Add Sticky Zoom to keep zoom level across image switches

docs/USER_GUIDE.md

@@ -11,7 +11,7 @@ This guide is for new users. It explains what each control does, when you'd reac
 ### Screen layout
 
 *   **Left, the film strip**: your loaded frames as a contact sheet, plus import, sorting, and triage tools.
-*   **Centre, the canvas**: the live preview of the current frame. Most tools (crop, white-balance picker, heal brush, dodge/burn masks) are used by clicking directly on it. A floating toolbar along the bottom holds Fit/1:1 zoom, undo/redo, rotate/flip and more, moving overflow items into an **⋯** menu when the window narrows — that menu also has **Immersive Canvas** (image fills the canvas and the toolbar overlaps it; turn off to reserve space above the toolbar so it never occludes the image). With nothing loaded it shows **Load some scans to get started** — click it for **Add files** / **Add folder**.
+*   **Centre, the canvas**: the live preview of the current frame. Most tools (crop, white-balance picker, heal brush, dodge/burn masks) are used by clicking directly on it. Scroll/pinch to zoom and drag to pan; a floating toolbar along the bottom holds Fit/1:1 zoom plus undo/redo, rotate/flip and more, moving overflow items into an **⋯** menu when the window narrows — that menu also has **Immersive Canvas** (image fills the canvas and the toolbar overlaps it; turn off to reserve space so it never occludes the image). Right-click the image for **Reset View** and **Sticky Zoom** (keeps the current zoom level when you switch to another frame, instead of resetting to fit), alongside the picker tools and copy/paste settings. With nothing loaded it shows **Load some scans to get started** — click it for **Add files** / **Add folder**.
 *   **Right, the controls**: a pinned **Analysis** readout at the top, and below it an icon tab bar. Each icon opens a *workflow page* holding one or more collapsible panels.
 
 ### The workflow (and the order things happen)

negpy/desktop/controller.py

@@ -631,7 +631,7 @@ def _connect_signals(self) -> None:
         self.session.active_file_changing.connect(lambda: self._update_thumbnail_from_state(force_readback=True))
         self.session.session_emptied.connect(self._render_memo.clear)
         self.session.session_emptied.connect(self._strip_memo.clear)
-        self.session.file_selected.connect(self.load_file)
+        self.session.file_selected.connect(self._on_file_selected_load)
         self.session.state_changed.connect(self.config_updated.emit)
         self.session.state_changed.connect(self._render_debounce.start)
         self.session.files_changed.connect(self._render_debounce.start)
@@ -1220,6 +1220,10 @@ def _strip_memo_key(self, kind: str = "tone") -> str:
             exposure = replace(exposure, density=1.0, grade=115.0)
         return f"{kind}:{self._render_memo_key(replace(self.state.config, exposure=exposure))}"
 
+    def _on_file_selected_load(self, file_path: str) -> None:
+        """``session.file_selected`` handler: navigation honors the sticky-zoom preference."""
+        self.load_file(file_path, preserve_zoom=self.state.sticky_zoom)
+
     def load_file(self, file_path: str, preserve_zoom: bool = False, force_detect: bool = False) -> None:
         """
         Dispatches RAW decode to a background worker to keep the UI thread free.

negpy/desktop/session.py

@@ -100,6 +100,10 @@ class AppState:
     # canvas and the toolbar overlaps.
     immersive_canvas: bool = True
 
+    # When True, switching to a different image keeps the current zoom level
+    # instead of resetting to fit-to-window.
+    sticky_zoom: bool = False
+
     # Crop tool composition guide (CropGuide value); display-only, so not in GeometryConfig
     crop_guide: str = "thirds"
     crop_guide_orientation: int = 0
@@ -472,6 +476,10 @@ def __init__(self, repo: StorageRepository):
         if saved_immersive is not None:
             self.state.immersive_canvas = bool(saved_immersive)
 
