From a2dc867dfa906cff66da3e804c2085b9a162a9d8 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 31 Mar 2020 14:08:12 -0700
Subject: [PATCH 01/18] first lets add back the code that crashes

---
 src/cascadia/TerminalCore/Terminal.hpp           | 1 +
 src/cascadia/TerminalCore/terminalrenderdata.cpp | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/cascadia/TerminalCore/Terminal.hpp b/src/cascadia/TerminalCore/Terminal.hpp
index f5ca256e31a..f10bd4ba9b4 100644
--- a/src/cascadia/TerminalCore/Terminal.hpp
+++ b/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"
diff --git a/src/cascadia/TerminalCore/terminalrenderdata.cpp b/src/cascadia/TerminalCore/terminalrenderdata.cpp
index e49859cb374..686b2334575 100644
--- a/src/cascadia/TerminalCore/terminalrenderdata.cpp
+++ b/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

From 56392f62befa024693ec6156e4bcf042598fc12b Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Thu, 2 Apr 2020 13:41:12 -0700
Subject: [PATCH 02/18] adding a test that may or may not work

---
 src/cascadia/TerminalCore/Terminal.cpp |  2 +
 src/host/ft_host/API_OutputTests.cpp   | 56 +++++++++++++++++++++++++-
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index b3471ee68eb..a73436fb0e0 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -683,6 +683,8 @@ void Terminal::_AdjustCursorPosition(const COORD proposedPosition)
         notifyScroll = true;
     }
 
+    proposedCursorPosition.X = base::ClampMin(proposedCursorPosition.X, ::base::ClampedNumeric<short>(bufferSize.Width() - 1));
+
     // Update Cursor Position
     cursor.SetPosition(proposedCursorPosition);
 
diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index 4912f17a597..bed09cfd605 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
 #include "precomp.h"
@@ -46,6 +46,8 @@ class OutputTests
     TEST_METHOD(WriteBackspaceTest);
 
     TEST_METHOD(WinPtyWrite);
+
+    TEST_METHOD(WriteTwoColumnCharacterToCheckOverflow);
 };
 
 bool OutputTests::TestSetup()
@@ -1062,3 +1064,55 @@ void OutputTests::WinPtyWrite()
         break;
     }
 }
+
+void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
+{
+    // Get output buffer information.
+    const auto consoleOutputHandle = GetStdOutputHandle();
+    SetConsoleActiveScreenBuffer(consoleOutputHandle);
+
+    CONSOLE_SCREEN_BUFFER_INFOEX sbiex{ 0 };
+    sbiex.cbSize = sizeof(sbiex);
+
+    VERIFY_WIN32_BOOL_SUCCEEDED(GetConsoleScreenBufferInfoEx(consoleOutputHandle, &sbiex));
+    const auto bufferSize = sbiex.dwSize;
+
+    // Establish a writing region that is the width of the buffer and half the height.
+    const SMALL_RECT region{ 0, 0, bufferSize.X - 1, 1 };
+    const COORD regionDimensions{ region.Right - region.Left + 1, region.Bottom - region.Top + 1 };
+    const auto regionSize = regionDimensions.X * regionDimensions.Y;
+    const COORD regionOrigin{ 0, 0 };
+
+    // Make a double width character value with lead bit and fill an array (via a vector) full of it.
+    // We just want the character to be in the last column of the buffer.
+    CHAR_INFO testValue;
+    testValue.Attributes = 0x0100;
+    testValue.Char.UnicodeChar = L'是';
+
+    std::vector<CHAR_INFO> buffer(regionSize, testValue);
+
+    CHAR_INFO lastColumnValue;
+    lastColumnValue.Attributes = 0x0100;
+    lastColumnValue.Char.UnicodeChar = L'我';
+    buffer[regionSize - 1] = lastColumnValue;
+
+    // Call the API and confirm results.
+    SMALL_RECT affected = region;
+    VERIFY_WIN32_BOOL_SUCCEEDED(WriteConsoleOutputW(consoleOutputHandle, buffer.data(), regionDimensions, regionOrigin, &affected));
+    VERIFY_ARE_EQUAL(region, affected);
+
+    // Move the cursor to the last column of the buffer
+    VERIFY_WIN32_BOOL_SUCCEEDED(SetConsoleCursorPosition(consoleOutputHandle, { bufferSize.X - 1, 0 }));
+
+    // Check that the character
+    const auto cursorPos = sbiex.dwCursorPosition;
+
+    // Make an array that can hold the output
+    std::vector<CHAR_INFO> singleBuf(1);
+
+    // Call the API and confirm results
+    SMALL_RECT singleAffectedRegion = { 0, 0, 1, 1 };
+    const COORD singleRegionDimension = { 1, 1 };
+    VERIFY_WIN32_BOOL_SUCCEEDED(ReadConsoleOutputW(consoleOutputHandle, singleBuf.data(), singleRegionDimension, cursorPos, &affected));
+    VERIFY_ARE_EQUAL(singleBuf[0], lastColumnValue);
+}

From b86d85ed72366a26ae6bef09321ee9dbb2497bcb Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Fri, 3 Apr 2020 01:59:30 -0700
Subject: [PATCH 03/18] test case

