feat(history): compare the edit with any history step or work print

docs/USER_GUIDE.md

@@ -77,7 +77,7 @@ A new frame gets the roll's film type, and the crop, print stock and Lab setting
 
 ### Viewing
 
-*   **Before / After** (`\`, or the **Print** menu): splits the canvas between the default conversion and your edit. Hold `\` to see the default alone.
+*   **Before / After** (`\`, or the **Print** menu): splits the canvas between the default conversion and your edit. Hold `\` to see the default alone. To compare with an earlier version, right-click it in **History**.
 *   **Peeks**: hold `N` for the scan as loaded (the negative), `M` for the flat master, and `P` for the camera's own JPEG. The **Print** menu has them too.
 *   **Reference View** (`Shift+R`): pins this frame beside the canvas, to match other frames to it.
 *   **Probe at Cursor** (`Shift+I`, **Overlays** menu): shows the density and zone under the pointer.
@@ -441,13 +441,13 @@ A **work print** is a version of this frame that you keep under a name, like the
 
 *   **Save Work Print…** (`Ctrl+Shift+S`) keeps the current edit.
 *   **Click** a work print to use it. `Ctrl+Z` goes back.
-*   **⋮** or right-click: **Export This Version…**, **Rename…** or **Delete…**.
+*   **⋮** or right-click: **Compare With This Version**, **Export This Version…**, **Rename…** or **Delete…**. **Compare With This Version** opens **Before / After** with the work print on the left.
 *   **Load Metadata** (off at first): also restores the metadata saved with the work print.
 
 <!-- panel:edit_history -->
 ### Edit history
 
-Every change you made, newest on top (the last 100). **Now** marks the current state; after an undo, later steps show as **Undone** until your next edit. Click a step to go back to it. **⋮** or right-click → **Export This Version…** exports a past state.
+Every change you made, newest on top (the last 100). **Now** marks the current state; after an undo, later steps show as **Undone** until your next edit. Click a step to go back to it. **⋮** or right-click → **Export This Version…** exports a past state. **Compare With This Step** opens **Before / After** with that step on the left, on your current crop. Press `\` to close it.
 
 ---
 

negpy/desktop/controller.py

@@ -412,6 +412,24 @@ def baseline_compare_config(config: WorkspaceConfig) -> WorkspaceConfig:
     )
 
 
+def reference_compare_config(reference: WorkspaceConfig, config: WorkspaceConfig) -> WorkspaceConfig:
+    """
+    The 'before' config for a split against a history step or work print: its look on the
+    current framing, composite, flat field and output settings, so both halves line up.
+    The preview source is not decoded again, so a step's other source settings take no effect.
+    """
+    return replace(
+        reference,
+        geometry=config.geometry,
+        stitch=config.stitch,
+        hdr=config.hdr,
+        flatfield=config.flatfield,
+        rgbscan=config.rgbscan,
+        metadata=config.metadata,
+        export=config.export,
+    )
+
+
 # Solved knee fields under their slider names (sidebar/tone.py).
 _KNEE_LABELS = {
     "shadow_grade": tr("Shadows Grade"),
@@ -7369,6 +7387,9 @@ def request_render(
         self.render_requested.emit(task)
 
     def _baseline_compare_config(self) -> WorkspaceConfig:
+        reference = self.state.compare_reference
+        if reference is not None:
+            return reference_compare_config(reference, self.state.config)
         return baseline_compare_config(self.state.config)
 
     def _compare_before_key(self) -> str:
@@ -7404,10 +7425,42 @@ def exit_compare(self) -> None:
         self.state.compare_before = None
         self.state.compare_before_rect = None
         self.state.compare_before_key = ""
+        self.state.compare_reference = None
+        self.state.compare_reference_label = ""
         if self.state.compare_mode:
             self.state.compare_mode = False
             self.compare_changed.emit(False)
 
