Merge branch 'latch' into 'master'

Latch views

See merge request Librem5/squeekboard!416

data/keyboards/pl.yaml

@@ -52,6 +52,8 @@ buttons:
             locking:
                 lock_view: "upper_accents"
                 unlock_view: "accents"
+                looks_locked_from:
+                    - "upper"
         outline: "altline"
         icon: "key-shift"
     BackSpace:
@@ -94,6 +96,8 @@ buttons:
             locking:
                 lock_view: "upper_accents"
                 unlock_view: "upper"
+                looks_locked_from:
+                    - "accents"
         outline: "altline"
         label: "ĄĘ"
     period:

data/style-Adwaita:dark.css

@@ -31,11 +31,16 @@ sq_button.wide {
     border-color: #3e3a44;
 }
 
-sq_button.locked {
+sq_button.latched {
     background: #ffffff;
     color: #2b292f;
 }
 
+sq_button.locked {
+    background: #ffffff;
+    color: #1c71d8;
+}
+
 sq_button.action {
     font-size: 0.75em;
 }

data/style.css

@@ -34,11 +34,16 @@ sq_button.wide {
     border-color: @borders; /* #3e3a44; */
 }
 
-sq_button.locked {
+sq_button.latched {
     background: @theme_fg_color; /*#ffffff;*/
     color: @theme_bg_color; /*#2b292f;*/
 }
 
+sq_button.locked {
+    background: @theme_fg_color; /*#ffffff;*/
+    color: mix(@theme_selected_bg_color, @theme_bg_color, 0.4); /*#2b292f;*/
+}
+
 sq_button.action {
     font-size: 0.75em;
 }

eek/eek-renderer.c

@@ -18,8 +18,6 @@
  * 02110-1301 USA
  */
 
-#include "config.h"
-
 #include <math.h>
 #include <string.h>
 #include <gdk-pixbuf/gdk-pixbuf.h>
@@ -33,10 +31,6 @@
 static void render_button_label (cairo_t *cr, GtkStyleContext *ctx,
                                                 const gchar *label, EekBounds bounds);
 
-void eek_render_button                         (EekRenderer *self,
-                                                cairo_t     *cr, const struct squeek_button *button,
-                                                gboolean     pressed, gboolean locked);
-
 static void
 render_outline (cairo_t     *cr,
                 GtkStyleContext *ctx,
@@ -60,21 +54,21 @@ render_outline (cairo_t     *cr,
         position.x, position.y, position.width, position.height);
 }
 
-static void render_button_in_context(gint scale_factor,
+/// Rust interface
+void eek_render_button_in_context(uint32_t scale_factor,
                                      cairo_t     *cr,
                                      GtkStyleContext *ctx,
-                                     const struct squeek_button *button) {
+                                     EekBounds bounds,
+                                     const char *icon_name,
+                                     const gchar *label) {
     /* blank background */
     cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.0);
     cairo_paint (cr);
 
-    EekBounds bounds = squeek_button_get_bounds(button);
     render_outline (cr, ctx, bounds);
     cairo_paint (cr);
 
     /* render icon (if any) */
-    const char *icon_name = squeek_button_get_icon_name(button);
-
     if (icon_name) {
         cairo_surface_t *icon_surface =
             eek_renderer_get_icon_surface (icon_name, 16, scale_factor);
@@ -104,25 +98,27 @@ static void render_button_in_context(gint scale_factor,
         }
     }
 
-    const gchar *label = squeek_button_get_label(button);
     if (label) {
-        render_button_label (cr, ctx, label, squeek_button_get_bounds(button));
+        render_button_label (cr, ctx, label, bounds);
     }
 }
 
-void
+/// Prepare context for drawing the button.
-eek_render_button (EekRenderer *self,
+/// The context MUST be released using the corresponing "put" procedure
-            cairo_t     *cr,
+/// before drawing the next button.
-            const struct squeek_button *button,
+/// Interface for Rust.
-               gboolean     pressed,
+GtkStyleContext *
-               gboolean     locked)
+eek_get_style_context_for_button (EekRenderer *self,
+                                  const char *name,
+                                  const char *outline_name,
+                                  const char *locked_class,
+               uint64_t     pressed)
 {
     GtkStyleContext *ctx = self->button_context;
     /* Set the name of the button on the widget path, using the name obtained
        from the button's symbol. */
     g_autoptr (GtkWidgetPath) path = NULL;
     path = gtk_widget_path_copy (gtk_style_context_get_path (ctx));
-    const char *name = squeek_button_get_name(button);
     gtk_widget_path_iter_set_name (path, -1, name);
 