---
 src/cascadia/TerminalCore/Terminal.cpp |  2 +-
 src/host/ft_host/API_OutputTests.cpp   | 36 ++++++++++++++------------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index a73436fb0e0..37fd13c639f 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -683,7 +683,7 @@ void Terminal::_AdjustCursorPosition(const COORD proposedPosition)
         notifyScroll = true;
     }
 
-    proposedCursorPosition.X = base::ClampMin(proposedCursorPosition.X, ::base::ClampedNumeric<short>(bufferSize.Width() - 1));
+    //proposedCursorPosition.X = base::ClampMin(proposedCursorPosition.X, ::base::ClampedNumeric<short>(bufferSize.Width() - 1));
 
     // Update Cursor Position
     cursor.SetPosition(proposedCursorPosition);
diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index bed09cfd605..499eab10b7f 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -1078,21 +1078,20 @@ void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
     const auto bufferSize = sbiex.dwSize;
 
     // Establish a writing region that is the width of the buffer and half the height.
-    const SMALL_RECT region{ 0, 0, bufferSize.X - 1, 1 };
+    const SMALL_RECT region{ 0, 0, bufferSize.X - 1, 0 };
     const COORD regionDimensions{ region.Right - region.Left + 1, region.Bottom - region.Top + 1 };
     const auto regionSize = regionDimensions.X * regionDimensions.Y;
     const COORD regionOrigin{ 0, 0 };
 
-    // Make a double width character value with lead bit and fill an array (via a vector) full of it.
-    // We just want the character to be in the last column of the buffer.
     CHAR_INFO testValue;
-    testValue.Attributes = 0x0100;
-    testValue.Char.UnicodeChar = L'是';
+    testValue.Attributes = 0x3e;
+    testValue.Char.UnicodeChar = L'A';
 
     std::vector<CHAR_INFO> buffer(regionSize, testValue);
 
+    // Place a double width character with a lead bit in the last column of the buffer.
     CHAR_INFO lastColumnValue;
-    lastColumnValue.Attributes = 0x0100;
+    lastColumnValue.Attributes = 0x13e;
     lastColumnValue.Char.UnicodeChar = L'我';
     buffer[regionSize - 1] = lastColumnValue;
 
@@ -1104,15 +1103,18 @@ void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
     // Move the cursor to the last column of the buffer
     VERIFY_WIN32_BOOL_SUCCEEDED(SetConsoleCursorPosition(consoleOutputHandle, { bufferSize.X - 1, 0 }));
 
-    // Check that the character
-    const auto cursorPos = sbiex.dwCursorPosition;
-
-    // Make an array that can hold the output
-    std::vector<CHAR_INFO> singleBuf(1);
-
-    // Call the API and confirm results
-    SMALL_RECT singleAffectedRegion = { 0, 0, 1, 1 };
-    const COORD singleRegionDimension = { 1, 1 };
-    VERIFY_WIN32_BOOL_SUCCEEDED(ReadConsoleOutputW(consoleOutputHandle, singleBuf.data(), singleRegionDimension, cursorPos, &affected));
-    VERIFY_ARE_EQUAL(singleBuf[0], lastColumnValue);
+    //// Make an array that can hold the output
+    //std::vector<CHAR_INFO> readBuffer(regionSize);
+
+    //// Call the API and confirm results
+    //SMALL_RECT readRegion = region;
+    //VERIFY_WIN32_BOOL_SUCCEEDED(ReadConsoleOutputW(consoleOutputHandle, readBuffer.data(), regionDimensions, regionOrigin, &readRegion));
+    //for (auto x : readBuffer)
+    //{
+    //    for (int i = 0; i < 1000; ++i)
+    //    {
+    //        VERIFY_ARE_EQUAL(x, testValue);
+    //    }
+    //    
+    //}
 }

From 9e149cbfe56239eaed8b2a3ecb3f840f0c1b8457 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 7 Apr 2020 14:45:26 -0700
Subject: [PATCH 04/18] i just add debug for now

---
 src/cascadia/TerminalCore/Terminal.cpp | 22 ++++++++++++++++++++--
 src/renderer/base/renderer.cpp         |  4 ++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 37fd13c639f..d88487c8d1c 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -165,6 +165,12 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 [[nodiscard]] HRESULT Terminal::UserResize(const COORD viewportSize) noexcept
 {
     const auto oldDimensions = _mutableViewport.Dimensions();
+
+    if (!_buffer->GetSize().IsInBounds(_buffer->GetCursor().GetPosition()))
+    {
+        OutputDebugString(L"UserResize not in bounds\n");
+    }   
+
     if (viewportSize == oldDimensions)
     {
         return S_FALSE;
@@ -630,6 +636,12 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             // If "wch" was a surrogate character, we just consumed 2 code units above.
             // -> Increment "i" by 1 in that case and thus by 2 in total in this iteration.
             proposedCursorPosition.X += gsl::narrow<SHORT>(cellDistance);
+
+            if (!_buffer->GetSize().IsInBounds(proposedCursorPosition))
+            {
+                OutputDebugString(L"InDist > 0 not in Bounds\n");
+            }
+
             i += inputDistance - 1;
         }
         else
@@ -646,6 +658,8 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             // Try the character again.
             i--;
 
