Add selection marker overlays for keyboard selection (#10865)

## Summary of the Pull Request
This introduces a selection marker overlay that tells the user which endpoint is currently being moved by the keyboard. The selection markers are respect font size changes and `cursor` color.

## References
#715 - Keyboard Selection
#2840 - Keyboard Selection Spec
#5804 - Mark Mode Spec

## Detailed Description of the Pull Request / Additional comments
- `TermControl` layer:
   - Use a canvas (similar to the one used for hyperlinks) to be able to draw the selection markers.
   - If we are notified that the selection changed, update the selection markers appropriately.
   - `UpdateSelectionMarkersEventArgs` lets us distinguish between mouse and keyboard selections.  `ClearMarkers` is set to true in the following cases...
      1.  Mouse selection, via SetEndSelectionPoint
      2. `LeftClickOnTerminal`, pretty self-explanatory
      3. a selection created from searching for text
- `ControlCore` layer:
   - Responsible for notifying `TermControl` to update the selection markers when a selection has changed.
   - Transfers info (the selection endpoint positions and which endpoint we're moving) from the terminal core to the term control.
- `TerminalCore` layer:
   - Provides the viewport position of the selection endpoints.


## Validation Steps Performed
- mouse selection (w/ and w/out shift) --> no markers
- keyboard selection --> markers
- markers update appropriately when we pivot the selection
- markers scroll when you hit a boundary
- markers take the color of the cursor color setting
- markers are resized when the font size changes

src/cascadia/TerminalControl/ControlCore.cpp

@@ -421,7 +421,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             {
                 auto lock = _terminal->LockForWriting();
                 _terminal->SelectAll();
-                _renderer->TriggerSelection();
+                _updateSelection();
                 return true;
             }
 
@@ -430,15 +430,15 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             {
                 auto lock = _terminal->LockForWriting();
                 _terminal->UpdateSelection(updateSlnParams->first, updateSlnParams->second, modifiers);
-                _renderer->TriggerSelection();
+                _updateSelection();
                 return true;
             }
 
             // GH#8791 - don't dismiss selection if Windows key was also pressed as a key-combination.
             if (!modifiers.IsWinPressed())
             {
                 _terminal->ClearSelection();
-                _renderer->TriggerSelection();
+                _updateSelection();
             }
 
             // When there is a selection active, escape should clear it and NOT flow through
@@ -934,6 +934,31 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         _terminal->SetSelectionAnchor(position);
     }
 
+    // Method Description:
+    // - Retrieves selection metadata from Terminal necessary to draw the
+    //    selection markers.
+    // - Since all of this needs to be done under lock, it is more performant
+    //    to throw it all in a struct and pass it along.
+    Control::SelectionData ControlCore::SelectionInfo() const
+    {
+        auto lock = _terminal->LockForReading();
+        Control::SelectionData info;
+
+        const auto start{ _terminal->SelectionStartForRendering() };
+        info.StartPos = { start.X, start.Y };
+
+        const auto end{ _terminal->SelectionEndForRendering() };
+        info.EndPos = { end.X, end.Y };
+
+        info.MovingEnd = _terminal->MovingEnd();
+        info.MovingCursor = _terminal->MovingCursor();
+
+        const auto bufferSize{ _terminal->GetTextBuffer().GetSize() };
+        info.StartAtLeftBoundary = _terminal->GetSelectionAnchor().x == bufferSize.Left();
+        info.EndAtRightBoundary = _terminal->GetSelectionEnd().x == bufferSize.RightInclusive();
+        return info;
+    }
+
     // Method Description:
     // - Sets selection's end position to match supplied cursor position, e.g. while mouse dragging.
     // Arguments:
@@ -957,6 +982,10 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         // save location (for rendering) + render
         _terminal->SetSelectionEnd(terminalPosition);
         _renderer->TriggerSelection();
+
+        // this is used for mouse dragging,
+        // so hide the markers
+        _UpdateSelectionMarkersHandlers(*this, winrt::make<implementation::UpdateSelectionMarkersEventArgs>(true));
     }
 
     // Called when the Terminal wants to set something to the clipboard, i.e.
@@ -1018,7 +1047,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         if (!_settings->CopyOnSelect())
         {
             _terminal->ClearSelection();
-            _renderer->TriggerSelection();
+            _updateSelection();
         }
 
         // send data up for clipboard
@@ -1034,7 +1063,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     {
         auto lock = _terminal->LockForWriting();
         _terminal->SelectAll();
-        _renderer->TriggerSelection();
+        _updateSelection();
     }
 
     bool ControlCore::ToggleBlockSelection()
@@ -1044,6 +1073,9 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         {
             _terminal->SetBlockSelection(!_terminal->IsBlockSelection());
             _renderer->TriggerSelection();
+            // do not update the selection markers!
+            // if we were showing them, keep it that way.
+            // otherwise, continue to not show them
             return true;
         }
         return false;
@@ -1053,7 +1085,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     {
         auto lock = _terminal->LockForWriting();
         _terminal->ToggleMarkMode();
-        _renderer->TriggerSelection();
+        _updateSelection();
     }
 
     bool ControlCore::IsInMarkMode() const
@@ -1068,7 +1100,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     {
         _terminal->WritePastedText(hstr);
         _terminal->ClearSelection();
-        _renderer->TriggerSelection();
+        _updateSelection();
         _terminal->TrySnapOnInput();
     }
 