+    def compare_with_history_step(self, index: int) -> None:
+        """Open the split against a history step instead of the default conversion."""
+        file_hash = self.state.current_file_hash
+        if not file_hash:
+            return
+        # The live top step may not be persisted yet: it lives in state.config.
+        config = self.state.config if index == self.state.undo_index else self.session.repo.load_history_step(file_hash, index)
+        self._compare_with(config, tr("STEP {number}", number=index))
+
+    def compare_with_work_print(self, name: str) -> None:
+        """Open the split against a work print instead of the default conversion."""
+        file_hash = self.state.current_file_hash
+        if not file_hash:
+            return
+        self._compare_with(self.session.repo.load_work_print(file_hash, name), name.upper())
+
+    def _compare_with(self, config: Optional[WorkspaceConfig], label: str) -> None:
+        if config is None or self.state.preview_raw is None:
+            return
+        self.state.compare_reference = config
+        self.state.compare_reference_label = label
+        if not self.state.compare_mode:
+            self.toggle_compare()
+            return
+        # Drop the old reference's pixels, or they show under the new badge until the render lands.
+        self.state.compare_before = None
+        self.state.compare_before_key = ""
+        self.compare_frame_ready.emit()
+        self._request_compare_baseline()
+
     def begin_compare_hold(self) -> None:
         """Show the baseline over the whole picture until end_compare_hold. Only over the print:
         a peek, the test strip or an uncropped tool view has no baseline that lines up."""
@@ -7434,7 +7487,8 @@ def end_compare_hold(self) -> None:
             self.compare_hold_changed.emit(False)
 
     def toggle_compare(self) -> None:
-        """Toggle the before/after split between the edit and the auto baseline."""
+        """Toggle the before/after split between the edit and the auto baseline, or the
+        history step or work print set by _compare_with."""
         if self.state.preview_raw is None:
             return
         if self.state.compare_mode:

negpy/desktop/session.py

@@ -328,6 +328,10 @@ class AppState:
     compare_split: float = 0.5
     # True while the compare key is held: the whole picture shows the baseline.
     compare_hold: bool = False
+    # A history step or work print the split compares against instead of the default
+    # conversion, and its badge text. Held as a config: a later edit can delete the step.
+    compare_reference: Optional[Any] = None
+    compare_reference_label: str = ""
 
     # Export presets (globally managed, not per-file)
     export_presets: List[ExportPreset] = field(default_factory=list)

negpy/desktop/view/canvas/overlay.py

@@ -1396,8 +1396,9 @@ def _draw_compare_split(self, painter: QPainter) -> None:
         knob = QRectF(centre.x() - _SPLIT_HANDLE_PX, centre.y() - _SPLIT_HANDLE_PX, 2 * _SPLIT_HANDLE_PX, 2 * _SPLIT_HANDLE_PX)
         painter.drawText(knob, Qt.AlignmentFlag.AlignCenter, "◂▸")
 
-        if x - target.left() > 92:
-            draw_view_badge(painter, tr("BEFORE"), target.left() + THEME.space_xl, target.top() + THEME.space_xl)
+        before_text = self.state.compare_reference_label or tr("BEFORE")
+        if x - target.left() > max(92.0, view_badge_width(painter, before_text) + 2 * THEME.space_xl):
+            draw_view_badge(painter, before_text, target.left() + THEME.space_xl, target.top() + THEME.space_xl)
         if target.right() - x > 92:
             after = tr("AFTER")
             draw_view_badge(

negpy/desktop/view/sidebar/history.py

@@ -218,21 +218,29 @@ def _on_context_menu(self, pos) -> None:
         if item is None:
             return
         menu = QMenu(self)
+        # The current step is the After half, so comparing against it shows nothing.
+        compare_action = None if item.data(_TAG_ROLE) == "now" else menu.addAction(tr("Compare With This Step"))
         export_action = menu.addAction(tr("Export This Version…"))
-        if menu.exec(self.list.mapToGlobal(pos)) is export_action:
+        chosen = menu.exec(self.list.mapToGlobal(pos))
+        if chosen is export_action:
             self.controller.export_history_step(item.data(_INDEX_ROLE))
+        elif chosen is not None and chosen is compare_action:
+            self.controller.compare_with_history_step(item.data(_INDEX_ROLE))
 