+            OutputDebugString(L"Reset to 0\n");
+
             // If we write the last cell of the row here, TextBuffer::Write will
             // mark this line as wrapped for us. If the next character we
             // process is a newline, the Terminal::CursorLineFeed will unmark
@@ -660,6 +674,11 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
         _AdjustCursorPosition(proposedCursorPosition);
     }
 
+    if (!_buffer->GetSize().IsInBounds(_buffer->GetCursor().GetPosition()))
+    {
+        OutputDebugString(L"Still not in Bounds\n");
+    }
+
     cursor.EndDeferDrawing();
 }
 
@@ -683,8 +702,6 @@ void Terminal::_AdjustCursorPosition(const COORD proposedPosition)
         notifyScroll = true;
     }
 
-    //proposedCursorPosition.X = base::ClampMin(proposedCursorPosition.X, ::base::ClampedNumeric<short>(bufferSize.Width() - 1));
-
     // Update Cursor Position
     cursor.SetPosition(proposedCursorPosition);
 
@@ -800,6 +817,7 @@ CATCH_LOG()
 // - isVisible: whether the cursor should be visible
 void Terminal::SetCursorOn(const bool isOn) noexcept
 {
+    auto lock = LockForWriting();
     _buffer->GetCursor().SetIsOn(isOn);
 }
 
diff --git a/src/renderer/base/renderer.cpp b/src/renderer/base/renderer.cpp
index dfe4bdd3a6d..ef293999c5c 100644
--- a/src/renderer/base/renderer.cpp
+++ b/src/renderer/base/renderer.cpp
@@ -832,6 +832,10 @@ void Renderer::_PaintCursor(_In_ IRenderEngine* const pEngine)
             // Draw it within the viewport
             LOG_IF_FAILED(pEngine->PaintCursor(options));
         }
+        else
+        {
+            OutputDebugString(L"PaintCursor NOT In Bounds \n");
+        }
     }
 }
 

From 5fcbac7a3505240cc2d4c30e833e181a1dcf0596 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Wed, 8 Apr 2020 15:14:30 -0700
Subject: [PATCH 05/18] mAYBE

---
 src/buffer/out/cursor.cpp              | 19 +++++++++-----
 src/buffer/out/cursor.h                |  1 +
 src/cascadia/TerminalCore/Terminal.cpp | 36 ++++++++++++++------------
 src/renderer/base/renderer.cpp         | 11 +++++---
 4 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/src/buffer/out/cursor.cpp b/src/buffer/out/cursor.cpp
index 46f0208f820..359a3eb43d1 100644
--- a/src/buffer/out/cursor.cpp
+++ b/src/buffer/out/cursor.cpp
@@ -29,7 +29,8 @@ Cursor::Cursor(const ULONG ulSize, TextBuffer& parentBuffer) noexcept :
     _ulSize(ulSize),
     _cursorType(CursorType::Legacy),
     _fUseColor(false),
-    _color(s_InvertCursorColor)
+    _color(s_InvertCursorColor),
+    _iDeferCounter{ 0 }
 {
 }
 
@@ -166,7 +167,7 @@ void Cursor::_RedrawCursor() noexcept
     // (Conversion areas have cursors to mark the insertion point internally, but the user's actual cursor is the one on the primary screen buffer.)
     if (IsOn() && !IsConversionArea())
     {
-        if (_fDeferCursorRedraw)
+        if (_iDeferCounter > 0)
         {
             _fHaveDeferredCursorRedraw = true;
         }
@@ -281,6 +282,7 @@ void Cursor::CopyProperties(const Cursor& OtherCursor) noexcept
 
     _fDeferCursorRedraw = OtherCursor._fDeferCursorRedraw;
     _fHaveDeferredCursorRedraw = OtherCursor._fHaveDeferredCursorRedraw;
+    _iDeferCounter = OtherCursor._iDeferCounter;
 
     // Size will be handled separately in the resize operation.
     //_ulSize                       = OtherCursor._ulSize;
@@ -312,17 +314,22 @@ bool Cursor::IsDelayedEOLWrap() const noexcept
 
 void Cursor::StartDeferDrawing() noexcept
 {
-    _fDeferCursorRedraw = true;
+    ++_iDeferCounter;
 }
 
 void Cursor::EndDeferDrawing() noexcept
 {
-    if (_fHaveDeferredCursorRedraw)
+    // Nobody has started a defer drawing.
+    if (_iDeferCounter == 0)
     {
-        _RedrawCursorAlways();
+        return;
     }
 
-    _fDeferCursorRedraw = FALSE;
+    --_iDeferCounter;
+    if (_iDeferCounter == 0)
+    {
+        _RedrawCursorAlways();
+    }
 }
 
 const CursorType Cursor::GetType() const noexcept
diff --git a/src/buffer/out/cursor.h b/src/buffer/out/cursor.h
index 7ac93359a49..d47cdd8825d 100644
--- a/src/buffer/out/cursor.h
+++ b/src/buffer/out/cursor.h
@@ -107,6 +107,7 @@ class Cursor final
     bool _fDelayedEolWrap; // don't wrap at EOL till the next char comes in.
     COORD _coordDelayedAt; // coordinate the EOL wrap was delayed at.
 
