feat(view): DVIEW twists the view about its line of sight

DVIEW (alias DV) offers TWist and Undo. TWist rolls the active view
or viewport camera to the typed angle; Undo steps back through the
twists made in the session. The new alias reaches existing profiles
through the alias migration table.

Refs #638

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

assets/ocad.pgp

@@ -155,6 +155,7 @@ SHA,      *SHADEMODE
 COL,      *COLOR
 DR,       *DRAWORDER
 DS,       *DSETTINGS
+DV,       *DVIEW
 LT,       *LINETYPE
 LTS,      *LTSCALE
 OS,       *OSNAP

locales/ar-SA/opencadstudio.ftl

@@ -4459,6 +4459,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <layer> = تجميد | T <layer> = إلغاء التجميد | Enter = خروج
 
 view =
+    .twist-option = لف
+    .dview-specify-view-twist-angle = DVIEW  حدد زاوية لف العرض <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  أدخل خيارًا [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = تم تعيين نظام الألوان على "النظام" (حاليًا __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = يتطلب عددًا صحيحًا بين __ocs_fmt_0__ و __ocs_fmt_1__.

locales/bg-BG/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <слой> = Замрази  |  T <слой> = Размрази  |  Enter = Изход
 
 view =
+    .twist-option = Завъртане
+    .dview-specify-view-twist-angle = DVIEW  Задайте ъгъл на завъртане на изгледа <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Въведете опция [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Цветовата схема е зададена на „Системна“ (в момента __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Изисква се цяло число между __ocs_fmt_0__ и __ocs_fmt_1__.

locales/cs-CZ/opencadstudio.ftl

@@ -4444,6 +4444,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Zmrazit | T <layer> = Rozmrazit | Enter = Konec
 
 view =
+    .twist-option = Natočení
+    .dview-specify-view-twist-angle = DVIEW  Zadejte úhel natočení pohledu <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Zadejte možnost [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Barevné schéma nastaveno na „Systém“ (aktuálně __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Vyžaduje celé číslo mezi __ocs_fmt_0__ a __ocs_fmt_1__.

locales/de-DE/opencadstudio.ftl

@@ -4445,6 +4445,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <Ebene> = Einfrieren | T <Ebene> = Auftauen | Eingabe = Beenden
 
 view =
+    .twist-option = Verdrehen
+    .dview-specify-view-twist-angle = DVIEW  Ansichtsverdrehwinkel angeben <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Option eingeben [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Farbschema auf „System“ eingestellt (derzeit __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Erfordert eine ganze Zahl zwischen __ocs_fmt_0__ und __ocs_fmt_1__.

locales/el-GR/opencadstudio.ftl

@@ -4447,6 +4447,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <επίπεδο> = Πάγωμα  |  T <επίπεδο> = Ξεπάγωμα  |  Enter = Έξοδος
 
 view =
+    .twist-option = Στρέψη
+    .dview-specify-view-twist-angle = DVIEW  Καθορίστε γωνία στρέψης όψης <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Εισαγάγετε επιλογή [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Ο χρωματικός συνδυασμός ρυθμίστηκε σε „Σύστημα“ (αυτή τη στιγμή __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Απαιτείται ακέραιος αριθμός μεταξύ __ocs_fmt_0__ και __ocs_fmt_1__.

locales/en-US/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <layer> = Freeze  |  T <layer> = Thaw  |  Enter = Exit
 
 view =
+    .twist-option = TWist
+    .dview-specify-view-twist-angle = DVIEW  Specify view twist angle <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Enter option [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Color scheme set to 'System' (currently __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Requires an integer between __ocs_fmt_0__ and __ocs_fmt_1__.

locales/es-ES/opencadstudio.ftl

@@ -4447,6 +4447,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <capa> = Inutilizar | T <capa> = Reutilizar | Intro = Salir
 
 view =
+    .twist-option = Girar
+    .dview-specify-view-twist-angle = DVIEW  Precise el ángulo de giro de la vista <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Indique una opción [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Esquema de color establecido en «Sistema» (actualmente __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Requiere un número entero entre __ocs_fmt_0__ y __ocs_fmt_1__.

