_view_in_viewport(&mut self, view: &codec::tables::View, viewport: Handle) {
+        let mut camera = self.navigation_camera();
+        named_view_camera(view, &mut camera);
+        self.apply_navigation_camera(camera);
+        let background = copy_background(&mut self.document, view.background_handle);
+        let mut old = Handle::NULL;
+        if let Some(EntityType::Viewport(value)) = self.document.get_entity_mut(viewport) {
+            old = std::mem::replace(&mut value.background_handle, background);
+            if view.visual_style_handle.is_valid() {
+                value.visual_style_handle = view.visual_style_handle;
+            }
+        }
+        erase_background(&mut self.document, old);
+        self.notify_viewport_changed(viewport);
+        self.camera_generation += 1;
+    }
+
+    /// The paper-space viewport of the current layout takes a copy of a
+    /// paper-space view's background (kept with the layout; the sheet itself
+    /// is not drawn over).
+    fn set_sheet_background(&mut self, view: &codec::tables::View) {
+        let sheet = self.current_layout_sheet_viewport_handle();
+        let background = copy_background(&mut self.document, view.background_handle);
+        let old = match self.document.get_entity_mut(sheet) {
+            Some(EntityType::Viewport(value)) => std::mem::replace(&mut value.background_handle, background),
+            _ => background,
+        };
+        erase_background(&mut self.document, old);
+    }
+}
+
+/// Points a camera along a named view: direction, target and height.
+fn named_view_camera(view: &codec::tables::View, cam: &mut view::camera::Camera) {
+    use glam::Vec3;
+    {
         // The stored direction points from the target toward the eye.
         let eye_dir = Vec3::new(
             view.direction.x as f32,
@@ -254,22 +314,55 @@ impl Scene {
         } else {
             cam.distance
         };
-        self.camera_generation += 1;
     }
+}
 
+impl Scene {
     /// The background the active model-space viewport shows (null for the
     /// drawing area colour).
     pub fn active_background(&self) -> Handle {
+        if self.current_layout != "Model" {
+            // Inside a viewport, that viewport's; the sheet's is not saved
+            // with a paper-space view.
+            return match self.active_viewport.and_then(|handle| self.document.get_entity(handle)) {
+                Some(EntityType::Viewport(value)) => value.background_handle,
+                _ => Handle::NULL,
+            };
+        }
         self.active_tile_vport_handle()
             .and_then(|handle| self.document.vports.iter().find(|value| value.handle == handle))
             .map_or(Handle::NULL, |value| value.background_handle)
     }
 
+    /// The visual style of the active Model tile's viewport record.
+    pub fn active_visual_style(&self) -> Handle {
+        self.active_tile_vport_handle()
+            .and_then(|handle| self.document.vports.iter().find(|value| value.handle == handle))
+            .map_or(Handle::NULL, |value| value.visual_style_handle)
+    }
+
+    /// Records the visual style named `name` on the active Model tile's
+    /// viewport record, when the drawing has it.
+    pub fn set_active_visual_style_named(&mut self, name: &str) {
+        let style = self.document.objects.iter().find_map(|(handle, object)| match object {
+            codec::objects::ObjectType::VisualStyle(style) if style.description == name => Some(*handle),
+            _ => None,
+        });
+        let (Some(style), Some(handle)) = (style, self.active_tile_vport_handle()) else { return };
+        if let Some(value) = self.document.vports.iter_mut().find(|value| value.handle == handle) {
+            value.visual_style_handle = style;
+        }
+    }
+
     fn set_active_background(&mut self, background: Handle) {
         let Some(handle) = self.active_tile_vport_handle() else { return };
-        if let Some(value) = self.document.vports.iter_mut().find(|value| value.handle == handle) {
-            value.background_handle = background;
-            self.camera_generation += 1;
+        let Some(value) = self.document.vports.iter_mut().find(|value| value.handle == handle) else {
+            return;
+        };
+        let old = std::mem::replace(&mut value.background_handle, background);
+        self.camera_generation += 1;
+        if old != background {
+            erase_background(&mut self.document, old);
         }
     }
 