     /* Update the style context with the updated widget path. */
@@ -131,19 +127,22 @@ eek_render_button (EekRenderer *self,
        (pressed) or normal. */
     gtk_style_context_set_state(ctx,
         pressed ? GTK_STATE_FLAG_ACTIVE : GTK_STATE_FLAG_NORMAL);
-    const char *outline_name = squeek_button_get_outline_name(button);
+    if (locked_class) {
-    if (locked) {
+        gtk_style_context_add_class(ctx, locked_class);
-        gtk_style_context_add_class(ctx, "locked");
     }
     gtk_style_context_add_class(ctx, outline_name);
+    return ctx;
+}
 
-    render_button_in_context(self->scale_factor, cr, ctx, button);
+/// Interface for Rust.
-
+void eek_put_style_context_for_button(GtkStyleContext *ctx,
+                                      const char *outline_name,
+                                      const char *locked_class) {
     // Save and restore functions don't work if gtk_render_* was used in between
     gtk_style_context_set_state(ctx, GTK_STATE_FLAG_NORMAL);
     gtk_style_context_remove_class(ctx, outline_name);
-    if (locked) {
+    if (locked_class) {
-        gtk_style_context_remove_class(ctx, "locked");
+        gtk_style_context_remove_class(ctx, locked_class);
     }
 }
 
@@ -328,6 +327,11 @@ eek_renderer_set_scale_factor (EekRenderer *renderer, gint scale)
     renderer->scale_factor = scale;
 }
 
+/// Rust interface.
+uint32_t eek_renderer_get_scale_factor(EekRenderer *renderer) {
+    return renderer->scale_factor;
+}
+
 cairo_surface_t *
 eek_renderer_get_icon_surface (const gchar *icon_name,
                                gint size,

eek/eek-types.h

@@ -90,13 +90,5 @@ struct transformation {
     gdouble scale;
 };
 
-struct squeek_button;
-struct squeek_row;
-
-/// Represents the path to the button within a view
-struct button_place {
-    const struct squeek_row *row;
-    const struct squeek_button *button;
-};
 G_END_DECLS
 #endif  /* EEK_TYPES_H */

src/action.rs

@@ -10,7 +10,7 @@ pub struct KeySym(pub String);
 type View = String;
 
 /// Use to send modified keypresses
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Modifier {
     /// Control and Alt are the only modifiers
     /// which doesn't interfere with levels,
@@ -30,6 +30,11 @@ pub enum Action {
         lock: View,
         /// When unlocked by pressing it or emitting a key
         unlock: View,
+        /// Whether key has a latched state
+        /// that pops when another key is pressed.
+        latches: bool,
+        /// Should take on *locked* appearance whenever latch comes back to those views.
+        looks_locked_from: Vec<View>,
     },
     /// Hold this modifier for as long as the button is pressed
     ApplyModifier(Modifier),
@@ -49,14 +54,24 @@ pub enum Action {
 impl Action {
     pub fn is_locked(&self, view_name: &str) -> bool {
         match self {
-            Action::LockView { lock, unlock: _ } => lock == view_name,
+            Action::LockView { lock, unlock: _, latches: _, looks_locked_from: _ } => lock == view_name,
+            _ => false,
+        }
+    }
+    pub fn has_locked_appearance_from(&self, locked_view_name: &str) -> bool {
+        match self {
+            Action::LockView { lock: _, unlock: _, latches: _, looks_locked_from } => {
+                looks_locked_from.iter()
+                    .find(|view| locked_view_name == view.as_str())
+                    .is_some()
+            },
             _ => false,
         }
     }
     pub fn is_active(&self, view_name: &str) -> bool {
         match self {
             Action::SetView(view) => view == view_name,
-            Action::LockView { lock, unlock: _ } => lock == view_name,
+            Action::LockView { lock, unlock: _, latches: _, looks_locked_from: _ } => lock == view_name,
             _ => false,
         }
     }

src/data.rs

@@ -289,7 +289,13 @@ struct ButtonMeta {
 #[serde(deny_unknown_fields)]
 enum Action {
     #[serde(rename="locking")]
-    Locking { lock_view: String, unlock_view: String },
+    Locking {
+        lock_view: String,
+        unlock_view: String,
+        pops: Option<bool>,
+        #[serde(default)]
+        looks_locked_from: Vec<String>,
+    },
     #[serde(rename="set_view")]
     SetView(String),
     #[serde(rename="show_prefs")]
@@ -600,7 +606,9 @@ fn create_action<H: logging::Handler>(
             )
         ),
         SubmitData::Action(Action::Locking {
-            lock_view, unlock_view
+            lock_view, unlock_view,
+            pops,
+            looks_locked_from,
         }) => ::action::Action::LockView {
             lock: filter_view_name(
                 name,
@@ -614,6 +622,8 @@ fn create_action<H: logging::Handler>(
                 &view_names,
                 warning_handler,
             ),
+            latches: pops.unwrap_or(true),
+            looks_locked_from,
         },
         SubmitData::Action(
             Action::ShowPrefs

src/drawing.rs

@@ -3,20 +3,24 @@
 use cairo;
 use std::cell::RefCell;
 
