Phase 3: Active viewport MSPACE/PSPACE workflow

- Add active_viewport: Option<Handle> field to Scene
- Add EnterViewport(Handle) and ExitViewport messages
- Double-click on a user viewport (id > 1) enters MSPACE;
  double-click on empty area while in MSPACE exits to PSPACE
- MSPACE middle-drag pans the viewport's model-space view (view_target)
- MSPACE scroll zooms the viewport's view_height / custom_scale
- Drawing commands inside MSPACE receive model-space coordinates
  via paper_to_model() coordinate transform
- Active viewport rendered with yellow dashed border (vs. cyan solid)
- Camera screen_delta_to_world helper for MSPACE pan conversion
- LayoutSwitch clears active_viewport

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/mod.rs

@@ -61,6 +61,10 @@ pub(super) struct H7CAD {
     layout_context_menu: Option<String>,
     /// Inline rename state: (original_name, current_edit_value).
     layout_rename_state: Option<(String, String)>,
+    /// Timestamp of the previous viewport left-click release (for double-click detection).
+    last_vp_click_time: Option<Instant>,
+    /// Screen position of the previous viewport left-click release.
+    last_vp_click_pos: Option<Point>,
 }
 
 #[derive(Debug, Clone)]
@@ -210,6 +214,10 @@ pub enum Message {
     PropColorPickerToggle,
     /// Toggle the full ACI colour palette expansion.
     PropColorPaletteToggle,
+    /// Enter the model-space editing mode inside the given viewport (MSPACE).
+    EnterViewport(acadrust::Handle),
+    /// Exit MSPACE and return to paper-space editing (PSPACE).
+    ExitViewport,
     /// Switch to a named layout ("Model" or paper space layout name).
     LayoutSwitch(String),
     /// Create a new paper space layout.
@@ -261,6 +269,8 @@ impl H7CAD {
             clipboard_centroid: glam::Vec3::ZERO,
             layout_context_menu: None,
             layout_rename_state: None,
+            last_vp_click_time: None,
+            last_vp_click_pos: None,
         };
         app.sync_ribbon_layers();
         app

src/app/update.rs

@@ -6,7 +6,7 @@ use crate::scene::object::GripApply;
 use crate::modules::ModuleEvent;
 use crate::ui::PropertiesPanel;
 use acadrust::types::Color as AcadColor;
-use acadrust::Handle;
+use acadrust::{EntityType as AcadEntityType, Handle};
 use iced::time::Instant;
 use iced::window;
 use iced::{mouse, Task};
@@ -670,10 +670,21 @@ impl H7CAD {
                     }
                 }
 
-                if sel.middle_down {
-                    if let Some(last) = sel.middle_last_pos {
+                let (mid_down, mid_last, vp_size) =
+                    (sel.middle_down, sel.middle_last_pos, sel.vp_size);
+                if mid_down {
+                    if let Some(last) = mid_last {
                         let (dx, dy) = (p.x - last.x, p.y - last.y);
-                        self.tabs[i].scene.camera.borrow_mut().pan(dx, dy);
+                        let bounds = iced::Rectangle { x: 0.0, y: 0.0, width: vp_size.0, height: vp_size.1 };
+                        // Drop `sel` before calling mutable scene methods.
+                        drop(sel);
+                        if self.tabs[i].scene.active_viewport.is_some() {
+                            self.tabs[i].scene.pan_active_viewport(dx, dy, bounds);
+                        } else {
+                            self.tabs[i].scene.camera.borrow_mut().pan(dx, dy);
+                        }
+                        self.tabs[i].scene.selection.borrow_mut().middle_last_pos = Some(p);
+                        return Task::none();
                     }
                     sel.middle_last_pos = Some(p);
                 }
@@ -873,7 +884,9 @@ impl H7CAD {
                     let tangent_obj_at_click = snap_taken.and_then(|s| s.tangent_obj);
 