     def _on_work_print_menu(self, pos) -> None:
         item = self.work_prints.itemAt(pos)
         if item is None:
             return
         name = item.text()
         menu = QMenu(self)
+        compare_action = menu.addAction(tr("Compare With This Version"))
         export_action = menu.addAction(tr("Export This Version…"))
         rename_action = menu.addAction(tr("Rename…"))
         delete_action = menu.addAction(tr("Delete…"))
         chosen = menu.exec(self.work_prints.mapToGlobal(pos))
-        if chosen is export_action:
+        if chosen is compare_action:
+            self.controller.compare_with_work_print(name)
+        elif chosen is export_action:
             self.controller.export_work_print(name)
         elif chosen is rename_action:
             new_name, ok = QInputDialog.getText(self, tr("Rename Work Print"), tr("Name:"), text=name)

negpy/translations/USER_GUIDE.en.md

@@ -77,7 +77,7 @@ A new frame gets the roll's film type, and the crop, print stock and Lab setting
 
 ### Viewing
 
-*   **Before / After** (`\`, or the **Print** menu): splits the canvas between the default conversion and your edit. Hold `\` to see the default alone.
+*   **Before / After** (`\`, or the **Print** menu): splits the canvas between the default conversion and your edit. Hold `\` to see the default alone. To compare with an earlier version, right-click it in **History**.
 *   **Peeks**: hold `N` for the scan as loaded (the negative), `M` for the flat master, and `P` for the camera's own JPEG. The **Print** menu has them too.
 *   **Reference View** (`Shift+R`): pins this frame beside the canvas, to match other frames to it.
 *   **Probe at Cursor** (`Shift+I`, **Overlays** menu): shows the density and zone under the pointer.
@@ -441,13 +441,13 @@ A **work print** is a version of this frame that you keep under a name, like the
 
 *   **Save Work Print…** (`Ctrl+Shift+S`) keeps the current edit.
 *   **Click** a work print to use it. `Ctrl+Z` goes back.
-*   **⋮** or right-click: **Export This Version…**, **Rename…** or **Delete…**.
+*   **⋮** or right-click: **Compare With This Version**, **Export This Version…**, **Rename…** or **Delete…**. **Compare With This Version** opens **Before / After** with the work print on the left.
 *   **Load Metadata** (off at first): also restores the metadata saved with the work print.
 
 <!-- panel:edit_history -->
 ### Edit history
 
-Every change you made, newest on top (the last 100). **Now** marks the current state; after an undo, later steps show as **Undone** until your next edit. Click a step to go back to it. **⋮** or right-click → **Export This Version…** exports a past state.
+Every change you made, newest on top (the last 100). **Now** marks the current state; after an undo, later steps show as **Undone** until your next edit. Click a step to go back to it. **⋮** or right-click → **Export This Version…** exports a past state. **Compare With This Step** opens **Before / After** with that step on the left, on your current crop. Press `\` to close it.
 
 ---
 

negpy/translations/USER_GUIDE.ja.md

@@ -285,20 +285,20 @@ NegPy は、フィルムスキャンをポジ画像に仕上げる仮想暗室
 - **保存…**：現在の設定のうちどれを新しいプリセットにするかを選びます。プリセットにはトリミングと光学補正の設定をフラットフィールドのプロファイルと共に保存できますが、フレームごとのトリミング、回転、反転は保存しません。
 - **ペン**と**ゴミ箱**：選択したプリセットを編集または削除します。
 
-<!-- panel:work_prints src:e8bf683e -->
+<!-- panel:work_prints src:6d4f4720 -->
 ## ワークプリント
 