-use ::action::Action;
+use ::action::{ Action, Modifier };
 use ::keyboard;
-use ::layout::{ Button, Layout };
+use ::layout::{ Button, Label, LatchedState, Layout };
-use ::layout::c::{ EekGtkKeyboard, Point };
+use ::layout::c::{ Bounds, EekGtkKeyboard, Point };
 use ::submission::Submission;
 
 use glib::translate::FromGlibPtrNone;
 use gtk::WidgetExt;
 
+use std::collections::HashSet;
+use std::ffi::CStr;
+use std::ptr;
+
 mod c {
     use super::*;
 
     use cairo_sys;
-    use std::os::raw::c_void;
+    use std::os::raw::{ c_char, c_void };
     
     // This is constructed only in C, no need for warnings
     #[allow(dead_code)]
@@ -24,17 +28,44 @@ mod c {
     #[derive(Clone, Copy)]
     pub struct EekRenderer(*const c_void);
 
+    // This is constructed only in C, no need for warnings
+    /// Just don't clone this for no reason.
+    #[allow(dead_code)]
+    #[repr(transparent)]
+    #[derive(Clone, Copy)]
+    pub struct GtkStyleContext(*const c_void);
+
+
     extern "C" {
-        // Button and View inside CButtonPlace are safe to pass to C
-        // as long as they don't outlive the call
-        // and nothing dereferences them
         #[allow(improper_ctypes)]
-        pub fn eek_render_button(
+        pub fn eek_renderer_get_scale_factor(
             renderer: EekRenderer,
+        ) -> u32;
+
+        #[allow(improper_ctypes)]
+        pub fn eek_render_button_in_context(
+            scale_factor: u32,
             cr: *mut cairo_sys::cairo_t,
-            button: *const Button,
+            ctx: GtkStyleContext,
+            bounds: Bounds,
+            icon_name: *const c_char,
+            label: *const c_char,
+        );
+
+        #[allow(improper_ctypes)]
+        pub fn eek_get_style_context_for_button(
+            renderer: EekRenderer,
+            name: *const c_char,
+            outline_name: *const c_char,
+            locked_class: *const c_char,
             pressed: u64,
-            locked: u64,
+        ) -> GtkStyleContext;
+
+        #[allow(improper_ctypes)]
+        pub fn eek_put_style_context_for_button(
+            ctx: GtkStyleContext,
+            outline_name: *const c_char,
+            locked_class: *const c_char,
         );
     }
 
@@ -54,13 +85,16 @@ mod c {
 
         layout.foreach_visible_button(|offset, button| {
             let state = RefCell::borrow(&button.state).clone();
-            let active_mod = match &state.action {
+
-                Action::ApplyModifier(m) => active_modifiers.contains(m),
+            let locked = LockedStyle::from_action(
-                _ => false,
+                &state.action,
-            };
+                &active_modifiers,
-            let locked = state.action.is_active(&layout.current_view)
+                layout.get_view_latched(),
-                | active_mod;
+                &layout.current_view,
-            if state.pressed == keyboard::PressType::Pressed || locked {
+            );
+            if state.pressed == keyboard::PressType::Pressed
+                || locked != LockedStyle::Free
+            {
                 render_button_at_position(
                     renderer, &cr,
                     offset,
@@ -86,20 +120,55 @@ mod c {
                 renderer, &cr,
                 offset,
                 button.as_ref(),
-                keyboard::PressType::Released, false,
+                keyboard::PressType::Released,
+                LockedStyle::Free,
             );
         })
     }
 }
 
