Add support for moving focus between panes with the keyboard (#1910)

Enables the user to set keybindings to move focus between panes with the keyboard. 
This is highly based off the work done for resizing panes. Same logic applies - 
  moving focus will move up the panes tree until we find a pane to move the focus to.

src/cascadia/TerminalApp/App.cpp

@@ -505,6 +505,7 @@ namespace winrt::TerminalApp::implementation
         bindings.SwitchToTab([this](const auto index) { _SelectTab({ index }); });
         bindings.OpenSettings([this]() { _OpenSettings(); });
         bindings.ResizePane([this](const auto direction) { _ResizePane(direction); });
+        bindings.MoveFocus([this](const auto direction) { _MoveFocus(direction); });
         bindings.CopyText([this](const auto trimWhitespace) { _CopyText(trimWhitespace); });
         bindings.PasteText([this]() { _PasteText(); });
     }
@@ -1028,6 +1029,20 @@ namespace winrt::TerminalApp::implementation
         _tabs[focusedTabIndex]->ResizePane(direction);
     }
 
+    // Method Description:
+    // - Attempt to move focus between panes, as to focus the child on
+    //   the other side of the separator. See Pane::NavigateFocus for details.
+    // - Moves the focus of the currently focused tab.
+    // Arguments:
+    // - direction: The direction to move the focus in.
+    // Return Value:
+    // - <none>
+    void App::_MoveFocus(const Direction& direction)
+    {
+        const auto focusedTabIndex = _GetFocusedTabIndex();
+        _tabs[focusedTabIndex]->NavigateFocus(direction);
+    }
+
     // Method Description:
     // - Copy text from the focused terminal to the Windows Clipboard
     // Arguments:

src/cascadia/TerminalApp/App.h

@@ -122,6 +122,7 @@ namespace winrt::TerminalApp::implementation
         // MSFT:20641986: Add keybindings for New Window
         void _ScrollPage(int delta);
         void _ResizePane(const Direction& direction);
+        void _MoveFocus(const Direction& direction);
 
         void _OnLoaded(const IInspectable& sender, const Windows::UI::Xaml::RoutedEventArgs& eventArgs);
         void _OnTabSelectionChanged(const IInspectable& sender, const Windows::UI::Xaml::Controls::SelectionChangedEventArgs& eventArgs);

src/cascadia/TerminalApp/AppKeyBindings.cpp

@@ -169,7 +169,18 @@ namespace winrt::TerminalApp::implementation
         case ShortcutAction::ResizePaneDown:
             _ResizePaneHandlers(Direction::Down);
             return true;
-
+        case ShortcutAction::MoveFocusLeft:
+            _MoveFocusHandlers(Direction::Left);
+            return true;
+        case ShortcutAction::MoveFocusRight:
+            _MoveFocusHandlers(Direction::Right);
+            return true;
+        case ShortcutAction::MoveFocusUp:
+            _MoveFocusHandlers(Direction::Up);
+            return true;
+        case ShortcutAction::MoveFocusDown:
+            _MoveFocusHandlers(Direction::Down);
+            return true;
         default:
             return false;
         }
@@ -251,5 +262,6 @@ namespace winrt::TerminalApp::implementation
     DEFINE_EVENT(AppKeyBindings, ScrollDownPage,    _ScrollDownPageHandlers,    TerminalApp::ScrollDownPageEventArgs);
     DEFINE_EVENT(AppKeyBindings, OpenSettings,      _OpenSettingsHandlers,      TerminalApp::OpenSettingsEventArgs);
     DEFINE_EVENT(AppKeyBindings, ResizePane,        _ResizePaneHandlers,        TerminalApp::ResizePaneEventArgs);
+    DEFINE_EVENT(AppKeyBindings, MoveFocus,         _MoveFocusHandlers,         TerminalApp::MoveFocusEventArgs);
     // clang-format on
 }

src/cascadia/TerminalApp/AppKeyBindings.h

@@ -61,6 +61,7 @@ namespace winrt::TerminalApp::implementation
         DECLARE_EVENT(ScrollDownPage,    _ScrollDownPageHandlers,    TerminalApp::ScrollDownPageEventArgs);
         DECLARE_EVENT(OpenSettings,      _OpenSettingsHandlers,      TerminalApp::OpenSettingsEventArgs);
         DECLARE_EVENT(ResizePane,        _ResizePaneHandlers,        TerminalApp::ResizePaneEventArgs);
+        DECLARE_EVENT(MoveFocus,         _MoveFocusHandlers,         TerminalApp::MoveFocusEventArgs);
         // clang-format on
 
     private:

src/cascadia/TerminalApp/AppKeyBindings.idl

@@ -53,6 +53,10 @@ namespace TerminalApp
         ResizePaneRight,
         ResizePaneUp,
         ResizePaneDown,
+        MoveFocusLeft,
+        MoveFocusRight,
+        MoveFocusUp,
+        MoveFocusDown,
         OpenSettings
     };
 