 **ワークプリント**は、名前を付けて残すこのフレームのバージョンです。仕上げまでに作るテストプリントと同じです。
 
 - **ワークプリントを保存…**（`Ctrl+Shift+S`）で現在の編集を残します。
 - ワークプリントを**クリック**すると使います。`Ctrl+Z` で戻ります。
-- **⋮** または右クリック：**このバージョンをエクスポート…**、**名前を変更…**、**削除…**。
+- **⋮** または右クリック：**このバージョンと比較**、**このバージョンをエクスポート…**、**名前を変更…**、**削除…**。**このバージョンと比較**は、ワークプリントを左側にして**ビフォー / アフター**を開きます。
 - **メタデータのロード**（最初はオフ）：ワークプリントと一緒に保存したメタデータも戻します。
 
-<!-- panel:edit_history src:57abcbf1 -->
+<!-- panel:edit_history src:59f9ee38 -->
 ## 編集履歴
 
-行ったすべての変更を新しい順に表示します（最新 100 件）。**現在**が今の状態です。元に戻した後は、次に編集するまで後の手順が**取り消し済み**になります。手順をクリックするとその状態に戻ります。**⋮** または右クリック →**このバージョンをエクスポート…**で過去の状態を書き出します。
+行ったすべての変更を新しい順に表示します（最新 100 件）。**現在**が今の状態です。元に戻した後は、次に編集するまで後の手順が**取り消し済み**になります。手順をクリックするとその状態に戻ります。**⋮** または右クリック →**このバージョンをエクスポート…**で過去の状態を書き出します。**このステップと比較**は、そのステップを左側にして、現在のトリミングで**ビフォー / アフター**を開きます。`\` で閉じます。
 
 <!-- panel:film src:7e289624 -->
 ## セットアップ

negpy/translations/USER_GUIDE.ko.md

@@ -285,20 +285,20 @@ NegPy는 필름 스캔을 포지티브 이미지로 만드는 가상 암실입
 - **저장…**: 현재 설정 중 무엇을 새 사전 설정으로 저장할지 고릅니다. 사전 설정에는 자르기와 광학 보정 설정을 플랫 필드 프로필과 함께 저장할 수 있지만, 프레임별 자르기, 회전, 뒤집기는 저장하지 않습니다.
 - **펜**과 **휴지통**: 선택한 사전 설정을 편집하거나 삭제합니다.
 
-<!-- panel:work_prints src:e8bf683e -->
+<!-- panel:work_prints src:6d4f4720 -->
 ## 작업 인화물
 
 **작업 인화**는 이름을 붙여 보관하는 이 프레임의 버전으로, 최종 인화까지 만드는 테스트 인화와 같습니다.
 
 - **작업 인화 저장…**(`Ctrl+Shift+S`)으로 현재 편집을 보관합니다.
 - 작업 인화를 **클릭**하면 사용합니다. `Ctrl+Z`로 되돌립니다.
-- **⋮** 또는 오른쪽 클릭: **이 버전 내보내기…**, **이름 바꾸기…**, **삭제…**.
+- **⋮** 또는 오른쪽 클릭: **이 버전과 비교**, **이 버전 내보내기…**, **이름 바꾸기…**, **삭제…**. **이 버전과 비교**는 작업 인화를 왼쪽에 두고 **전/후**를 엽니다.
 - **메타데이터 로드**(처음에는 꺼짐): 작업 인화와 함께 저장한 메타데이터도 되돌립니다.
 