+    int _iDeferCounter;
     bool _fDeferCursorRedraw; // whether we should defer redrawing the cursor or not
     bool _fHaveDeferredCursorRedraw; // have we been asked to redraw the cursor while it was being deferred?
 
diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 272bc4c5934..ef670f8ce87 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -166,11 +166,6 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 {
     const auto oldDimensions = _mutableViewport.Dimensions();
 
-    if (!_buffer->GetSize().IsInBounds(_buffer->GetCursor().GetPosition()))
-    {
-        OutputDebugString(L"UserResize not in bounds\n");
-    }   
-
     if (viewportSize == oldDimensions)
     {
         return S_FALSE;
@@ -196,6 +191,23 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
     // bottom in the new buffer as well. Track that case now.
     const bool originalOffsetWasZero = _scrollOffset == 0;
 
+    // Defer the cursor drawing here right before the Reflow call
+    // because we only want the renderer to redraw the cursor right
+    // after we swap out the old buffer with the new buffer from Reflow.
+    // This swap happens down below, and so we'll EndDeferDrawing right
+    // after the swap.
+    // What would happen is that at the end of Reflow, we would call
+    // EndDeferDrawing, causing the renderer to go and attempt to redraw
+    // the cursor. However there's a race condition where, sometimes it
+    // would check for the _buffer properties before we swap out the
+    // buffer with the new one. This would make it crash if the old
+    // buffer's cursor position was out of bounds.
+    // Now that StartDeferDrawing uses a counter and will only redraw
+    // when the counter reaches 0, this StartDeferDrawing call here will
+    // force the renderer to redraw at least until this particular
+    // deferral is met with its corresponding EndDeferral down below.
+    _buffer->GetCursor().StartDeferDrawing();
+
     // First allocate a new text buffer to take the place of the current one.
     std::unique_ptr<TextBuffer> newTextBuffer;
     try
@@ -335,6 +347,8 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 
     _buffer.swap(newTextBuffer);
 
+    _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());
@@ -716,11 +730,6 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             // -> Increment "i" by 1 in that case and thus by 2 in total in this iteration.
             proposedCursorPosition.X += gsl::narrow<SHORT>(cellDistance);
 
-            if (!_buffer->GetSize().IsInBounds(proposedCursorPosition))
-            {
-                OutputDebugString(L"InDist > 0 not in Bounds\n");
-            }
-
             i += inputDistance - 1;
         }
         else
@@ -737,8 +746,6 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             // Try the character again.
             i--;
 
-            OutputDebugString(L"Reset to 0\n");
-
             // If we write the last cell of the row here, TextBuffer::Write will
             // mark this line as wrapped for us. If the next character we
             // process is a newline, the Terminal::CursorLineFeed will unmark
@@ -753,11 +760,6 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
         _AdjustCursorPosition(proposedCursorPosition);
     }
 
-    if (!_buffer->GetSize().IsInBounds(_buffer->GetCursor().GetPosition()))
-    {
-        OutputDebugString(L"Still not in Bounds\n");
-    }
-
     cursor.EndDeferDrawing();
 }
 
diff --git a/src/renderer/base/renderer.cpp b/src/renderer/base/renderer.cpp
index ef293999c5c..88847c04bac 100644
--- a/src/renderer/base/renderer.cpp
+++ b/src/renderer/base/renderer.cpp
@@ -236,6 +236,13 @@ void Renderer::TriggerRedrawCursor(const COORD* const pcoord)
         {
             LOG_IF_FAILED(pEngine->InvalidateCursor(&updateCoord));
 
+            if (!_pData->GetTextBuffer().GetSize().IsInBounds(_pData->GetTextBuffer().GetCursor().GetPosition()))
+            {
+                char buf[2000];
+                sprintf_s(buf, "TriggerRedraw: bufferX: %d, cursorpos: %d, updateCoord: %d\n", gsl::narrow_cast<int>(_pData->GetTextBuffer().GetSize().RightExclusive()), gsl::narrow_cast<int>(_pData->GetTextBuffer().GetCursor().GetPosition().X), updateCoord.X);
+                OutputDebugStringA(buf);
+            }
+
             // Double-wide cursors need to invalidate the right half as well.
             if (_pData->IsCursorDoubleWidth())
             {
@@ -832,10 +839,6 @@ void Renderer::_PaintCursor(_In_ IRenderEngine* const pEngine)
             // Draw it within the viewport
             LOG_IF_FAILED(pEngine->PaintCursor(options));
         }
-        else
-        {
-            OutputDebugString(L"PaintCursor NOT In Bounds \n");
-        }
     }
 }
 

From 32af07a3847e5c31e1ff7a1b139a5f1e66610b87 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Wed, 8 Apr 2020 15:38:30 -0700
Subject: [PATCH 06/18] ridding myself of comments

---
 src/cascadia/TerminalCore/Terminal.cpp | 1 -
 src/renderer/base/renderer.cpp         | 7 -------
 2 files changed, 8 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index ef670f8ce87..b319e294ac0 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -729,7 +729,6 @@ void Terminal::_WriteBuffer(const std::wstring_view& stringView)
             // If "wch" was a surrogate character, we just consumed 2 code units above.
             // -> Increment "i" by 1 in that case and thus by 2 in total in this iteration.
             proposedCursorPosition.X += gsl::narrow<SHORT>(cellDistance);
-
             i += inputDistance - 1;
         }
         else
diff --git a/src/renderer/base/renderer.cpp b/src/renderer/base/renderer.cpp
index 88847c04bac..dfe4bdd3a6d 100644
--- a/src/renderer/base/renderer.cpp
+++ b/src/renderer/base/renderer.cpp
@@ -236,13 +236,6 @@ void Renderer::TriggerRedrawCursor(const COORD* const pcoord)
         {
             LOG_IF_FAILED(pEngine->InvalidateCursor(&updateCoord));
 