                     let world_pt = {
-                        let raw = self.tabs[i].scene.camera.borrow().pick_on_target_plane(p, bounds);
+                        let raw_paper = self.tabs[i].scene.camera.borrow().pick_on_target_plane(p, bounds);
+                        // Convert paper-space → model-space when inside a viewport.
+                        let raw = self.tabs[i].scene.paper_to_model(raw_paper);
                         let vp_mat = self.tabs[i].scene.camera.borrow().view_proj(bounds);
                         let all_wires = self.tabs[i].scene.entity_wires();
                         let needs_tan = self.tabs[i].active_cmd.as_ref()
@@ -1059,6 +1072,51 @@ impl H7CAD {
                     }
                 }
 
+                // ── Double-click: enter/exit MSPACE ───────────────────────
+                // Only when no command is running, no drag, and we're in paper space.
+                if is_click
+                    && !is_down2
+                    && self.tabs[i].active_cmd.is_none()
+                    && self.tabs[i].scene.current_layout != "Model"
+                {
+                    let now = Instant::now();
+                    let is_double = self
+                        .last_vp_click_time
+                        .map(|t| {
+                            let dt = now.duration_since(t).as_millis();
+                            let last = self.last_vp_click_pos.unwrap_or(p);
+                            let d = (p.x - last.x).hypot(p.y - last.y);
+                            dt < 400 && d < 8.0
+                        })
+                        .unwrap_or(false);
+
+                    self.last_vp_click_time = Some(now);
+                    self.last_vp_click_pos = Some(p);
+
+                    if is_double {
+                        let (vw, vh) = self.tabs[i].scene.selection.borrow().vp_size;
+                        let bounds = iced::Rectangle { x: 0.0, y: 0.0, width: vw, height: vh };
+                        let vp_mat = self.tabs[i].scene.camera.borrow().view_proj(bounds);
+                        let all_wires = self.tabs[i].scene.entity_wires();
+                        let hit = scene::hit_test::click_hit(p, &all_wires, vp_mat, bounds)
+                            .and_then(|s| Scene::handle_from_wire_name(s));
+
+                        if let Some(handle) = hit {
+                            // Double-clicked on a user viewport → enter MSPACE.
+                            if let Some(AcadEntityType::Viewport(vp)) =
+                                self.tabs[i].scene.document.get_entity(handle)
+                            {
+                                if vp.id > 1 {
+                                    return Task::done(Message::EnterViewport(handle));
+                                }
+                            }
+                        } else if self.tabs[i].scene.active_viewport.is_some() {
+                            // Double-clicked on empty area while in MSPACE → exit.
+                            return Task::done(Message::ExitViewport);
+                        }
+                    }
+                }
+
                 Task::none()
             }
 
@@ -1130,11 +1188,16 @@ impl H7CAD {
                 let cursor = self.tabs[i].scene.selection.borrow().last_move_pos;
                 let (vw, vh) = self.tabs[i].scene.selection.borrow().vp_size;
                 let bounds = iced::Rectangle { x: 0.0, y: 0.0, width: vw, height: vh };
-                let mut cam = self.tabs[i].scene.camera.borrow_mut();
-                if let Some(cursor) = cursor {
-                    cam.zoom_about_point(cursor, bounds, s);
+                if self.tabs[i].scene.active_viewport.is_some() {
+                    // In MSPACE: zoom the active viewport's model-space view.
+                    self.tabs[i].scene.zoom_active_viewport(s);
                 } else {
-                    cam.zoom(s);
+                    let mut cam = self.tabs[i].scene.camera.borrow_mut();
+                    if let Some(cursor) = cursor {
+                        cam.zoom_about_point(cursor, bounds, s);
+                    } else {
+                        cam.zoom(s);
+                    }
                 }
                 Task::none()
             }
@@ -1431,9 +1494,10 @@ impl H7CAD {
             Message::LayoutSwitch(name) => {
                 let i = self.active_tab;
                 let going_to_paper = name != "Model";
-                // Cancel any pending rename/context-menu when switching layouts.
+                // Cancel any pending rename/context-menu and active viewport when switching.
                 self.layout_rename_state = None;
                 self.layout_context_menu = None;
+                self.tabs[i].scene.active_viewport = None;
                 self.tabs[i].scene.current_layout = name;
                 self.tabs[i].scene.deselect_all();
                 self.tabs[i].scene.fit_all();
@@ -1559,6 +1623,20 @@ impl H7CAD {
                 Task::none()
             }
 