+        saved_sticky_zoom = self.repo.get_global_setting("sticky_zoom")
+        if saved_sticky_zoom is not None:
+            self.state.sticky_zoom = bool(saved_sticky_zoom)
+
         saved_guide = self.repo.get_global_setting("crop_guide")
         if saved_guide in set(CropGuide):
             self.state.crop_guide = str(saved_guide)
@@ -574,6 +582,13 @@ def set_immersive_canvas(self, enabled: bool) -> None:
             self.repo.save_global_setting("immersive_canvas", enabled)
             self.state_changed.emit()
 
+    def set_sticky_zoom(self, enabled: bool) -> None:
+        """Updates and persists whether zoom carries over between images."""
+        if self.state.sticky_zoom != enabled:
+            self.state.sticky_zoom = enabled
+            self.repo.save_global_setting("sticky_zoom", enabled)
+            self.state_changed.emit()
+
     def set_canvas_bg(self, index: int) -> None:
         """Updates and persists the canvas background color index."""
         if self.state.canvas_bg_index != index:

negpy/desktop/view/canvas/toolbar.py

@@ -327,6 +327,12 @@ def _init_ui(self) -> None:
         self._ov_immersive_action.setToolTip(
             tooltip_with_shortcut("Toolbar overlaps image — turn off to fit the image above the toolbar", "toggle_immersive_canvas")
         )
+        self._ov_sticky_zoom_action = overflow_menu.addAction("Sticky Zoom")
+        self._ov_sticky_zoom_action.setCheckable(True)
+        self._ov_sticky_zoom_action.setChecked(self.session.state.sticky_zoom)
+        self._ov_sticky_zoom_action.setToolTip(
+            tooltip_with_shortcut("Keep the current zoom level when switching images, instead of resetting to fit", "toggle_sticky_zoom")
+        )
         overflow_menu.addSeparator()
 
         db_action = overflow_menu.addAction(qta.icon("fa5s.database", color=icon_color), "Manage Database…", self._show_database_dialog)
@@ -484,6 +490,7 @@ def _connect_signals(self) -> None:
         self._ov_undo_action.triggered.connect(lambda: _context_undo(self.controller))
         self._ov_redo_action.triggered.connect(self.session.redo)
         self._ov_immersive_action.triggered.connect(self._on_immersive_toggled)
+        self._ov_sticky_zoom_action.triggered.connect(self._on_sticky_zoom_toggled)
 
     def _on_overflow_unload(self) -> None:
         from negpy.desktop.view.confirm import confirm_unload
@@ -496,6 +503,9 @@ def _on_overflow_unload(self) -> None:
     def _on_immersive_toggled(self, checked: bool) -> None:
         self.session.set_immersive_canvas(checked)
 
+    def _on_sticky_zoom_toggled(self, checked: bool) -> None:
+        self.session.set_sticky_zoom(checked)
+
     def _on_gpu_toggled(self, checked: bool) -> None:
         if checked != self.session.state.gpu_enabled:
             self.session.set_gpu_enabled(checked)
@@ -655,6 +665,7 @@ def _update_ui_state(self) -> None:
         self._ov_flip_h_action.setChecked(geo.flip_horizontal)
         self._ov_flip_v_action.setChecked(geo.flip_vertical)
         self._ov_immersive_action.setChecked(state.immersive_canvas)
+        self._ov_sticky_zoom_action.setChecked(state.sticky_zoom)
 
         self.btn_undo.setEnabled(state.undo_index > 0)
         self.btn_redo.setEnabled(state.undo_index < state.max_history_index)

negpy/desktop/view/canvas/widget.py

@@ -609,6 +609,10 @@ def contextMenuEvent(self, event) -> None:
         menu.addSeparator()
         act_reset = menu.addAction("Reset View")
         act_reset.triggered.connect(self.fit_to_window)
+        act_sticky_zoom = menu.addAction("Sticky Zoom")
+        act_sticky_zoom.setCheckable(True)
+        act_sticky_zoom.setChecked(self.state.sticky_zoom)
+        act_sticky_zoom.toggled.connect(self._controller.session.set_sticky_zoom)  # type: ignore[union-attr]
         menu.exec(event.globalPos())
 