-            if (!_pData->GetTextBuffer().GetSize().IsInBounds(_pData->GetTextBuffer().GetCursor().GetPosition()))
-            {
-                char buf[2000];
-                sprintf_s(buf, "TriggerRedraw: bufferX: %d, cursorpos: %d, updateCoord: %d\n", gsl::narrow_cast<int>(_pData->GetTextBuffer().GetSize().RightExclusive()), gsl::narrow_cast<int>(_pData->GetTextBuffer().GetCursor().GetPosition().X), updateCoord.X);
-                OutputDebugStringA(buf);
-            }
-
             // Double-wide cursors need to invalidate the right half as well.
             if (_pData->IsCursorDoubleWidth())
             {

From 69b0f27edacb730fb3b9a0e599ab462c3c0bd2b5 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Thu, 9 Apr 2020 12:41:37 -0700
Subject: [PATCH 07/18] y fail if it wouldn't matter hmm

---
 src/cascadia/TerminalCore/Terminal.cpp           |  1 -
 src/cascadia/TerminalCore/terminalrenderdata.cpp | 15 +++++++++++++--
 src/host/ft_host/API_OutputTests.cpp             | 15 ---------------
 3 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index b319e294ac0..6073596dc1e 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -165,7 +165,6 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 [[nodiscard]] HRESULT Terminal::UserResize(const COORD viewportSize) noexcept
 {
     const auto oldDimensions = _mutableViewport.Dimensions();
-
     if (viewportSize == oldDimensions)
     {
         return S_FALSE;
diff --git a/src/cascadia/TerminalCore/terminalrenderdata.cpp b/src/cascadia/TerminalCore/terminalrenderdata.cpp
index 686b2334575..0d23d884a1e 100644
--- a/src/cascadia/TerminalCore/terminalrenderdata.cpp
+++ b/src/cascadia/TerminalCore/terminalrenderdata.cpp
@@ -108,8 +108,19 @@ COLORREF Terminal::GetCursorColor() const noexcept
 bool Terminal::IsCursorDoubleWidth() const noexcept
 {
     const auto position = _buffer->GetCursor().GetPosition();
-    TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
-    return IsGlyphFullWidth(*it);
+
+    if (_buffer->GetSize().IsInBounds(position))
+    {
+        TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
+        return IsGlyphFullWidth(*it);
+    }
+    else
+    {
+        // If the cursor isn't in the bounds of the buffer for any reason,
+        // it won't be rendered anyway, so let's just say the cursor
+        // was single width.
+        return false;
+    }
 }
 
 const std::vector<RenderOverlay> Terminal::GetOverlays() const noexcept
diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index 499eab10b7f..22a9a2eb9ab 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -1102,19 +1102,4 @@ void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
 
     // Move the cursor to the last column of the buffer
     VERIFY_WIN32_BOOL_SUCCEEDED(SetConsoleCursorPosition(consoleOutputHandle, { bufferSize.X - 1, 0 }));
-
-    //// Make an array that can hold the output
-    //std::vector<CHAR_INFO> readBuffer(regionSize);
-
-    //// Call the API and confirm results
-    //SMALL_RECT readRegion = region;
-    //VERIFY_WIN32_BOOL_SUCCEEDED(ReadConsoleOutputW(consoleOutputHandle, readBuffer.data(), regionDimensions, regionOrigin, &readRegion));
-    //for (auto x : readBuffer)
-    //{
-    //    for (int i = 0; i < 1000; ++i)
-    //    {
-    //        VERIFY_ARE_EQUAL(x, testValue);
-    //    }
-    //    
-    //}
 }

From 21fd1b3476e26763f66163282ec929473dc08693 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Thu, 9 Apr 2020 16:50:08 -0700
Subject: [PATCH 08/18] why don't we just take these calls and place them over
 here

---
 src/buffer/out/cursor.cpp                     | 19 ++++---------
 src/buffer/out/cursor.h                       |  1 -
 src/buffer/out/textBuffer.cpp                 |  6 ----
 src/cascadia/TerminalCore/Terminal.cpp        | 28 +++++++------------
 .../TerminalCore/terminalrenderdata.cpp       | 15 ++--------
 src/host/ft_host/API_OutputTests.cpp          |  2 +-
 src/host/screenInfo.cpp                       |  8 ++++++
 7 files changed, 27 insertions(+), 52 deletions(-)

diff --git a/src/buffer/out/cursor.cpp b/src/buffer/out/cursor.cpp
index 359a3eb43d1..46f0208f820 100644
--- a/src/buffer/out/cursor.cpp
+++ b/src/buffer/out/cursor.cpp
@@ -29,8 +29,7 @@ Cursor::Cursor(const ULONG ulSize, TextBuffer& parentBuffer) noexcept :
     _ulSize(ulSize),
     _cursorType(CursorType::Legacy),
     _fUseColor(false),
-    _color(s_InvertCursorColor),
-    _iDeferCounter{ 0 }
+    _color(s_InvertCursorColor)
 {
 }
 