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum LockedStyle {
+    Free,
+    Latched,
+    Locked,
+}
+
+impl LockedStyle {
+    fn from_action(
+        action: &Action,
+        mods: &HashSet<Modifier>,
+        latched_view: &LatchedState,
+        current_view: &str,
+    ) -> LockedStyle {
+        let active_mod = match action {
+            Action::ApplyModifier(m) => mods.contains(m),
+            _ => false,
+        };
+        
+        let active_view = action.is_active(current_view);
+        let latched_button = match latched_view {
+            LatchedState::Not => false,
+            LatchedState::FromView(view) => !action.has_locked_appearance_from(view),
+        };
+        match (active_mod, active_view, latched_button) {
+            // Modifiers don't latch.
+            (true, _, _) => LockedStyle::Locked,
+            (false, true, false) => LockedStyle::Locked,
+            (false, true, true) => LockedStyle::Latched,
+            _ => LockedStyle::Free,
+        }
+    }
+}
+
 /// Renders a button at a position (button's own bounds ignored)
-pub fn render_button_at_position(
+fn render_button_at_position(
     renderer: c::EekRenderer,
     cr: &cairo::Context,
     position: Point,
     button: &Button,
     pressed: keyboard::PressType,
-    locked: bool,
+    locked: LockedStyle,
 ) {
     cr.save();
     cr.translate(position.x, position.y);
@@ -108,19 +177,110 @@ pub fn render_button_at_position(
         button.size.width, button.size.height
     );
     cr.clip();
-    unsafe {
+
-        c::eek_render_button(
+    let scale_factor = unsafe {
+        c::eek_renderer_get_scale_factor(renderer)
+    };
+    let bounds = button.get_bounds();
+    let (label_c, icon_name_c) = match &button.label {
+        Label::Text(text) => (text.as_ptr(), ptr::null()),
+        Label::IconName(name) => {
+            let l = unsafe {
+                // CStr doesn't allocate anything, so it only points to
+                // the 'static str, avoiding a memory leak
+                CStr::from_bytes_with_nul_unchecked(b"icon\0")
+            };
+            (l.as_ptr(), name.as_ptr())
+        },
+    };
+
+    with_button_context(
+        renderer,
+        button,
+        pressed,
+        locked,
+        |ctx| unsafe {
+            // TODO: split into separate procedures:
+            // draw outline, draw label, draw icon.
+            c::eek_render_button_in_context(
+                scale_factor,
+                cairo::Context::to_raw_none(&cr),
+                *ctx,
+                bounds,
+                icon_name_c,
+                label_c,
+            )
+        }
+    );
+
+    cr.restore();
+}
+
+fn with_button_context<R, F: FnOnce(&c::GtkStyleContext) -> R>(
+    renderer: c::EekRenderer,
+    button: &Button,
+    pressed: keyboard::PressType,
+    locked: LockedStyle,
+    operation: F,
+) -> R {
+    let outline_name_c = button.outline_name.as_ptr();
+    let locked_class_c = match locked {
+        LockedStyle::Free => ptr::null(),
+        LockedStyle::Locked => unsafe {
+            CStr::from_bytes_with_nul_unchecked(b"locked\0").as_ptr()
+        },
+        LockedStyle::Latched => unsafe {
+            CStr::from_bytes_with_nul_unchecked(b"latched\0").as_ptr()
+        },
+    };
+    
+    let ctx = unsafe {
+        c::eek_get_style_context_for_button(
             renderer,
-            cairo::Context::to_raw_none(&cr),
+            button.name.as_ptr(),
-            button as *const Button,
+            outline_name_c,
+            locked_class_c,
             pressed as u64,
-            locked as u64,
         )
     };
-    cr.restore();
+    
+    let r = operation(&ctx);
+
+    unsafe {
+        c::eek_put_style_context_for_button(
+            ctx,
+            outline_name_c,
+            locked_class_c,
+        )
+    };
+
+    r
 }
 
 pub fn queue_redraw(keyboard: EekGtkKeyboard) {
     let widget = unsafe { gtk::Widget::from_glib_none(keyboard.0) };
     widget.queue_draw();
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_exit_only() {
+        assert_eq!(
+            LockedStyle::from_action(
+                &Action::LockView {
+                    lock: "ab".into(), 
+                    unlock: "a".into(),
+                    latches: true,
+                    looks_locked_from: vec!["b".into()],
+                },
+                &HashSet::new(),
+                &LatchedState::FromView("b".into()),
+                "ab",
+            ),
+            LockedStyle::Locked,
+        );
+    }
+}

src/layout.h

@@ -26,13 +26,6 @@ struct squeek_layout_state {
 
 struct squeek_layout;
 
-EekBounds squeek_button_get_bounds(const struct squeek_button*);
-const char *squeek_button_get_label(const struct squeek_button*);
-const char *squeek_button_get_icon_name(const struct squeek_button*);
-const char *squeek_button_get_name(const struct squeek_button*);
-const char *squeek_button_get_outline_name(const struct squeek_button*);
-
-void squeek_button_print(const struct squeek_button* button);
 
 struct transformation squeek_layout_calculate_transformation(
         const struct squeek_layout *layout,

src/layout.rs

@@ -41,9 +41,7 @@ pub mod c {
     use super::*;
 
     use gtk_sys;
-    use std::ffi::CStr;
+    use std::os::raw::c_void;
-    use std::os::raw::{ c_char, c_void };
-    use std::ptr;
 
     use std::ops::{ Add, Sub };
 
@@ -161,64 +159,6 @@ pub mod c {
     pub struct LevelKeyboard(*const c_void);
 