locales/fi-FI/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Jäädytys | T <layer> = Sulatus | Enter = Poistu
 
 view =
+    .twist-option = Kierto
+    .dview-specify-view-twist-angle = DVIEW  Määritä näkymän kiertokulma <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Anna valinta [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Väriteema asetettu arvoon "Järjestelmä" (tällä hetkellä __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Vaatii kokonaisluvun väliltä __ocs_fmt_0__–__ocs_fmt_1__.

locales/fr-FR/opencadstudio.ftl

@@ -4448,6 +4448,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Freeze , T <layer> = Thaw , Entrée = Sortie
 
 view =
+    .twist-option = Rotation
+    .dview-specify-view-twist-angle = DVIEW  Spécifiez l’angle de rotation de la vue <__ocs_fmt_0__> :
+    .dview-enter-option-twist-undo = DVIEW  Entrez une option [TWist/Undo] :
     .color-scheme-set-to-system-currently-name = Jeu de couleurs défini sur « Système » (actuellement __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Nécessite un nombre entier compris entre __ocs_fmt_0__ et __ocs_fmt_1__.

locales/hi-IN/opencadstudio.ftl

@@ -4435,6 +4435,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <लेयर> = फ़्रीज़ | T <लेयर> = थॉ | Enter = बाहर निकलें
 
 view =
+    .twist-option = घुमाव
+    .dview-specify-view-twist-angle = DVIEW  दृश्य घुमाव कोण निर्दिष्ट करें <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  विकल्प दर्ज करें [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = रंग योजना 'सिस्टम' पर सेट की गई (वर्तमान में __ocs_fmt_0__)।
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = __ocs_fmt_0__ और __ocs_fmt_1__ के बीच एक पूर्णांक आवश्यक है।

locales/hu-HU/opencadstudio.ftl

@@ -4444,6 +4444,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Fagyasztás | T <layer> = Felengedés | Enter = Kilépés
 
 view =
+    .twist-option = Elforgatás
+    .dview-specify-view-twist-angle = DVIEW  Adja meg a nézet elforgatási szögét <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Adja meg a lehetőséget [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Színséma beállítva: „Rendszer” (jelenleg __ocs_fmt_0__).
     .ss-create-sheet-set = Tervlapkészlet létrehozása
     .ss-requires-integer-between = __ocs_fmt_0__ és __ocs_fmt_1__ közötti egész szám szükséges.

locales/it-IT/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Congela | T <layer> = Scongela | Enter = Esci
 
 view =
+    .twist-option = Rotazione
+    .dview-specify-view-twist-angle = DVIEW  Specificare l'angolo di rotazione della vista <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Immettere un'opzione [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Combinazione colori impostata su "Sistema" (attualmente __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Richiede un numero intero compreso tra __ocs_fmt_0__ e __ocs_fmt_1__.

locales/ja-JP/opencadstudio.ftl

@@ -4435,6 +4435,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <layer> = フリーズ  |  T <layer> = フリーズ解除  |  Enter = 終了
 
 view =
+    .twist-option = ねじれ
+    .dview-specify-view-twist-angle = DVIEW  ビューのねじれ角度を指定 <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  オプションを入力 [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = カラースキームを「システム」に設定しました（現在: __ocs_fmt_0__）。
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = __ocs_fmt_0__ から __ocs_fmt_1__ までの整数が必要です。

locales/ko-KR/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = 동결 | T <layer> = 해동 | Enter = 종료
 
 view =
+    .twist-option = 비틀기
+    .dview-specify-view-twist-angle = DVIEW  뷰 비틀기 각도 지정 <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  옵션 입력 [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = 색 구성표가 '시스템'으로 설정되었습니다(현재 __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = __ocs_fmt_0__에서 __ocs_fmt_1__ 사이의 정수가 필요합니다.

locales/lo-LA/opencadstudio.ftl

@@ -4447,6 +4447,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <ເລເຢີ> = ແຊ່ແຂງ  |  T <ເລເຢີ> = ລະລາຍ  |  Enter = ອອກ
 
 view =
+    .twist-option = ບິດ
+    .dview-specify-view-twist-angle = DVIEW  ກຳນົດມຸມບິດມຸມມອງ <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  ໃສ່ຕົວເລືອກ [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = ຕັ້ງຮູບແບບສີເປັນ 'ລະບົບ' ແລ້ວ (ປັດຈຸບັນ __ocs_fmt_0__).
     .ss-create-sheet-set = ສ້າງຊຸດແຜ່ນງານ
     .ss-requires-integer-between = ຕ້ອງການຈໍານວນຖ້ວນລະຫວ່າງ __ocs_fmt_0__ ຫາ __ocs_fmt_1__.