@@ -1713,6 +1806,38 @@ pub fn add_background(
     handle
 }
 
+/// Erases a background object once no view or viewport refers to it (the
+/// reference erases a view's background when it is replaced, cleared or the
+/// view deleted, and a viewport's when the viewport takes another).
+pub fn erase_background(document: &mut codec::CadDocument, handle: Handle) {
+    use codec::objects::{ClassObjectData as D, ObjectType};
+    if !handle.is_valid()
+        || document.views.iter().any(|view| view.background_handle == handle)
+        || document.vports.iter().any(|vport| vport.background_handle == handle)
+        || document.entities().any(|entity| {
+            matches!(entity, codec::EntityType::Viewport(viewport) if viewport.background_handle == handle)
+        })
+    {
+        return;
+    }
+    let owner = match document.objects.get(&handle) {
+        Some(ObjectType::ClassObject(object))
+            if matches!(
+                object.data,
+                D::SolidBackground(_) | D::GradientBackground(_) | D::ImageBackground(_)
+                    | D::GroundPlaneBackground(_) | D::SkyLightBackground(_) | D::IblBackground(_)
+            ) =>
+        {
+            object.owner
+        }
+        _ => return,
+    };
+    document.objects.remove(&handle);
+    if let Some(ObjectType::Dictionary(entries)) = document.objects.get_mut(&owner) {
+        entries.entries.retain(|(_, entry)| *entry != handle);
+    }
+}
+
 /// A copy of a background object (the reference gives each view and
 /// viewport its own); null for none.
 pub fn copy_background(document: &mut codec::CadDocument, handle: Handle) -> Handle {

src/scene/mod.rs

@@ -28,7 +28,7 @@ pub enum BlockScalePolicy {
 // blocks and/or free functions). Pure text-move from the original mod.rs.
 mod boundary;
 mod camera_ops;
-pub use camera_ops::{add_background, copy_background};
+pub use camera_ops::{add_background, copy_background, erase_background};
 pub(crate) mod centerline;
 pub(crate) mod centermark;
 pub(crate) mod dimension_assoc;

src/scene/view/render.rs

@@ -434,8 +434,10 @@ impl shader::Primitive for Primitive {
             // The scene works in logical pixels; an image background keeps
             // its size in device pixels.
             let mut uniforms = vp.uniforms;
-            uniforms.background_image_transform[2] /= scale.max(1e-3);
-            uniforms.background_image_transform[3] /= scale.max(1e-3);
+            // The image's size and offset are in device pixels.
+            for value in &mut uniforms.background_image_transform {
+                *value /= scale.max(1e-3);
+            }
             inner.upload_uniforms(device, queue, &uniforms);
 
             // ── Scene-render cache ────────────────────────────────────────
@@ -2557,20 +2559,18 @@ impl Scene {
         if viewport.paper_sheet {
             let handle = self.current_layout_sheet_viewport_handle();
             if let Some(EntityType::Viewport(value)) = self.document.get_entity(handle) {
-                return build(
-                    value.visual_style_handle,
-                    value.brightness,
-                    value.contrast,
-                    value.background_handle,
-                );
+                // The sheet keeps its page and desk: a paper-space view's
+                // background is kept with the layout but not drawn.
+                return build(value.visual_style_handle, value.brightness, value.contrast, Handle::NULL);
             }
         } else if viewport.handle.is_valid() {
             if let Some(EntityType::Viewport(value)) = self.document.get_entity(viewport.handle) {
+                let flat = value.render_mode == codec::entities::ViewportRenderMode::Wireframe2D;
                 return build(
                     value.visual_style_handle,
                     value.brightness,
                     value.contrast,
-                    value.background_handle,
+                    if flat { Handle::NULL } else { value.background_handle },
                 );
             }
         } else if self.current_layout == "Model" {
@@ -4907,7 +4907,11 @@ impl Scene {
             // (hatched) frame once it settles. Only applied to the on-screen
             // Model / paper content — the paper *sheet* keeps its fills.
             skip_hatch: self.hatch_lod_enabled() && navigating,
-            skip_background: !inst.paper_sheet && self.current_layout != "Model",
+            // A floating viewport shows the page behind it unless it has a
+            // background of its own.
+            skip_background: !inst.paper_sheet
+                && self.current_layout != "Model"
+                && display.background.params[0] < 0.5,
             geometry_epoch: self.geometry_epoch,
             camera_generation: self.camera_generation,
             wire_content_id,