-<!-- panel:edit_history src:57abcbf1 -->
+<!-- panel:edit_history src:59f9ee38 -->
 ## 편집 기록
 
-내가 한 모든 변경을 최신순으로 보여줍니다(최근 100개). **현재**는 지금 상태입니다. 실행 취소 뒤에는 다음 편집 전까지 이후 단계가 **취소됨**으로 표시됩니다. 단계를 클릭하면 그 상태로 돌아갑니다. **⋮** 또는 오른쪽 클릭 → **이 버전 내보내기…**로 지난 상태를 내보냅니다.
+내가 한 모든 변경을 최신순으로 보여줍니다(최근 100개). **현재**는 지금 상태입니다. 실행 취소 뒤에는 다음 편집 전까지 이후 단계가 **취소됨**으로 표시됩니다. 단계를 클릭하면 그 상태로 돌아갑니다. **⋮** 또는 오른쪽 클릭 → **이 버전 내보내기…**로 지난 상태를 내보냅니다. **이 단계와 비교**는 그 단계를 왼쪽에 두고 현재 자르기로 **전/후**를 엽니다. `\`를 누르면 닫힙니다.
 
 <!-- panel:film src:7e289624 -->
 ## 기본 설정

negpy/translations/USER_GUIDE.zh_CN.md

@@ -285,20 +285,20 @@ NegPy 通过虚拟暗房将胶片扫描制作为正像。源图像保持原样
 - **保存…**：选择当前设置中哪些保存为新预设。预设可保存裁切和光学设置及平场配置，但从不保存单帧的裁切、旋转或翻转。
 - **笔**和**垃圾桶**：编辑或删除所选预设。
 
-<!-- panel:work_prints src:e8bf683e -->
+<!-- panel:work_prints src:6d4f4720 -->
 ## 工作样片
 
 **工作样片**是你以名称保留的此帧版本，就像得到最终照片前的试印。
 
 - **保存工作样片…**（`Ctrl+Shift+S`）保留当前编辑。
 - **点击**工作样片即可使用。`Ctrl+Z` 返回。
-- **⋮** 或右键：**导出此版本…**、**重命名…**或**删除…**。
+- **⋮** 或右键：**与此版本对比**、**导出此版本…**、**重命名…**或**删除…**。**与此版本对比**会打开**前后对比**，工作样片在左侧。
 - **加载元数据**（初始关闭）：同时恢复随工作样片保存的元数据。
 
-<!-- panel:edit_history src:57abcbf1 -->
+<!-- panel:edit_history src:59f9ee38 -->
 ## 编辑历史
 
-你做过的每一次更改，最新的在上（保留最近 100 次）。**当前**标出现在的状态；撤销后，之后的步骤会显示为**已撤销**，直到你下一次编辑。点击某一步即可回到那时的状态。**⋮** 或右键 → **导出此版本…**可导出过去的状态。
+你做过的每一次更改，最新的在上（保留最近 100 次）。**当前**标出现在的状态；撤销后，之后的步骤会显示为**已撤销**，直到你下一次编辑。点击某一步即可回到那时的状态。**⋮** 或右键 → **导出此版本…**可导出过去的状态。**与此步骤对比**会以当前裁剪打开**前后对比**，该步骤在左侧。按 `\` 关闭。
 
 <!-- panel:film src:7e289624 -->
 ## 基础设置

negpy/translations/ja.json

@@ -521,6 +521,8 @@
   "Combines the short and long exposure fusion with multi-pass stacking for the most range and least noise, the slowest option.": "短い露出と長い露出の合成をマルチパス スタッキングと組み合わせ、レンジを最大に、ノイズを最小にします。最も遅いオプションです。",
   "Commit the solved print (Enter)": "求めたプリントを確定します (Enter)",
   "Compare": "比較",
+  "Compare With This Step": "このステップと比較",
+  "Compare With This Version": "このバージョンと比較",
   "Composition guide shown in the crop tool": "トリミングツールに表示する構図ガイド",
   "Compression": "圧縮",
   "Compute and Save": "計算して保存する",
@@ -2090,6 +2092,7 @@
   "SELECTED MASK": "選択中のマスク",
   "SIZE": "サイズ",
   "SPLIT TONING": "スプリットトーン",
+  "STEP {number}": "ステップ {number}",
   "Sabattier": "サバティエ",
   "Sabattier Strength": "サバティエの強さ",
   "Sabattier Strength ↑/↓": "サバティエの強さ ↑/↓",