@@ -167,7 +166,7 @@ void Cursor::_RedrawCursor() noexcept
     // (Conversion areas have cursors to mark the insertion point internally, but the user's actual cursor is the one on the primary screen buffer.)
     if (IsOn() && !IsConversionArea())
     {
-        if (_iDeferCounter > 0)
+        if (_fDeferCursorRedraw)
         {
             _fHaveDeferredCursorRedraw = true;
         }
@@ -282,7 +281,6 @@ void Cursor::CopyProperties(const Cursor& OtherCursor) noexcept
 
     _fDeferCursorRedraw = OtherCursor._fDeferCursorRedraw;
     _fHaveDeferredCursorRedraw = OtherCursor._fHaveDeferredCursorRedraw;
-    _iDeferCounter = OtherCursor._iDeferCounter;
 
     // Size will be handled separately in the resize operation.
     //_ulSize                       = OtherCursor._ulSize;
@@ -314,22 +312,17 @@ bool Cursor::IsDelayedEOLWrap() const noexcept
 
 void Cursor::StartDeferDrawing() noexcept
 {
-    ++_iDeferCounter;
+    _fDeferCursorRedraw = true;
 }
 
 void Cursor::EndDeferDrawing() noexcept
 {
-    // Nobody has started a defer drawing.
-    if (_iDeferCounter == 0)
-    {
-        return;
-    }
-
-    --_iDeferCounter;
-    if (_iDeferCounter == 0)
+    if (_fHaveDeferredCursorRedraw)
     {
         _RedrawCursorAlways();
     }
+
+    _fDeferCursorRedraw = FALSE;
 }
 
 const CursorType Cursor::GetType() const noexcept
diff --git a/src/buffer/out/cursor.h b/src/buffer/out/cursor.h
index d47cdd8825d..7ac93359a49 100644
--- a/src/buffer/out/cursor.h
+++ b/src/buffer/out/cursor.h
@@ -107,7 +107,6 @@ class Cursor final
     bool _fDelayedEolWrap; // don't wrap at EOL till the next char comes in.
     COORD _coordDelayedAt; // coordinate the EOL wrap was delayed at.
 
-    int _iDeferCounter;
     bool _fDeferCursorRedraw; // whether we should defer redrawing the cursor or not
     bool _fHaveDeferredCursorRedraw; // have we been asked to redraw the cursor while it was being deferred?
 
diff --git a/src/buffer/out/textBuffer.cpp b/src/buffer/out/textBuffer.cpp
index eaa41dc415a..eb92fe9055e 100644
--- a/src/buffer/out/textBuffer.cpp
+++ b/src/buffer/out/textBuffer.cpp
@@ -1969,9 +1969,6 @@ HRESULT TextBuffer::Reflow(TextBuffer& oldBuffer,
 {
     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;
 }
diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 6073596dc1e..211aaccfd22 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -190,23 +190,6 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
     // bottom in the new buffer as well. Track that case now.
     const bool originalOffsetWasZero = _scrollOffset == 0;
 
-    // Defer the cursor drawing here right before the Reflow call
-    // because we only want the renderer to redraw the cursor right
-    // after we swap out the old buffer with the new buffer from Reflow.
-    // This swap happens down below, and so we'll EndDeferDrawing right
-    // after the swap.
-    // What would happen is that at the end of Reflow, we would call
-    // EndDeferDrawing, causing the renderer to go and attempt to redraw
-    // the cursor. However there's a race condition where, sometimes it
-    // would check for the _buffer properties before we swap out the
-    // buffer with the new one. This would make it crash if the old
-    // buffer's cursor position was out of bounds.
-    // Now that StartDeferDrawing uses a counter and will only redraw
-    // when the counter reaches 0, this StartDeferDrawing call here will
-    // force the renderer to redraw at least until this particular
-    // deferral is met with its corresponding EndDeferral down below.
-    _buffer->GetCursor().StartDeferDrawing();
-
     // First allocate a new text buffer to take the place of the current one.
     std::unique_ptr<TextBuffer> newTextBuffer;
     try
@@ -216,6 +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.
@@ -239,7 +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
@@ -346,6 +337,7 @@ 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
diff --git a/src/cascadia/TerminalCore/terminalrenderdata.cpp b/src/cascadia/TerminalCore/terminalrenderdata.cpp
index 0d23d884a1e..686b2334575 100644
--- a/src/cascadia/TerminalCore/terminalrenderdata.cpp
+++ b/src/cascadia/TerminalCore/terminalrenderdata.cpp
@@ -108,19 +108,8 @@ COLORREF Terminal::GetCursorColor() const noexcept
 bool Terminal::IsCursorDoubleWidth() const noexcept
 {
     const auto position = _buffer->GetCursor().GetPosition();
-
-    if (_buffer->GetSize().IsInBounds(position))
-    {
-        TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
-        return IsGlyphFullWidth(*it);
-    }
-    else
-    {
-        // If the cursor isn't in the bounds of the buffer for any reason,
-        // it won't be rendered anyway, so let's just say the cursor
-        // was single width.
-        return false;
-    }
+    TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
+    return IsGlyphFullWidth(*it);
 }
 
 const std::vector<RenderOverlay> Terminal::GetOverlays() const noexcept
diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index 22a9a2eb9ab..04369896259 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -1077,7 +1077,7 @@ void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
     VERIFY_WIN32_BOOL_SUCCEEDED(GetConsoleScreenBufferInfoEx(consoleOutputHandle, &sbiex));
     const auto bufferSize = sbiex.dwSize;
 