     def _exec_retouch_menu(self, event) -> None:

negpy/desktop/view/keyboard_shortcuts.py

@@ -120,6 +120,7 @@ def _build_actions(self) -> dict[str, Callable[[], None]]:
             "search_library": self.window.session_panel.file_browser.search_library,
             "toggle_library_tree": self.window.session_panel.toggle_library_tree,
             "toggle_immersive_canvas": lambda: controller.session.set_immersive_canvas(not controller.session.state.immersive_canvas),
+            "toggle_sticky_zoom": lambda: controller.session.set_sticky_zoom(not controller.session.state.sticky_zoom),
             "toggle_left_panel": self.window.toggle_session_dock,
             "toggle_right_panel": self.window.toggle_controls_dock,
             "reset_panel_layout": self.window.reset_panel_layout,

negpy/desktop/view/shortcut_registry.py

@@ -137,6 +137,7 @@ class ShortcutEntry:
     "search_library": ShortcutEntry("Ctrl+Shift+F", "Search every library folder and load the matches", "Navigation"),
     "toggle_library_tree": ShortcutEntry("", "Show/hide the library folder tree", "View"),
     "toggle_immersive_canvas": ShortcutEntry("", "Immersive canvas (toolbar overlaps image)", "View"),
+    "toggle_sticky_zoom": ShortcutEntry("", "Sticky zoom (keep zoom level when switching images)", "View"),
     "toggle_left_panel": ShortcutEntry("Ctrl+[", "Toggle session panel (re-docks when floating)", "View"),
     "toggle_right_panel": ShortcutEntry("Ctrl+]", "Toggle controls panel (re-docks when floating)", "View"),
     "reset_panel_layout": ShortcutEntry("Ctrl+Shift+L", "Dock session and controls panels", "View"),

tests/test_controller.py

@@ -409,6 +409,26 @@ def test_load_file_preserve_zoom(self):
 
         mock_slot.assert_not_called()
 
+    def test_file_selected_navigation_resets_zoom_by_default(self):
+        """Switching images via session.file_selected resets zoom unless sticky_zoom is on."""
+        self.controller.state.sticky_zoom = False
+        mock_slot = MagicMock()
+        self.controller.zoom_requested.connect(mock_slot)
+
+        self.controller._on_file_selected_load("dummy.dng")
+
+        mock_slot.assert_called_once_with(1.0)
+
+    def test_file_selected_navigation_preserves_zoom_when_sticky(self):
+        """With sticky_zoom on, switching images must not reset the zoom level."""
+        self.controller.state.sticky_zoom = True
+        mock_slot = MagicMock()
+        self.controller.zoom_requested.connect(mock_slot)
+
+        self.controller._on_file_selected_load("dummy.dng")
+
+        mock_slot.assert_not_called()
+
     def test_toggle_hq_preview_preserves_zoom(self):
         """Test that toggling HQ mode persists via session and preserves zoom."""
         self.controller.state.current_file_path = "dummy.dng"

tests/test_desktop_session.py

@@ -161,6 +161,16 @@ def test_set_autodetect_enabled_noop_when_unchanged(self):
         self.session.set_autodetect_enabled(False)
         self.mock_repo.save_global_setting.assert_not_called()
 
+    def test_set_sticky_zoom_persists(self):
+        self.assertFalse(self.session.state.sticky_zoom)
+        self.session.set_sticky_zoom(True)
+        self.assertTrue(self.session.state.sticky_zoom)
+        self.mock_repo.save_global_setting.assert_called_with("sticky_zoom", True)
+
+    def test_set_sticky_zoom_noop_when_unchanged(self):
+        self.session.set_sticky_zoom(False)
+        self.mock_repo.save_global_setting.assert_not_called()
+
     def test_persist_writes_sticky_settings_in_one_batch(self):
         self.session.select_file(0)
         self.mock_repo.save_global_settings.reset_mock()