locales/nl-NL/opencadstudio.ftl

@@ -4445,6 +4445,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <laag> = Bevriezen | T <laag> = Ontdooien | Enter = Afsluiten
 
 view =
+    .twist-option = Draaien
+    .dview-specify-view-twist-angle = DVIEW  Geef weergavedraaihoek op <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Geef optie op [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Kleurenschema ingesteld op 'Systeem' (momenteel __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Vereist een geheel getal tussen __ocs_fmt_0__ en __ocs_fmt_1__.

locales/pl-PL/opencadstudio.ftl

@@ -4446,6 +4446,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <layer> = Zamrożenie | T <layer> = Odwilż | Enter = Wyjście
 
 view =
+    .twist-option = Skręcenie
+    .dview-specify-view-twist-angle = DVIEW  Określ kąt skręcenia widoku <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Podaj opcję [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Schemat kolorów ustawiono na „System” (obecnie __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Wymagana liczba całkowita z zakresu od __ocs_fmt_0__ do __ocs_fmt_1__.

locales/pt-BR/opencadstudio.ftl

@@ -4447,6 +4447,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <camada> = Congelar | T <camada> = Descongelar | Enter = Sair
 
 view =
+    .twist-option = Girar
+    .dview-specify-view-twist-angle = DVIEW  Especifique o ângulo de giro da vista <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Informe uma opção [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Esquema de cores definido como "Sistema" (atualmente __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Requer um número inteiro entre __ocs_fmt_0__ e __ocs_fmt_1__.

locales/ru-RU/opencadstudio.ftl

@@ -4448,6 +4448,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER F <слой> = заморозить | T <слой> = разморозить | Enter = выход
 
 view =
+    .twist-option = Поворот
+    .dview-specify-view-twist-angle = DVIEW  Укажите угол поворота вида <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Задайте параметр [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Цветовая схема установлена на «Системную» (сейчас __ocs_fmt_0__).
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = Требуется целое число от __ocs_fmt_0__ до __ocs_fmt_1__.

locales/tr-TR/opencadstudio.ftl

@@ -4405,6 +4405,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <layer> = Dondur | T <layer> = Çöz | Enter = Çık
 
 view =
+    .twist-option = Döndür
+    .dview-specify-view-twist-angle = DVIEW  Görünüm döndürme açısını belirtin <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  Seçenek girin [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = Renk düzeni 'Sistem' olarak ayarlandı (şu anda __ocs_fmt_0__).
     .ss-create-sheet-set = Sayfa Kümesi Oluştur
     .ss-requires-integer-between = __ocs_fmt_0__ ile __ocs_fmt_1__ arasında bir tam sayı gerekir.

locales/zh-CN/opencadstudio.ftl

@@ -4430,6 +4430,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <图层> = 冻结  |  T <图层> = 解冻  |  Enter = 退出
 
 view =
+    .twist-option = 扭曲
+    .dview-specify-view-twist-angle = DVIEW  指定视图扭曲角度 <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  输入选项 [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = 颜色方案已设为“系统”（当前：__ocs_fmt_0__）。
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = 需要介于 __ocs_fmt_0__ 和 __ocs_fmt_1__ 之间的整数。

locales/zh-TW/opencadstudio.ftl

@@ -4442,6 +4442,9 @@ layout =
     .vplayer-f-layer-freeze-t-layer-thaw-enter-exit = VPLAYER  F <圖層> = 凍結  |  T <圖層> = 解凍  |  Enter = 退出
 
 view =
+    .twist-option = 扭轉
+    .dview-specify-view-twist-angle = DVIEW  指定視圖扭轉角度 <__ocs_fmt_0__>:
+    .dview-enter-option-twist-undo = DVIEW  輸入選項 [TWist/Undo]:
     .color-scheme-set-to-system-currently-name = 配色方案已設為「系統」（目前：__ocs_fmt_0__）。
     .ss-create-sheet-set = Create Sheet Set
     .ss-requires-integer-between = 需要介於 __ocs_fmt_0__ 和 __ocs_fmt_1__ 之間的整數。