     // The following defined in Rust. TODO: wrap naked pointers to Rust data inside RefCells to prevent multiple writers
-
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_get_bounds(button: *const ::layout::Button) -> Bounds {
-        let button = unsafe { &*button };
-        Bounds {
-            x: 0.0, y: 0.0,
-            width: button.size.width, height: button.size.height
-        }
-    }
-
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_get_label(
-        button: *const ::layout::Button
-    ) -> *const c_char {
-        let button = unsafe { &*button };
-        match &button.label {
-            Label::Text(text) => text.as_ptr(),
-            // returning static strings to C is a bit cumbersome
-            Label::IconName(_) => unsafe {
-                // CStr doesn't allocate anything, so it only points to
-                // the 'static str, avoiding a memory leak
-                CStr::from_bytes_with_nul_unchecked(b"icon\0")
-            }.as_ptr(),
-        }
-    }
-    
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_get_icon_name(button: *const Button) -> *const c_char {
-        let button = unsafe { &*button };
-        match &button.label {
-            Label::Text(_) => ptr::null(),
-            Label::IconName(name) => name.as_ptr(),
-        }
-    }
-    
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_get_name(button: *const Button) -> *const c_char {
-        let button = unsafe { &*button };
-        button.name.as_ptr()
-    }
-    
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_get_outline_name(button: *const Button) -> *const c_char {
-        let button = unsafe { &*button };
-        button.outline_name.as_ptr()
-    }
-    
-    #[no_mangle]
-    pub extern "C"
-    fn squeek_button_print(button: *const ::layout::Button) {
-        let button = unsafe { &*button };
-        println!("{:?}", button);
-    }
     
     /// Positions the layout contents within the available space.
     /// The origin of the transformation is the point inside the margins.
@@ -484,6 +424,15 @@ pub struct Button {
     pub state: Rc<RefCell<KeyState>>,
 }
 
+impl Button {
+    pub fn get_bounds(&self) -> c::Bounds {
+        c::Bounds {
+            x: 0.0, y: 0.0,
+            width: self.size.width, height: self.size.height,
+        }
+    }
+}
+
 /// The graphical representation of a row of buttons
 #[derive(Clone, Debug)]
 pub struct Row {
@@ -551,6 +500,7 @@ pub struct Spacing {
     pub button: f64,
 }
 
+#[derive(Clone)]
 pub struct View {
     /// Rows together with their offsets from the top left
     rows: Vec<(c::Point, Row)>,
@@ -664,6 +614,19 @@ pub struct Margins {
     pub right: f64,
 }
 
+#[derive(Clone, Debug, PartialEq)]
+pub enum LatchedState {
+    /// Holds view to return to.
+    FromView(String),
+    Not,
+}
+
+impl LatchedState {
+    pub fn is_latched(&self) -> bool {
+        self != &LatchedState::Not
+    }
+}
+
 // TODO: split into sth like
 // Arrangement (views) + details (keymap) + State (keys)
 /// State of the UI, contains the backend as well
@@ -671,6 +634,12 @@ pub struct Layout {
     pub margins: Margins,
     pub kind: ArrangementKind,
     pub current_view: String,
+
+    // If current view is latched,
+    // clicking any button that emits an action (erase, submit, set modifier)
+    // will cause lock buttons to unlatch.
+    view_latched: LatchedState,
+
     // Views own the actual buttons which have state
     // Maybe they should own UI only,
     // and keys should be owned by a dedicated non-UI-State?
@@ -717,6 +686,7 @@ impl Layout {
         Layout {
             kind,
             current_view: "base".to_owned(),
+            view_latched: LatchedState::Not,
             views: data.views,
             keymaps: data.keymaps,
             pressed_keys: HashSet::new(),
@@ -742,6 +712,12 @@ impl Layout {
         }
     }
 