+            Message::EnterViewport(handle) => {
+                let i = self.active_tab;
+                self.tabs[i].scene.active_viewport = Some(handle);
+                self.command_line.push_output("MSPACE — viewport entered. Middle-drag/scroll to navigate, double-click outside to exit.");
+                Task::none()
+            }
+
+            Message::ExitViewport => {
+                let i = self.active_tab;
+                self.tabs[i].scene.active_viewport = None;
+                self.command_line.push_output("PSPACE");
+                Task::none()
+            }
+
             Message::Undo => { self.undo_active_tab(); Task::none() }
             Message::Redo => { self.redo_active_tab(); Task::none() }
 

src/scene/camera.rs

@@ -201,6 +201,16 @@ impl Camera {
         self.target += cam_up * delta_y * speed;
     }
 
+    /// Returns the world-space translation that `pan(delta_x, delta_y)` would
+    /// apply to the camera target — without actually moving the camera.
+    /// Used by MSPACE to pan the viewport's model-space view independently.
+    pub fn screen_delta_to_world(&self, delta_x: f32, delta_y: f32, _bounds: Rectangle) -> Vec3 {
+        let speed = self.distance * 0.001;
+        let cam_right = self.rotation * Vec3::X;
+        let cam_up = self.rotation * Vec3::Y;
+        -(cam_right * delta_x * speed) + (cam_up * delta_y * speed)
+    }
+
     pub fn fit_to_bounds(&mut self, min: Vec3, max: Vec3) {
         self.target = (min + max) * 0.5;
         let size = (max - min).length();

src/scene/mod.rs

@@ -61,6 +61,10 @@ pub struct Scene {
     pub hatches: HashMap<Handle, HatchModel>,
     /// GPU render data for solid meshes (truck Shell/Solid tessellation).
     pub meshes: HashMap<Handle, MeshModel>,
+    /// The viewport that is currently "entered" (MSPACE mode).
+    /// `None` = paper space editing (PSPACE).  Only meaningful when
+    /// `current_layout != "Model"`.
+    pub active_viewport: Option<Handle>,
 }
 
 impl Scene {
@@ -76,6 +80,7 @@ impl Scene {
             current_layout: "Model".to_string(),
             hatches: HashMap::new(),
             meshes: HashMap::new(),
+            active_viewport: None,
         }
     }
 
@@ -255,20 +260,32 @@ impl Scene {
         let sel = self.selected.contains(&h);
 
         if let EntityType::Viewport(vp) = e {
+            let is_active = self.active_viewport == Some(h);
             let color = if vp.id == 1 {
+                // Overall paper-space viewport — subtle grey.
                 [0.40, 0.40, 0.40, 1.0]
+            } else if is_active {
+                // Active (entered) viewport — bright yellow.
+                [1.0, 0.90, 0.20, 1.0]
             } else {
+                // Normal user viewport — cyan.
                 [0.0, 0.75, 0.75, 1.0]
             };
+            // Active viewport gets a dashed border to visually indicate MSPACE.
+            let (pattern_length, pattern) = if is_active {
+                (1.5_f32, [0.8, -0.4, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0_f32])
+            } else {
+                (0.0_f32, [0.0f32; 8])
+            };
             return vec![tessellate::tessellate(
                 &self.document,
                 h,
                 e,
                 sel,
                 color,
-                0.0,
-                [0.0f32; 8],
-                1.0,
+                pattern_length,
+                pattern,
+                1.5,
             )];
         }
 
