Show terminal size overlay (COLSxROWS) during resize (#2833)

Display a centered overlay showing columns x rows when the terminal
control is resized. The overlay auto-hides after 750ms of inactivity.

- Add ResizeOverlay Border element to TermControl.xaml
- Add ViewWidth() to ControlCore (matches existing ViewHeight())
- Show overlay in _SwapChainSizeChanged using SafeDispatcherTimer
- Use fmt::format for string formatting

Closes #2833

Author: sagarbhure-msft

src/cascadia/TerminalControl/ControlCore.cpp

@@ -1580,6 +1580,17 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         return _terminal->GetViewport().Height();
     }
 
+    // Function Description:
+    // - Gets the width of the terminal in columns. This is just the
+    //   width of the viewport.
+    // Return Value:
+    // - The width of the terminal in columns
+    int ControlCore::ViewWidth() const
+    {
+        const auto lock = _terminal->LockForReading();
+        return _terminal->GetViewport().Width();
+    }
+
     // Function Description:
     // - Gets the height of the terminal in lines of text. This includes the
     //   history AND the viewport.

src/cascadia/TerminalControl/ControlCore.h

@@ -172,6 +172,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         int ScrollOffset();
         int ViewHeight() const;
+        int ViewWidth() const;
         int BufferHeight() const;
 
         bool HasSelection() const;

src/cascadia/TerminalControl/TermControl.cpp

@@ -2458,6 +2458,26 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         {
             _automationPeer.UpdateControlBounds();
         }
+
+        // Show resize overlay with COLSxROWS
+        const auto coreImpl = winrt::get_self<ControlCore>(_core);
+        const auto cols = coreImpl->ViewWidth();
+        const auto rows = coreImpl->ViewHeight();
+        if (cols > 0 && rows > 0)
+        {
+            ResizeOverlayText().Text(fmt::format(FMT_COMPILE(L"{} \u00D7 {}"), cols, rows));
+            ResizeOverlay().Visibility(Visibility::Visible);
+
+            _resizeOverlayTimer.Interval(std::chrono::milliseconds(750));
+            _resizeOverlayTimer.Tick([weakThis = get_weak()](auto&&, auto&&) {
+                if (auto self = weakThis.get())
+                {
+                    self->ResizeOverlay().Visibility(Visibility::Collapsed);
+                    self->_resizeOverlayTimer.Stop();
+                }
+            });
+            _resizeOverlayTimer.Start();
+        }
     }
 
     // Method Description:

src/cascadia/TerminalControl/TermControl.h

@@ -316,6 +316,8 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         winrt::hstring _restorePath;
         bool _showMarksInScrollbar{ false };
 
+        SafeDispatcherTimer _resizeOverlayTimer;
+
         bool _isBackgroundLight{ false };
         bool _detached{ false };
         til::CoordType _searchScrollOffset = 0;

src/cascadia/TerminalControl/TermControl.xaml

@@ -1365,6 +1365,24 @@
 
         </Grid>
 
+        <!-- Resize overlay: shows COLSxROWS when terminal is resized -->
+        <Border x:Name="ResizeOverlay"
+                HorizontalAlignment="Center"
+                VerticalAlignment="Center"
+                Padding="16,8,16,8"
+                Background="{ThemeResource SystemControlBackgroundAltHighBrush}"
+                BorderBrush="{ThemeResource SystemAccentColor}"
+                BorderThickness="1"
+                CornerRadius="{ThemeResource OverlayCornerRadius}"
+                IsHitTestVisible="False"
+                Visibility="Collapsed">
+            <TextBlock x:Name="ResizeOverlayText"
+                       FontSize="18"
+                       FontWeight="SemiBold"
+                       Foreground="{ThemeResource SystemControlForegroundBaseHighBrush}"
+                       TextAlignment="Center" />
+        </Border>
+
         <Grid x:Name="RendererFailedNotice"
               HorizontalAlignment="Center"
               VerticalAlignment="Center"