-    // Establish a writing region that is the width of the buffer and half the height.
+    // Establish a writing region that is the width of the buffer and just one row tall.
     const SMALL_RECT region{ 0, 0, bufferSize.X - 1, 0 };
     const COORD regionDimensions{ region.Right - region.Left + 1, region.Bottom - region.Top + 1 };
     const auto regionSize = regionDimensions.X * regionDimensions.Y;
diff --git a/src/host/screenInfo.cpp b/src/host/screenInfo.cpp
index b893c1962cd..cfbb2dcf845 100644
--- a/src/host/screenInfo.cpp
+++ b/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);
 }
 

From 91e4fb80838c16fc4530ebff06e5075f0551444f Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Fri, 10 Apr 2020 14:06:47 -0700
Subject: [PATCH 09/18] added test case to idk if this is right place

---
 .../TerminalApiTest.cpp                       | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/src/cascadia/UnitTests_TerminalCore/TerminalApiTest.cpp b/src/cascadia/UnitTests_TerminalCore/TerminalApiTest.cpp
index 3e715e44fd5..b236765bb43 100644
--- a/src/cascadia/UnitTests_TerminalCore/TerminalApiTest.cpp
+++ b/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());
+}

From 51f6cce895362f37269dcaaba19819cba285f6c2 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Fri, 10 Apr 2020 14:07:53 -0700
Subject: [PATCH 10/18] remove this

---
 src/host/ft_host/API_OutputTests.cpp | 41 ----------------------------
 1 file changed, 41 deletions(-)

diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index 04369896259..0f3e88ebd47 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -46,8 +46,6 @@ class OutputTests
     TEST_METHOD(WriteBackspaceTest);
 
     TEST_METHOD(WinPtyWrite);
-
-    TEST_METHOD(WriteTwoColumnCharacterToCheckOverflow);
 };
 
 bool OutputTests::TestSetup()
@@ -1064,42 +1062,3 @@ void OutputTests::WinPtyWrite()
         break;
     }
 }
-
-void OutputTests::WriteTwoColumnCharacterToCheckOverflow()
-{
-    // Get output buffer information.
-    const auto consoleOutputHandle = GetStdOutputHandle();
-    SetConsoleActiveScreenBuffer(consoleOutputHandle);
-
-    CONSOLE_SCREEN_BUFFER_INFOEX sbiex{ 0 };
-    sbiex.cbSize = sizeof(sbiex);
-
-    VERIFY_WIN32_BOOL_SUCCEEDED(GetConsoleScreenBufferInfoEx(consoleOutputHandle, &sbiex));
-    const auto bufferSize = sbiex.dwSize;
-
-    // Establish a writing region that is the width of the buffer and just one row tall.
-    const SMALL_RECT region{ 0, 0, bufferSize.X - 1, 0 };
-    const COORD regionDimensions{ region.Right - region.Left + 1, region.Bottom - region.Top + 1 };
-    const auto regionSize = regionDimensions.X * regionDimensions.Y;
-    const COORD regionOrigin{ 0, 0 };
-
-    CHAR_INFO testValue;
-    testValue.Attributes = 0x3e;
-    testValue.Char.UnicodeChar = L'A';
-
-    std::vector<CHAR_INFO> buffer(regionSize, testValue);
-
-    // Place a double width character with a lead bit in the last column of the buffer.
-    CHAR_INFO lastColumnValue;
-    lastColumnValue.Attributes = 0x13e;
-    lastColumnValue.Char.UnicodeChar = L'我';
-    buffer[regionSize - 1] = lastColumnValue;
-
-    // Call the API and confirm results.
-    SMALL_RECT affected = region;
-    VERIFY_WIN32_BOOL_SUCCEEDED(WriteConsoleOutputW(consoleOutputHandle, buffer.data(), regionDimensions, regionOrigin, &affected));
-    VERIFY_ARE_EQUAL(region, affected);
-
-    // Move the cursor to the last column of the buffer
-    VERIFY_WIN32_BOOL_SUCCEEDED(SetConsoleCursorPosition(consoleOutputHandle, { bufferSize.X - 1, 0 }));
-}

From 640bc695dff4558393ef0433f841a7e34bb2e26f Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Fri, 10 Apr 2020 14:13:47 -0700
Subject: [PATCH 11/18] reverting this file

---
 src/host/ft_host/API_OutputTests.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/host/ft_host/API_OutputTests.cpp b/src/host/ft_host/API_OutputTests.cpp
index 0f3e88ebd47..4912f17a597 100644
--- a/src/host/ft_host/API_OutputTests.cpp
+++ b/src/host/ft_host/API_OutputTests.cpp
@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
 #include "precomp.h"

From ae430ce9ca6416f919961ecea6220c86d68c621a Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Fri, 10 Apr 2020 15:16:50 -0700
Subject: [PATCH 12/18] wtf