src/app/alias.rs

@@ -80,7 +80,7 @@ const WEB_ALIAS_KEY: &str = "opencadstudio.aliases";
 /// migrated forward (see `introduced_at` / `migrate_aliases`). Version 1 shipped
 /// the pre-REDRAW table; version 2 introduced the REDRAW-family aliases; version 3
 /// introduced HB (HATCHTOBACK); version 4 introduced ER (EXTERNALREFERENCES).
-const DEFAULT_ALIASES_VERSION: u32 = 6;
+const DEFAULT_ALIASES_VERSION: u32 = 7;
 
 #[cfg(target_arch = "wasm32")]
 const WEB_ALIAS_VERSION_KEY: &str = "opencadstudio.aliases.version";
@@ -101,6 +101,7 @@ fn introduced_at(version: u32) -> &'static [(&'static str, &'static str)] {
         4 => &[("ER", "EXTERNALREFERENCES")],
         5 => &[("-ATT", "-ATTDEF")],
         6 => &[("VV", "QLAYER")],
+        7 => &[("DV", "DVIEW")],
         _ => &[],
     }
 }

src/app/command_driver/mod.rs

@@ -882,6 +882,9 @@ impl OpenCADStudio {
             CmdResult::ZoomToWindow { p1, p2 } => {
                 self.handle_zoom_to_window(p1, p2);
             }
+            CmdResult::TwistView(twist) => {
+                self.handle_twist_view(twist);
+            }
             CmdResult::Measurement(msg) => {
                 self.handle_measurement(msg);
             }

src/app/command_driver/viewport.rs

@@ -447,6 +447,26 @@ impl OpenCADStudio {
             .push_output(crate::t!("Zoom Window").as_ref());
     }
 
+    /// Turn the active view about its line of sight so the drawing shows
+    /// `twist` radians counter-clockwise from its untwisted orientation.
+    pub(in crate::app) fn handle_twist_view(&mut self, twist: f64) {
+        let i = self.active_tab;
+        self.tabs[i].scene.remember_current_view();
+        let set = |camera: &mut crate::scene::view::camera::Camera| {
+            // The drawing turns one way when the camera rolls the other.
+            camera.roll_by(-twist as f32 - camera.roll());
+        };
+        if self.tabs[i].scene.active_viewport.is_some() {
+            self.tabs[i].scene.mutate_active_viewport_camera(set);
+        } else {
+            set(&mut self.tabs[i].scene.camera.borrow_mut());
+        }
+        self.tabs[i].scene.camera_generation += 1;
+        if let Some(prompt) = self.tabs[i].active_cmd.as_ref().map(|c| c.prompt()) {
+            self.command_line.push_info(&prompt);
+        }
+    }
+
     pub(super) fn handle_set_plot_window(&mut self, p1: glam::DVec3, p2: glam::DVec3) {
         let i = self.active_tab;
         let layout_name = self.tabs[i].scene.current_layout.clone();

src/app/commands/dim.rs

@@ -935,6 +935,21 @@ impl OpenCADStudio {
                 self.tabs[i].active_cmd = Some(Box::new(cmd));
             }
 
+            "DVIEW" => {
+                use crate::modules::view::dview::DviewCommand;
+                let twist = {
+                    let scene = &self.tabs[i].scene;
+                    let roll = match scene.active_viewport {
+                        Some(_) => scene.navigation_camera().roll(),
+                        None => scene.camera.borrow().roll(),
+                    };
+                    -(roll as f64)
+                };
+                let cmd = DviewCommand::new(twist.rem_euclid(std::f64::consts::TAU));
+                self.command_line.push_info(&cmd.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(cmd));
+            }
+
             "ZOOM" | "ZOOM WINDOW" | "ZOOM W" | "ZW" => {
                 use crate::modules::view::zoom_window::ZoomWindowCommand;
                 let new_cmd = ZoomWindowCommand::new();