src/shaders/background.wgsl

@@ -81,22 +81,25 @@ fn equirect_uv(ndc: vec2<f32>, rotation: f32) -> vec2<f32> {
 fn image_uv(source_uv: vec2<f32>) -> vec2<f32> {
     var uv = source_uv;
     if u.background_image_params.x < 0.5 {
-        // Not fitted: the image at its own pixel size (times its scale),
-        // centred on the viewport and moved by its offset.
-        let pixel = (source_uv - vec2<f32>(0.5)) * max(u.viewport_size, vec2<f32>(1.0));
-        uv = pixel / max(abs(u.background_image_transform.zw), vec2<f32>(1e-6))
-            + vec2<f32>(0.5) - u.background_image_transform.xy;
+        // Not fitted: the image at its own pixel size times its scale (a
+        // negative scale mirrors it), centred on the viewport and moved by
+        // its offset in pixels, right and down.
+        let pixel = (source_uv - vec2<f32>(0.5)) * max(u.viewport_size, vec2<f32>(1.0))
+            - u.background_image_transform.xy;
+        let size = u.background_image_transform.zw;
+        let safe = select(size, vec2<f32>(1e-6), abs(size) < vec2<f32>(1e-6));
+        uv = pixel / safe + vec2<f32>(0.5);
         return select(uv, fract(uv), u.background_image_params.z > 0.5);
     }
+    // Fitted: the image fills the viewport; keeping its aspect ratio it
+    // covers the viewport and the overflow is cut off evenly.
     if u.background_image_params.y > 0.5 {
         let image_aspect = max(u.background_image_params.w, 1e-6);
         let viewport_aspect = max(u.viewport_size.x / max(u.viewport_size.y, 1.0), 1e-6);
         if image_aspect > viewport_aspect {
-            let scale = viewport_aspect / image_aspect;
-            uv.y = (uv.y - 0.5) / scale + 0.5;
+            uv.x = (uv.x - 0.5) * (viewport_aspect / image_aspect) + 0.5;
         } else {
-            let scale = image_aspect / viewport_aspect;
-            uv.x = (uv.x - 0.5) / scale + 0.5;
+            uv.y = (uv.y - 0.5) * (image_aspect / viewport_aspect) + 0.5;
         }
     }
     if u.background_image_params.z > 0.5 {
@@ -112,28 +115,25 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
     if mode == 1u {
         color = u.viewport_background.rgb;
     } else if mode == 2u {
-        // Bottom to top across the viewport, the "up" direction turned
-        // counter-clockwise by the rotation; in pixels, so the angle holds
-        // whatever the viewport's shape, and spanning corner to corner.
+        // Bottom to top along the "up" direction turned counter-clockwise by
+        // the rotation, in pixels from the viewport centre. As the reference
+        // draws it: the middle colour sits (horizon - 0.5) viewport widths
+        // from the centre and blends linearly into the top and bottom colours
+        // over height viewport heights on each side; two colours are one blend
+        // over a viewport height on each side of the centre.
         let angle = u.background_params.w;
         let up = vec2<f32>(-sin(angle), cos(angle));
         let size = max(u.viewport_size, vec2<f32>(1.0));
         let pixel = (vec2<f32>(in.uv.x, 1.0 - in.uv.y) - vec2<f32>(0.5)) * size;
-        let extent = max(abs(up.x) * size.x + abs(up.y) * size.y, 1.0);
-        let coordinate = clamp(dot(pixel, up) / extent + 0.5, 0.0, 1.0);
-        let horizon = clamp(u.background_params.y, 0.0, 1.0);
-        let half_height = abs(u.background_params.z) * 0.5;
-        if half_height <= 1e-6 {
-            // Two colours: one blend from the bottom to the top, over twice
-            // the viewport (the reference's two-colour gradient reaches the
-            // end colours a viewport beyond the edges).
-            color = mix(u.background_bottom.rgb, u.background_top.rgb, 0.25 + 0.5 * coordinate);
-        } else {
-            let lower = clamp((coordinate - (horizon - half_height)) / half_height, 0.0, 1.0);
-            let upper = clamp((coordinate - horizon) / half_height, 0.0, 1.0);
-            let low_color = mix(u.background_bottom.rgb, u.background_middle.rgb, lower);
-            color = mix(low_color, u.background_top.rgb, upper);
-        }
+        let along = dot(pixel, up);
+        let three = abs(u.background_params.z) > 1e-6;
+        let middle_at = select(0.0, (u.background_params.y - 0.5) * size.x, three);
+        let half_band = select(1.0, abs(u.background_params.z), three) * size.y;
+        let middle = select(mix(u.background_bottom.rgb, u.background_top.rgb, 0.5),
+            u.background_middle.rgb, three);
+        let lower = clamp((along - middle_at + half_band) / half_band, 0.0, 1.0);
+        let upper = clamp((along - middle_at) / half_band, 0.0, 1.0);
+        color = mix(mix(u.background_bottom.rgb, middle, lower), u.background_top.rgb, upper);
     } else if mode == 3u {
         let direction = world_direction(in.ndc);
         if direction.z >= 0.0 {

src/ui/window/pdf_dialogs.rs

@@ -2206,6 +2206,9 @@ pub struct ViewBackgroundState {
     pub image: String,
     pub position: BgPosition,
     pub aspect: bool,
+    /// The image's offset (pixels) and scale, kept from the view's image.
+    pub offset: [f64; 2],
+    pub scale: [f64; 2],
     /// The drawing area colour, shown for no background.
     pub canvas: [u8; 3],
 }