+    // Layout is passed around mutably,
+    // so better keep the field away from direct access.
+    pub fn get_view_latched(&self) -> &LatchedState {
+        &self.view_latched
+    }
+
     /// Calculates size without margins
     fn calculate_inner_size(&self) -> Size {
         View::calculate_super_size(
@@ -817,8 +793,117 @@ impl Layout {
         }
         out
     }
+    
+    fn apply_view_transition(
+        &mut self,
+        action: &Action,
+    ) {
+        let (transition, new_latched) = Layout::process_action_for_view(
+            action,
+            &self.current_view,
+            &self.view_latched,
+        );
+
+        match transition {
+            ViewTransition::UnlatchAll => self.unstick_locks(),
+            ViewTransition::ChangeTo(view) => try_set_view(self, view.into()),
+            ViewTransition::NoChange => {},
+        };
+
+        self.view_latched = new_latched;
+    }
+
+    /// Unlatch all latched keys,
+    /// so that the new view is the one before first press.
+    fn unstick_locks(&mut self) {
+        if let LatchedState::FromView(name) = self.view_latched.clone() {
+            match self.set_view(name.clone()) {
+                Ok(_) => { self.view_latched = LatchedState::Not; }
+                Err(e) => log_print!(
+                    logging::Level::Bug,
+                    "Bad view {}, can't unlatch ({:?})",
+                    name,
+                    e,
+                ),
+            }
+        }
+    }
+
+    /// Last bool is new latch state.
+    /// It doesn't make sense when the result carries UnlatchAll,
+    /// but let's not be picky.
+    ///
+    /// Although the state is not defined at the keys
+    /// (it's in the relationship between view and action),
+    /// keys go through the following stages when clicked repeatedly: 
+    /// unlocked+unlatched -> locked+latched -> locked+unlatched
+    /// -> unlocked+unlatched
+    fn process_action_for_view<'a>(
+        action: &'a Action,
+        current_view: &str,
+        latched: &LatchedState,
+    ) -> (ViewTransition<'a>, LatchedState) {
+        match action {
+            Action::Submit { text: _, keys: _ }
+                | Action::Erase
+                | Action::ApplyModifier(_)
+            => {
+                let t = match latched {
+                    LatchedState::FromView(_) => ViewTransition::UnlatchAll,
+                    LatchedState::Not => ViewTransition::NoChange,
+                };
+                (t, LatchedState::Not)
+            },
+            Action::SetView(view) => (
+                ViewTransition::ChangeTo(view),
+                LatchedState::Not,
+            ),
+            Action::LockView { lock, unlock, latches, looks_locked_from: _ } => {
+                use self::ViewTransition as VT;
+                let locked = action.is_locked(current_view);
+                match (locked, latched, latches) {
+                    // Was unlocked, now make locked but latched.
+                    (false, LatchedState::Not, true) => (
+                        VT::ChangeTo(lock),
+                        LatchedState::FromView(current_view.into()),
+                    ),
+                    // Layout is latched for reason other than this button.
+                    (false, LatchedState::FromView(view), true) => (
+                        VT::ChangeTo(lock),
+                        LatchedState::FromView(view.clone()),
+                    ),
+                    // Was latched, now only locked.
+                    (true, LatchedState::FromView(_), true)
+                        => (VT::NoChange, LatchedState::Not),
+                    // Was unlocked, can't latch so now make fully locked.
+                    (false, _, false)
+                        => (VT::ChangeTo(lock), LatchedState::Not),
+                    // Was locked, now make unlocked.
+                    (true, _, _)
+                        => (VT::ChangeTo(unlock), LatchedState::Not),
+                }
+            },
+            _ => (ViewTransition::NoChange, latched.clone()),
+        }
+    }
 }
 
+#[derive(Debug, PartialEq)]
+enum ViewTransition<'a> {
+    ChangeTo(&'a str),
+    UnlatchAll,
+    NoChange,
+}
+
+fn try_set_view(layout: &mut Layout, view_name: &str) {
+    layout.set_view(view_name.into())
+        .or_print(
+            logging::Problem::Bug,
+            &format!("Bad view {}, ignoring", view_name),
+        );
+}
+
+
 mod procedures {
     use super::*;
 
@@ -897,67 +982,6 @@ pub struct UIBackend {
 mod seat {
     use super::*;
 
-    fn try_set_view(layout: &mut Layout, view_name: String) {
-        layout.set_view(view_name.clone())
-            .or_print(
-                logging::Problem::Bug,
-                &format!("Bad view {}, ignoring", view_name),
-            );
-    }
-
-    /// A vessel holding an obligation to switch view.
-    /// Use with #[must_use]
-    struct ViewChange<'a> {
-        layout: &'a mut Layout,
-        view_name: Option<String>,
-    }
-    
-    impl<'a> ViewChange<'a> {
-        fn choose_view(self, view_name: String) -> ViewChange<'a> {
-            ViewChange {
-                view_name: Some(view_name),
-                ..self
-            }
-        }
-        fn apply(self) {
-            if let Some(name) = self.view_name {
-                try_set_view(self.layout, name);
-            }
-        }
-    }
-
-    /// Find all impermanent view changes and undo them in an arbitrary order.
-    /// Return an obligation to actually switch the view.
-    /// The final view is the "unlock" view
-    /// from one of the currently stuck keys.
-    // As long as only one stuck button is used, this should be fine.
-    // This is guaranteed because pressing a lock button unlocks all others.
-    // TODO: Make some broader guarantee about the resulting view,
-    // e.g. by maintaining a stack of stuck keys.
-    #[must_use]
-    fn unstick_locks(layout: &mut Layout) -> ViewChange {
-        let mut new_view = None;
-        for key in layout.get_locked_keys().clone() {
-            let key: &Rc<RefCell<KeyState>> = key.borrow();
-            let key = RefCell::borrow(key);
-            match &key.action {
-                Action::LockView { lock: _, unlock: view } => {
-                    new_view = Some(view.clone());
-                },
-                a => log_print!(
-                    logging::Level::Bug,
-                    "Non-locking action {:?} was found inside locked keys",
-                    a,
-                ),
-            };
-        }
-        
-        ViewChange {
-            layout,
-            view_name: new_view,
-        }
-    }
-
     pub fn handle_press_key(
         layout: &mut Layout,
         submission: &mut Submission,
@@ -1017,37 +1041,22 @@ mod seat {
         };
         let action = key.action.clone();
 
