Show a double width cursor for double width characters

src/buffer/out/textBuffer.cpp

@@ -1967,11 +1967,8 @@ HRESULT TextBuffer::Reflow(TextBuffer& oldBuffer,
                            const std::optional<Viewport> lastCharacterViewport,
                            std::optional<std::reference_wrapper<PositionInformation>> positionInfo)
 {
-    Cursor& oldCursor = oldBuffer.GetCursor();
+    const Cursor& oldCursor = oldBuffer.GetCursor();
     Cursor& newCursor = newBuffer.GetCursor();
-    // skip any drawing updates that might occur as we manipulate the new buffer
-    oldCursor.StartDeferDrawing();
-    newCursor.StartDeferDrawing();
 
     // We need to save the old cursor position so that we can
     // place the new cursor back on the equivalent character in
@@ -2197,8 +2194,5 @@ HRESULT TextBuffer::Reflow(TextBuffer& oldBuffer,
         newCursor.SetSize(ulSize);
     }
 
-    newCursor.EndDeferDrawing();
-    oldCursor.EndDeferDrawing();
-
     return hr;
 }

src/cascadia/TerminalCore/Terminal.cpp

@@ -199,6 +199,10 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
                                                      0, // temporarily set size to 0 so it won't render.
                                                      _buffer->GetRenderTarget());
 
+        // skip any drawing updates that might occur as we manipulate the new buffer, until we swap the new with the old.
+        _buffer->GetCursor().StartDeferDrawing();
+        newTextBuffer->GetCursor().StartDeferDrawing();
+
         // Build a PositionInformation to track the position of both the top of
         // the mutable viewport and the top of the visible viewport in the new
         // buffer.
@@ -222,7 +226,11 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
         newViewportTop = oldRows.mutableViewportTop;
         newVisibleTop = oldRows.visibleViewportTop;
     }
-    CATCH_RETURN();
+    catch (...)
+    {
+        _buffer->GetCursor().EndDeferDrawing();
+        RETURN_CAUGHT_EXCEPTION();
+    }
 
     // Conpty resizes a little oddly - if the height decreased, and there were
     // blank lines at the bottom, those lines will get trimmed. If there's not
@@ -329,6 +337,9 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 
     _buffer.swap(newTextBuffer);
 
+    // Now that the new buffer was swapped to be Terminal's buffer, we can tell its cursor to start drawing again.
+    _buffer->GetCursor().EndDeferDrawing();
+
     // GH#3494: Maintain scrollbar position during resize
     // Make sure that we don't scroll past the mutableViewport at the bottom of the buffer
     newVisibleTop = std::min(newVisibleTop, _mutableViewport.Top());
@@ -877,6 +888,7 @@ CATCH_LOG()
 // - isVisible: whether the cursor should be visible
 void Terminal::SetCursorOn(const bool isOn) noexcept
 {
+    auto lock = LockForWriting();
     _buffer->GetCursor().SetIsOn(isOn);
 }
 

src/cascadia/TerminalCore/Terminal.hpp

@@ -11,6 +11,7 @@
 #include "../../terminal/input/terminalInput.hpp"
 
 #include "../../types/inc/Viewport.hpp"
+#include "../../types/inc/GlyphWidth.hpp"
 #include "../../types/IUiaData.h"
 #include "../../cascadia/terminalcore/ITerminalApi.hpp"
 #include "../../cascadia/terminalcore/ITerminalInput.hpp"

src/cascadia/TerminalCore/terminalrenderdata.cpp

@@ -107,7 +107,9 @@ COLORREF Terminal::GetCursorColor() const noexcept
 
 bool Terminal::IsCursorDoubleWidth() const noexcept
 {
-    return false;
+    const auto position = _buffer->GetCursor().GetPosition();
+    TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
+    return IsGlyphFullWidth(*it);
 }
 
 const std::vector<RenderOverlay> Terminal::GetOverlays() const noexcept

src/cascadia/UnitTests_TerminalCore/TerminalApiTest.cpp

@@ -33,6 +33,7 @@ namespace TerminalCoreUnitTests
         // This test ensures that Terminal::_WriteBuffer doesn't get stuck when
         // PrintString() is called with more code units than the buffer width.
         TEST_METHOD(PrintStringOfSurrogatePairs);
+        TEST_METHOD(CheckDoubleWidthCursor);
     };
 };
 
@@ -208,3 +209,45 @@ void TerminalApiTest::CursorVisibilityViaStateMachine()
     VERIFY_IS_FALSE(cursor.IsBlinkingAllowed());
     VERIFY_IS_FALSE(cursor.IsVisible());
 }
+
+void TerminalApiTest::CheckDoubleWidthCursor()
+{
+    DummyRenderTarget renderTarget;
+    Terminal term;
+    term.Create({ 100, 100 }, 0, renderTarget);
+
+    auto& tbi = *(term._buffer);
+    auto& stateMachine = *(term._stateMachine);
+    auto& cursor = tbi.GetCursor();
+
+    // Lets stuff the buffer with single width characters,
+    // but leave the last two columns empty for double width.
+    std::wstring singleWidthText;
+    singleWidthText.reserve(98);
+    for (size_t i = 0; i < 98; ++i)
+    {
+        singleWidthText.append(L"A");
+    }
+    stateMachine.ProcessString(singleWidthText);
+    VERIFY_IS_TRUE(cursor.GetPosition().X == 98);
+
+    // Stuff two double width characters.
+    std::wstring doubleWidthText{ L"我愛" };
+    stateMachine.ProcessString(doubleWidthText);
+
+    // The last 'A'
+    term.SetCursorPosition(97, 0);
+    VERIFY_IS_FALSE(term.IsCursorDoubleWidth());
+
+    // This and the next CursorPos are taken up by '我‘
+    term.SetCursorPosition(98, 0);
+    VERIFY_IS_TRUE(term.IsCursorDoubleWidth());
+    term.SetCursorPosition(99, 0);
+    VERIFY_IS_TRUE(term.IsCursorDoubleWidth());
+
+    // This and the next CursorPos are taken up by ’愛‘
+    term.SetCursorPosition(0, 1);
+    VERIFY_IS_TRUE(term.IsCursorDoubleWidth());
+    term.SetCursorPosition(1, 1);
+    VERIFY_IS_TRUE(term.IsCursorDoubleWidth());
+}

src/host/screenInfo.cpp

@@ -1403,6 +1403,10 @@ bool SCREEN_INFORMATION::IsMaximizedY() const
     // Save cursor's relative height versus the viewport
     SHORT const sCursorHeightInViewportBefore = _textBuffer->GetCursor().GetPosition().Y - _viewport.Top();
 
+    // Tell the both the new and old buffer to not redraw its cursor as we reflow and swap them.
+    newTextBuffer->GetCursor().StartDeferDrawing();
+    _textBuffer->GetCursor().StartDeferDrawing();
+
     HRESULT hr = TextBuffer::Reflow(*_textBuffer.get(), *newTextBuffer.get(), std::nullopt, std::nullopt);
 
     if (SUCCEEDED(hr))
@@ -1417,6 +1421,10 @@ bool SCREEN_INFORMATION::IsMaximizedY() const
         _textBuffer.swap(newTextBuffer);
     }
 
+    // Only tell _textBuffer to EndDefer (and not newTextBuffer) because whether or not Reflow failed,
+    // _textBuffer will end up being the buffer that we use after returning.
+    _textBuffer->GetCursor().EndDeferDrawing();
+
     return NTSTATUS_FROM_HRESULT(hr);
 }