@@ -441,6 +458,93 @@ impl Scene {
         result
     }
 
+    // ── MSPACE helpers ───────────────────────────────────────────────────
+
+    /// Convert a **paper-space** world coordinate to **model-space** using the
+    /// geometry of the currently active viewport.  Returns the input unchanged
+    /// when there is no active viewport.
+    pub fn paper_to_model(&self, paper_pt: glam::Vec3) -> glam::Vec3 {
+        let vp_handle = match self.active_viewport {
+            Some(h) => h,
+            None => return paper_pt,
+        };
+        let vp = match self.document.get_entity(vp_handle) {
+            Some(acadrust::EntityType::Viewport(vp)) => vp,
+            _ => return paper_pt,
+        };
+        let scale = if vp.custom_scale.abs() > 1e-9 {
+            vp.custom_scale as f32
+        } else if vp.view_height.abs() > 1e-9 {
+            (vp.height / vp.view_height) as f32
+        } else {
+            1.0
+        };
+        if scale.abs() < 1e-9 {
+            return paper_pt;
+        }
+        let tx = vp.view_target.x as f32;
+        let ty = vp.view_target.y as f32;
+        let pcx = vp.center.x as f32;
+        let pcy = vp.center.y as f32;
+        glam::Vec3::new(
+            (paper_pt.x - pcx) / scale + tx,
+            (paper_pt.y - pcy) / scale + ty,
+            paper_pt.z,
+        )
+    }
+
+    /// Pan the active viewport's model-space view by `(screen_dx, screen_dy)` pixels.
+    /// The delta is converted to model-space units using the camera and viewport scale.
+    /// No-op when there is no active viewport.
+    pub fn pan_active_viewport(&mut self, screen_dx: f32, screen_dy: f32, bounds: iced::Rectangle) {
+        let vp_handle = match self.active_viewport {
+            Some(h) => h,
+            None => return,
+        };
+        // Convert screen pixels → paper-space delta using the camera.
+        let cam = self.camera.borrow();
+        let paper_delta = cam.screen_delta_to_world(screen_dx, screen_dy, bounds);
+        drop(cam);
+
+        if let Some(acadrust::EntityType::Viewport(vp)) =
+            self.document.get_entity_mut(vp_handle)
+        {
+            let scale = if vp.custom_scale.abs() > 1e-9 {
+                vp.custom_scale
+            } else if vp.view_height.abs() > 1e-9 {
+                vp.height / vp.view_height
+            } else {
+                1.0
+            };
+            if scale.abs() < 1e-12 { return; }
+            // Paper delta → model delta (divide by viewport scale).
+            vp.view_target.x -= (paper_delta.x / scale as f32) as f64;
+            vp.view_target.y -= (paper_delta.y / scale as f32) as f64;
+        }
+    }
+
+    /// Zoom the active viewport's model-space view by `steps` notches.
+    /// Positive = zoom in (increase detail), negative = zoom out.
+    /// No-op when there is no active viewport.
+    pub fn zoom_active_viewport(&mut self, steps: f32) {
+        let vp_handle = match self.active_viewport {
+            Some(h) => h,
+            None => return,
+        };
+        if let Some(acadrust::EntityType::Viewport(vp)) =
+            self.document.get_entity_mut(vp_handle)
+        {
+            // Zoom in = shrink view_height → more of the model fits less area.
+            let factor = (1.0_f64 - 0.15 * steps as f64).clamp(0.1, 10.0);
+            let new_height = (vp.view_height * factor).max(1e-6);
+            vp.view_height = new_height;
+            // Keep custom_scale in sync.
+            if vp.view_height.abs() > 1e-9 {
+                vp.custom_scale = vp.height / vp.view_height;
+            }
+        }
+    }
+
     // ── Layout management ─────────────────────────────────────────────────
 
     /// Rename a paper-space layout.  Updates the Layout object name in the document.