src/command.rs

@@ -1935,6 +1935,9 @@ pub enum CmdResult {
     PasteClipboard {
         base_pt: DVec3,
     },
+    /// Set the view's twist about its line of sight (radians,
+    /// counter-clockwise); the command stays active.
+    TwistView(f64),
     /// Zoom the model-space camera to fit the given corner points; end command.
     ZoomToWindow {
         p1: DVec3,

src/locale_catalog.rs

@@ -3838,6 +3838,9 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "ZOOM  [Window / Extents / Extents All / All / In / Out / Scale]:" => Some(("view", "zoom-window-extents-extents-all-all-in-out-sca")),
         "ZOOM  scale factor (e.g. 2 or 0.5):" => Some(("annotate", "zoom-scale-factor-e-g-2-or-0-5")),
         "ZOOM WINDOW  Specify first corner:" => Some(("view", "zoom-window-specify-first-corner")),
+        "DVIEW  Enter option [TWist/Undo]:" => Some(("view", "dview-enter-option-twist-undo")),
+        "DVIEW  Specify view twist angle <{current}>:" => Some(("view", "dview-specify-view-twist-angle")),
+        "TWist" => Some(("view", "twist-option")),
         "ZOOM WINDOW  Specify opposite corner:" => Some(("view", "zoom-window-specify-opposite-corner")),
         "Zero" => Some(("properties", "zero")),
         "Zero suppress (DIMALTZ)" => Some(("common", "zero-suppress-dimaltz")),

src/modules/view/dview.rs

@@ -0,0 +1,89 @@
+// DVIEW command — turn the view about its line of sight (TWist).
+
+use crate::t;
+use glam::DVec3;
+
+use crate::command::{CadCommand, CmdOption, CmdResult};
+
+pub struct DviewCommand {
+    /// The view's twist when the command started or last changed, radians.
+    current: f64,
+    /// Earlier twists, for Undo.
+    history: Vec<f64>,
+    twist_prompt: bool,
+}
+
+impl DviewCommand {
+    /// `current` is the view's present twist, counter-clockwise, in radians.
+    pub fn new(current: f64) -> Self {
+        Self {
+            current,
+            history: Vec::new(),
+            twist_prompt: false,
+        }
+    }
+}
+
+impl CadCommand for DviewCommand {
+    fn name(&self) -> &'static str {
+        "DVIEW"
+    }
+
+    fn prompt(&self) -> String {
+        if self.twist_prompt {
+            let current = crate::entities::common::format_angle(self.current);
+            crate::tf!("DVIEW  Specify view twist angle <{current}>:").into_owned()
+        } else {
+            t!("DVIEW  Enter option [TWist/Undo]:").into_owned()
+        }
+    }
+
+    fn options(&self) -> Vec<CmdOption> {
+        if self.twist_prompt {
+            return Vec::new();
+        }
+        vec![CmdOption::new("TWist", "TW"), CmdOption::new("Undo", "U")]
+    }
+
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        let text = text.trim();
+        if self.twist_prompt {
+            let twist = crate::entities::common::parse_angle(&text.replace(',', "."))?;
+            self.twist_prompt = false;
+            self.history.push(self.current);
+            self.current = twist;
+            return Some(CmdResult::TwistView(twist));
+        }
+        match text.trim_start_matches('_').to_ascii_uppercase().as_str() {
+            "TW" | "TWIST" => {
+                self.twist_prompt = true;
+                Some(CmdResult::NeedPoint)
+            }
+            "U" | "UNDO" => {
+                let previous = self.history.pop()?;
+                self.current = previous;
+                Some(CmdResult::TwistView(previous))
+            }
+            _ => None,
+        }
+    }
+
+    fn on_point(&mut self, _pt: DVec3) -> CmdResult {
+        CmdResult::NeedPoint
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        if self.twist_prompt {
+            // Enter keeps the current twist and returns to the options.
+            self.twist_prompt = false;
+            return CmdResult::NeedPoint;
+        }
+        CmdResult::Cancel
+    }
+}
+
+inventory::submit!(crate::command::CommandRegistration { names: &["DVIEW"] });

src/modules/view/mod.rs

@@ -5,6 +5,7 @@ mod count_palette;
 mod file_tabs;
 mod graphic_attributes_palette;
 mod layout_tabs;
+pub mod dview;
 pub mod limits;
 mod orbit;
 mod ortho;