@@ -77,9 +81,9 @@ namespace TerminalApp
     delegate void ScrollDownPageEventArgs();
     delegate void OpenSettingsEventArgs();
     delegate void ResizePaneEventArgs(Direction direction);
+    delegate void MoveFocusEventArgs(Direction direction);
 
-    [default_interface]
-    runtimeclass AppKeyBindings : Microsoft.Terminal.Settings.IKeyBindings
+    [default_interface] runtimeclass AppKeyBindings : Microsoft.Terminal.Settings.IKeyBindings
     {
         AppKeyBindings();
 
@@ -107,5 +111,6 @@ namespace TerminalApp
         event ScrollDownPageEventArgs ScrollDownPage;
         event OpenSettingsEventArgs OpenSettings;
         event ResizePaneEventArgs ResizePane;
+        event MoveFocusEventArgs MoveFocus;
     }
 }

src/cascadia/TerminalApp/AppKeyBindingsSerialization.cpp

@@ -55,6 +55,10 @@ static constexpr std::string_view ResizePaneLeftKey{ "resizePaneLeft" };
 static constexpr std::string_view ResizePaneRightKey{ "resizePaneRight" };
 static constexpr std::string_view ResizePaneUpKey{ "resizePaneUp" };
 static constexpr std::string_view ResizePaneDownKey{ "resizePaneDown" };
+static constexpr std::string_view MoveFocusLeftKey{ "moveFocusLeft" };
+static constexpr std::string_view MoveFocusRightKey{ "moveFocusRight" };
+static constexpr std::string_view MoveFocusUpKey{ "moveFocusUp" };
+static constexpr std::string_view MoveFocusDownKey{ "moveFocusDown" };
 
 // Specifically use a map here over an unordered_map. We want to be able to
 // iterate over these entries in-order when we're serializing the keybindings.
@@ -105,6 +109,10 @@ static const std::map<std::string_view, ShortcutAction, std::less<>> commandName
     { ResizePaneRightKey, ShortcutAction::ResizePaneRight },
     { ResizePaneUpKey, ShortcutAction::ResizePaneUp },
     { ResizePaneDownKey, ShortcutAction::ResizePaneDown },
+    { MoveFocusLeftKey, ShortcutAction::MoveFocusLeft },
+    { MoveFocusRightKey, ShortcutAction::MoveFocusRight },
+    { MoveFocusUpKey, ShortcutAction::MoveFocusUp },
+    { MoveFocusDownKey, ShortcutAction::MoveFocusDown },
     { OpenSettingsKey, ShortcutAction::OpenSettings },
 };
 

src/cascadia/TerminalApp/Pane.cpp

@@ -187,6 +187,95 @@ bool Pane::ResizePane(const Direction& direction)
     return false;
 }
 