@@ -1389,6 +1421,10 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             _terminal->SetBlockSelection(false);
             search.Select();
             _renderer->TriggerSelection();
+
+            // this is used for search,
+            // so hide the markers
+            _UpdateSelectionMarkersHandlers(*this, winrt::make<implementation::UpdateSelectionMarkersEventArgs>(true));
         }
 
         // Raise a FoundMatch event, which the control will use to notify
@@ -1589,8 +1625,14 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             _terminal->MultiClickSelection(terminalPosition, mode);
             selectionNeedsToBeCopied = true;
         }
+        _updateSelection();
+    }
 
+    void ControlCore::_updateSelection()
+    {
         _renderer->TriggerSelection();
+        const bool clearMarkers{ !_terminal->IsSelectionActive() };
+        _UpdateSelectionMarkersHandlers(*this, winrt::make<implementation::UpdateSelectionMarkersEventArgs>(clearMarkers));
     }
 
     void ControlCore::AttachUiaEngine(::Microsoft::Console::Render::IRenderEngine* const pEngine)

src/cascadia/TerminalControl/ControlCore.h

@@ -159,6 +159,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         bool HasSelection() const;
         bool CopyOnSelect() const;
         Windows::Foundation::Collections::IVector<winrt::hstring> SelectedText(bool trimTrailingWhitespace) const;
+        Control::SelectionData SelectionInfo() const;
         void SetSelectionAnchor(const til::point position);
         void SetEndSelectionPoint(const til::point position);
 
@@ -214,6 +215,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         TYPED_EVENT(ReceivedOutput,            IInspectable, IInspectable);
         TYPED_EVENT(FoundMatch,                IInspectable, Control::FoundResultsArgs);
         TYPED_EVENT(ShowWindowChanged,         IInspectable, Control::ShowWindowArgs);
+        TYPED_EVENT(UpdateSelectionMarkers,    IInspectable, Control::UpdateSelectionMarkersEventArgs);
         // clang-format on
 
     private:
@@ -269,6 +271,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         bool _setFontSizeUnderLock(int fontSize);
         void _updateFont(const bool initialUpdate = false);
         void _refreshSizeUnderLock();
+        void _updateSelection();
 
         void _sendInputToConnection(std::wstring_view wstr);
 

src/cascadia/TerminalControl/ControlCore.idl

@@ -29,6 +29,16 @@ namespace Microsoft.Terminal.Control
         All
     };
 
+    struct SelectionData
+    {
+        Microsoft.Terminal.Core.Point StartPos;
+        Microsoft.Terminal.Core.Point EndPos;
+        Boolean MovingEnd;
+        Boolean MovingCursor;
+        Boolean StartAtLeftBoundary;
+        Boolean EndAtRightBoundary;
+    };
+
     [default_interface] runtimeclass ControlCore : ICoreState
     {
         ControlCore(IControlSettings settings,
@@ -90,6 +100,7 @@ namespace Microsoft.Terminal.Control
 
         Boolean HasSelection { get; };
         IVector<String> SelectedText(Boolean trimTrailingWhitespace);
+        SelectionData SelectionInfo { get; };
 
         String HoveredUriText { get; };
         Windows.Foundation.IReference<Microsoft.Terminal.Core.Point> HoveredCell { get; };
@@ -125,6 +136,7 @@ namespace Microsoft.Terminal.Control
         event Windows.Foundation.TypedEventHandler<Object, Object> ReceivedOutput;
         event Windows.Foundation.TypedEventHandler<Object, FoundResultsArgs> FoundMatch;
         event Windows.Foundation.TypedEventHandler<Object, ShowWindowArgs> ShowWindowChanged;
+        event Windows.Foundation.TypedEventHandler<Object, UpdateSelectionMarkersEventArgs> UpdateSelectionMarkers;
 
     };
 }

src/cascadia/TerminalControl/EventArgs.cpp

@@ -13,3 +13,4 @@
 #include "TransparencyChangedEventArgs.g.cpp"
 #include "FoundResultsArgs.g.cpp"
 #include "ShowWindowArgs.g.cpp"
+#include "UpdateSelectionMarkersEventArgs.g.cpp"

src/cascadia/TerminalControl/EventArgs.h

@@ -13,6 +13,7 @@
 #include "TransparencyChangedEventArgs.g.h"
 #include "FoundResultsArgs.g.h"
 #include "ShowWindowArgs.g.h"
+#include "UpdateSelectionMarkersEventArgs.g.h"
 
 namespace winrt::Microsoft::Terminal::Control::implementation
 {
@@ -157,4 +158,15 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         WINRT_PROPERTY(bool, ShowOrHide);
     };
+
+    struct UpdateSelectionMarkersEventArgs : public UpdateSelectionMarkersEventArgsT<UpdateSelectionMarkersEventArgs>
+    {
+    public:
+        UpdateSelectionMarkersEventArgs(const bool clearMarkers) :
+            _ClearMarkers(clearMarkers)
+        {
+        }
+
+        WINRT_PROPERTY(bool, ClearMarkers, false);
+    };
 }

src/cascadia/TerminalControl/EventArgs.idl

@@ -69,7 +69,6 @@ namespace Microsoft.Terminal.Control
         Double Opacity { get; };
     }
 
-
     runtimeclass FoundResultsArgs
     {
         Boolean FoundMatch { get; };
@@ -79,4 +78,9 @@ namespace Microsoft.Terminal.Control
     {
         Boolean ShowOrHide { get; };
     }
+
+    runtimeclass UpdateSelectionMarkersEventArgs
+    {
+        Boolean ClearMarkers { get; };
+    }
 }