+        layout.apply_view_transition(&action);
+
         // update
         let key = key.into_released();
 
-        // process changes
+        // process non-view switching
         match action {
             Action::Submit { text: _, keys: _ }
                 | Action::Erase
             => {
-                unstick_locks(layout).apply();
                 submission.handle_release(KeyState::get_id(rckey), time);
             },
-            Action::SetView(view) => {
-                try_set_view(layout, view)
-            },
-            Action::LockView { lock, unlock } => {
-                let gets_locked = !key.action.is_locked(&layout.current_view);
-                unstick_locks(layout)
-                    // It doesn't matter what the resulting view should be,
-                    // it's getting changed anyway.
-                    .choose_view(
-                        match gets_locked {
-                            true => lock.clone(),
-                            false => unlock.clone(),
-                        }
-                    )
-                    .apply()
-            },
             Action::ApplyModifier(modifier) => {
                 // FIXME: key id is unneeded with stateless locks
                 let key_id = KeyState::get_id(rckey);
-                let gets_locked = !submission.is_modifier_active(modifier.clone());
+                let gets_locked = !submission.is_modifier_active(modifier);
                 match gets_locked {
                     true => submission.handle_add_modifier(
                         key_id,
@@ -1082,6 +1091,8 @@ mod seat {
                     }
                 }
             },
+            // Other keys are handled in view switcher before.
+            _ => {}
         };
 
         let pointer = ::util::Pointer(rckey.clone());
@@ -1099,14 +1110,20 @@ mod test {
     use std::ffi::CString;
     use ::keyboard::PressType;
 
-    pub fn make_state() -> Rc<RefCell<::keyboard::KeyState>> {
+    pub fn make_state_with_action(action: Action)
+        -> Rc<RefCell<::keyboard::KeyState>>
+    {
         Rc::new(RefCell::new(::keyboard::KeyState {
             pressed: PressType::Released,
             keycodes: Vec::new(),
-            action: Action::SetView("default".into()),
+            action,
         }))
     }
 
+    pub fn make_state() -> Rc<RefCell<::keyboard::KeyState>> {
+        make_state_with_action(Action::SetView("default".into()))
+    }
+
     pub fn make_button_with_state(
         name: String,
         state: Rc<RefCell<::keyboard::KeyState>>,
@@ -1120,6 +1137,242 @@ mod test {
         })
     }
     