+// Method Description:
+// - Attempts to handle moving focus to one of our children. If our split
+//   direction isn't appropriate for the move direction, then we'll return
+//   false, to try and let our parent handle the move. If our child we'd move
+//   focus to is already focused, we'll also return false, to again let our
+//   parent try and handle the focus movement.
+// Arguments:
+// - direction: The direction to move the focus in.
+// Return Value:
+// - true if we handled this focus move request.
+bool Pane::_NavigateFocus(const Direction& direction)
+{
+    if (!DirectionMatchesSplit(direction, _splitState))
+    {
+        return false;
+    }
+
+    const bool focusSecond = (direction == Direction::Right) || (direction == Direction::Down);
+
+    const auto newlyFocusedChild = focusSecond ? _secondChild : _firstChild;
+
+    // If the child we want to move focus to is _already_ focused, return false,
+    // to try and let our parent figure it out.
+    if (newlyFocusedChild->WasLastFocused())
+    {
+        return false;
+    }
+
+    // Transfer focus to our child, and update the focus of our tree.
+    newlyFocusedChild->_FocusFirstChild();
+    UpdateFocus();
+
+    return true;
+}
+
+// Method Description:
+// - Attempts to move focus to one of our children. If we have a focused child,
+//   we'll try to move the focus in the direction requested.
+//   - If there isn't a pane that exists as a child of this pane in the correct
+//     direction, we'll return false. This will indicate to our parent that they
+//     should try and move the focus themselves. In this way, the focus can move
+//     up and down the tree to the correct pane.
+// - This method is _very_ similar to ResizePane. Both are trying to find the
+//   right separator to move (focus) in a direction.
+// Arguments:
+// - direction: The direction to move the focus in.
+// Return Value:
+// - true if we or a child handled this focus move request.
+bool Pane::NavigateFocus(const Direction& direction)
+{
+    // If we're a leaf, do nothing. We can't possibly have a descendant with a
+    // separator the correct direction.
+    if (_IsLeaf())
+    {
+        return false;
+    }
+
+    // Check if either our first or second child is the currently focused leaf.
+    // If it is, and the requested move direction matches our separator, then
+    // we're the pane that needs to handle this focus move.
+    const bool firstIsFocused = _firstChild->_IsLeaf() && _firstChild->_lastFocused;
+    const bool secondIsFocused = _secondChild->_IsLeaf() && _secondChild->_lastFocused;
+    if (firstIsFocused || secondIsFocused)
+    {
+        return _NavigateFocus(direction);
+    }
+    else
+    {
+        // If neither of our children were the focused leaf, then recurse into
+        // our children and see if they can handle the focus move.
+        // For each child, if it has a focused descendant, try having that child
+        // handle the focus move.
+        // If the child wasn't able to handle the focus move, it's possible that
+        // there were no descendants with a separator the correct direction. If
+        // our separator _is_ the correct direction, then we should be the pane
+        // to move focus into our other child. Otherwise, just return false, as
+        // we couldn't handle it either.
+        if ((!_firstChild->_IsLeaf()) && _firstChild->_HasFocusedChild())
+        {
+            return _firstChild->NavigateFocus(direction) || _NavigateFocus(direction);
+        }
+        else if ((!_secondChild->_IsLeaf()) && _secondChild->_HasFocusedChild())
+        {
+            return _secondChild->NavigateFocus(direction) || _NavigateFocus(direction);
+        }
+    }
+    return false;
+}
+
 // Method Description:
 // - Called when our attached control is closed. Triggers listeners to our close
 //   event, if we're a leaf pane.

src/cascadia/TerminalApp/Pane.h

@@ -47,6 +47,7 @@ class Pane : public std::enable_shared_from_this<Pane>
     void UpdateSettings(const winrt::Microsoft::Terminal::Settings::TerminalSettings& settings, const GUID& profile);
     void ResizeContent(const winrt::Windows::Foundation::Size& newSize);
     bool ResizePane(const winrt::TerminalApp::Direction& direction);
+    bool NavigateFocus(const winrt::TerminalApp::Direction& direction);
 
     void SplitHorizontal(const GUID& profile, const winrt::Microsoft::Terminal::TerminalControl::TermControl& control);
     void SplitVertical(const GUID& profile, const winrt::Microsoft::Terminal::TerminalControl::TermControl& control);
@@ -80,7 +81,9 @@ class Pane : public std::enable_shared_from_this<Pane>
     void _CreateRowColDefinitions(const winrt::Windows::Foundation::Size& rootSize);
     void _CreateSplitContent();
     void _ApplySplitDefinitions();
+
     bool _Resize(const winrt::TerminalApp::Direction& direction);
+    bool _NavigateFocus(const winrt::TerminalApp::Direction& direction);
 
     void _CloseChild(const bool closeFirst);
 

src/cascadia/TerminalApp/Tab.cpp

@@ -237,4 +237,16 @@ void Tab::ResizePane(const winrt::TerminalApp::Direction& direction)
     _rootPane->ResizePane(direction);
 }
 
+// Method Description:
+// - Attempt to move focus between panes, as to focus the child on
+//   the other side of the separator. See Pane::NavigateFocus for details.
+// Arguments:
+// - direction: The direction to move the focus in.
+// Return Value:
+// - <none>
+void Tab::NavigateFocus(const winrt::TerminalApp::Direction& direction)
+{
+    _rootPane->NavigateFocus(direction);
+}
+
 DEFINE_EVENT(Tab, Closed, _closedHandlers, ConnectionClosedEventArgs);

src/cascadia/TerminalApp/Tab.h

@@ -25,6 +25,7 @@ class Tab
     void UpdateFocus();
     void ResizeContent(const winrt::Windows::Foundation::Size& newSize);
     void ResizePane(const winrt::TerminalApp::Direction& direction);
+    void NavigateFocus(const winrt::TerminalApp::Direction& direction);
 
     void UpdateSettings(const winrt::Microsoft::Terminal::Settings::TerminalSettings& settings, const GUID& profile);
     winrt::hstring GetFocusedTitle() const;