+    #[test]
+    fn latch_lock_unlock() {
+        let action = Action::LockView {
+            lock: "lock".into(),
+            unlock: "unlock".into(),
+            latches: true,
+            looks_locked_from: vec![],
+        };
+
+        assert_eq!(
+            Layout::process_action_for_view(&action, "unlock", &LatchedState::Not),
+            (ViewTransition::ChangeTo("lock"), LatchedState::FromView("unlock".into())),
+        );
+
+        assert_eq!(
+            Layout::process_action_for_view(&action, "lock", &LatchedState::FromView("unlock".into())),
+            (ViewTransition::NoChange, LatchedState::Not),
+        );
+
+        assert_eq!(
+            Layout::process_action_for_view(&action, "lock", &LatchedState::Not),
+            (ViewTransition::ChangeTo("unlock"), LatchedState::Not),
+        );
+
+        assert_eq!(
+            Layout::process_action_for_view(&Action::Erase, "lock", &LatchedState::FromView("base".into())),
+            (ViewTransition::UnlatchAll, LatchedState::Not),
+        );
+    }
+
+    #[test]
+    fn latch_pop_layout() {
+        let switch = Action::LockView {
+            lock: "locked".into(),
+            unlock: "base".into(),
+            latches: true,
+            looks_locked_from: vec![],
+        };
+        
+        let submit = Action::Erase;
+
+        let view = View::new(vec![(
+            0.0,
+            Row::new(vec![
+                (
+                    0.0,
+                    make_button_with_state(
+                        "switch".into(),
+                        make_state_with_action(switch.clone())
+                    ),
+                ),
+                (
+                    1.0,
+                    make_button_with_state(
+                        "submit".into(),
+                        make_state_with_action(submit.clone())
+                    ),
+                ),
+            ]),
+        )]);
+
+        let mut layout = Layout {
+            current_view: "base".into(),
+            view_latched: LatchedState::Not,
+            keymaps: Vec::new(),
+            kind: ArrangementKind::Base,
+            pressed_keys: HashSet::new(),
+            margins: Margins {
+                top: 0.0,
+                left: 0.0,
+                right: 0.0,
+                bottom: 0.0,
+            },
+            views: hashmap! {
+                // Both can use the same structure.
+                // Switching doesn't depend on the view shape
+                // as long as the switching button is present.
+                "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
+                "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view),
+            },
+        };        
+
+        // Basic cycle
+        layout.apply_view_transition(&switch);
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&switch);
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&submit);
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&switch);
+        assert_eq!(&layout.current_view, "base");
+        layout.apply_view_transition(&switch);
+        // Unlatch
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&submit);
+        assert_eq!(&layout.current_view, "base");
+    }
+
+    #[test]
+    fn reverse_unlatch_layout() {
+        let switch = Action::LockView {
+            lock: "locked".into(),
+            unlock: "base".into(),
+            latches: true,
+            looks_locked_from: vec![],
+        };
+        
+        let unswitch = Action::LockView {
+            lock: "locked".into(),
+            unlock: "unlocked".into(),
+            latches: false,
+            looks_locked_from: vec![],
+        };
+        
+        let submit = Action::Erase;
+
+        let view = View::new(vec![(
+            0.0,
+            Row::new(vec![
+                (
+                    0.0,
+                    make_button_with_state(
+                        "switch".into(),
+                        make_state_with_action(switch.clone())
+                    ),
+                ),
+                (
+                    1.0,
+                    make_button_with_state(
+                        "submit".into(),
+                        make_state_with_action(submit.clone())
+                    ),
+                ),
+            ]),
+        )]);
+
+        let mut layout = Layout {
+            current_view: "base".into(),
+            view_latched: LatchedState::Not,
+            keymaps: Vec::new(),
+            kind: ArrangementKind::Base,
+            pressed_keys: HashSet::new(),
+            margins: Margins {
+                top: 0.0,
+                left: 0.0,
+                right: 0.0,
+                bottom: 0.0,
+            },
+            views: hashmap! {
+                // Both can use the same structure.
+                // Switching doesn't depend on the view shape
+                // as long as the switching button is present.
+                "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
+                "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
+                "unlocked".into() => (c::Point { x: 0.0, y: 0.0 }, view),
+            },
+        };        
+
+        layout.apply_view_transition(&switch);
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&unswitch);
+        assert_eq!(&layout.current_view, "unlocked");
+    }
+
+    #[test]
+    fn latch_twopop_layout() {
+        let switch = Action::LockView {
+            lock: "locked".into(),
+            unlock: "base".into(),
+            latches: true,
+            looks_locked_from: vec![],
+        };
+        
+        let switch_again = Action::LockView {
+            lock: "ĄĘ".into(),
+            unlock: "locked".into(),
+            latches: true,
+            looks_locked_from: vec![],
+        };
+        
+        let submit = Action::Erase;
+
+        let view = View::new(vec![(
+            0.0,
+            Row::new(vec![
+                (
+                    0.0,
+                    make_button_with_state(
+                        "switch".into(),
+                        make_state_with_action(switch.clone())
+                    ),
+                ),
+                (
+                    1.0,
+                    make_button_with_state(
+                        "submit".into(),
+                        make_state_with_action(submit.clone())
+                    ),
+                ),
+            ]),
+        )]);
+
+        let mut layout = Layout {
+            current_view: "base".into(),
+            view_latched: LatchedState::Not,
+            keymaps: Vec::new(),
+            kind: ArrangementKind::Base,
+            pressed_keys: HashSet::new(),
+            margins: Margins {
+                top: 0.0,
+                left: 0.0,
+                right: 0.0,
+                bottom: 0.0,
+            },
+            views: hashmap! {
+                // All can use the same structure.
+                // Switching doesn't depend on the view shape
+                // as long as the switching button is present.
+                "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
+                "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
+                "ĄĘ".into() => (c::Point { x: 0.0, y: 0.0 }, view),
+            },
+        };        
+
+        // Latch twice, then Ąto-unlatch across 2 levels
+        layout.apply_view_transition(&switch);
+        println!("{:?}", layout.view_latched);
+        assert_eq!(&layout.current_view, "locked");
+        layout.apply_view_transition(&switch_again);
+        println!("{:?}", layout.view_latched);
+        assert_eq!(&layout.current_view, "ĄĘ");
+        layout.apply_view_transition(&submit);
+        println!("{:?}", layout.view_latched);
+        assert_eq!(&layout.current_view, "base");
+    }
+
     #[test]
     fn check_centering() {
         //    A B
@@ -1192,6 +1445,7 @@ mod test {
         ]);
         let layout = Layout {
             current_view: String::new(),
+            view_latched: LatchedState::Not,
             keymaps: Vec::new(),
             kind: ArrangementKind::Base,
             pressed_keys: HashSet::new(),

src/popover.h

@@ -1,9 +0,0 @@
-#ifndef POPOVER_H__
-#define POPOVER_H__
-
-#include <gtk/gtk.h>
-#include "eek/eek-keyboard.h"
-
-void squeek_popover_show(GtkWidget*, struct button_place);
-
-#endif