---
 src/buffer/out/textBuffer.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/buffer/out/textBuffer.cpp b/src/buffer/out/textBuffer.cpp
index eb92fe9055e..1fbf1bbea1d 100644
--- a/src/buffer/out/textBuffer.cpp
+++ b/src/buffer/out/textBuffer.cpp
@@ -1967,7 +1967,7 @@ 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();
 
     // We need to save the old cursor position so that we can

From 3509c9f9adbe2f5be541574a6d49dcafb4094ad1 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Mon, 13 Apr 2020 14:43:20 -0700
Subject: [PATCH 13/18] build is complaining, more returns

---
 src/cascadia/TerminalCore/Terminal.cpp        | 19 +++++++++++++------
 src/cascadia/TerminalCore/Terminal.hpp        |  2 +-
 .../TerminalCore/terminalrenderdata.cpp       |  2 +-
 src/renderer/inc/IRenderData.hpp              |  2 +-
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 211aaccfd22..58de489b88b 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -190,6 +190,9 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
     // bottom in the new buffer as well. Track that case now.
     const bool originalOffsetWasZero = _scrollOffset == 0;
 
+    // skip any drawing updates that might occur until we swap _buffer with the new buffer.
+    _buffer->GetCursor().StartDeferDrawing();
+
     // First allocate a new text buffer to take the place of the current one.
     std::unique_ptr<TextBuffer> newTextBuffer;
     try
@@ -199,8 +202,6 @@ 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
@@ -218,10 +219,16 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
         oldRows.visibleViewportTop = newVisibleTop;
 
         const std::optional<short> oldViewStart{ oldViewportTop };
-        RETURN_IF_FAILED(TextBuffer::Reflow(*_buffer.get(),
-                                            *newTextBuffer.get(),
-                                            _mutableViewport,
-                                            { oldRows }));
+        const HRESULT reflowHR = TextBuffer::Reflow(*_buffer.get(),
+                                                    *newTextBuffer.get(),
+                                                    _mutableViewport,
+                                                    { oldRows });
+
+        if (FAILED(reflowHR))
+        {
+            _buffer->GetCursor().EndDeferDrawing();
+            return reflowHR;
+        }
 
         newViewportTop = oldRows.mutableViewportTop;
         newVisibleTop = oldRows.visibleViewportTop;
diff --git a/src/cascadia/TerminalCore/Terminal.hpp b/src/cascadia/TerminalCore/Terminal.hpp
index 59d0bad4d96..9c8334edbb5 100644
--- a/src/cascadia/TerminalCore/Terminal.hpp
+++ b/src/cascadia/TerminalCore/Terminal.hpp
@@ -148,7 +148,7 @@ class Microsoft::Terminal::Core::Terminal final :
     ULONG GetCursorPixelWidth() const noexcept override;
     CursorType GetCursorStyle() const noexcept override;
     COLORREF GetCursorColor() const noexcept override;
-    bool IsCursorDoubleWidth() const noexcept override;
+    bool IsCursorDoubleWidth() const override;
     bool IsScreenReversed() const noexcept override;
     const std::vector<Microsoft::Console::Render::RenderOverlay> GetOverlays() const noexcept override;
     const bool IsGridLineDrawingAllowed() noexcept override;
diff --git a/src/cascadia/TerminalCore/terminalrenderdata.cpp b/src/cascadia/TerminalCore/terminalrenderdata.cpp
index 686b2334575..01672a047d1 100644
--- a/src/cascadia/TerminalCore/terminalrenderdata.cpp
+++ b/src/cascadia/TerminalCore/terminalrenderdata.cpp
@@ -105,7 +105,7 @@ COLORREF Terminal::GetCursorColor() const noexcept
     return _buffer->GetCursor().GetColor();
 }
 
-bool Terminal::IsCursorDoubleWidth() const noexcept
+bool Terminal::IsCursorDoubleWidth() const
 {
     const auto position = _buffer->GetCursor().GetPosition();
     TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
diff --git a/src/renderer/inc/IRenderData.hpp b/src/renderer/inc/IRenderData.hpp
index 860537514ff..c504ae2dbb3 100644
--- a/src/renderer/inc/IRenderData.hpp
+++ b/src/renderer/inc/IRenderData.hpp
@@ -58,7 +58,7 @@ namespace Microsoft::Console::Render
         virtual CursorType GetCursorStyle() const noexcept = 0;
         virtual ULONG GetCursorPixelWidth() const noexcept = 0;
         virtual COLORREF GetCursorColor() const noexcept = 0;
-        virtual bool IsCursorDoubleWidth() const noexcept = 0;
+        virtual bool IsCursorDoubleWidth() const = 0;
 
         virtual bool IsScreenReversed() const noexcept = 0;
 

From 8e70d831c7867691d1dd0775b7787e312060a4e6 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Mon, 13 Apr 2020 15:11:15 -0700
Subject: [PATCH 14/18] what about nOW

---
 src/cascadia/TerminalCore/Terminal.cpp | 2 +-
 src/cascadia/TerminalCore/Terminal.hpp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 58de489b88b..ea4ab3d1a6e 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -893,7 +893,7 @@ CATCH_LOG()
 //   Visible, then it will immediately become visible.
 // Arguments:
 // - isVisible: whether the cursor should be visible
-void Terminal::SetCursorOn(const bool isOn) noexcept
+void Terminal::SetCursorOn(const bool isOn)
 {
     auto lock = LockForWriting();
     _buffer->GetCursor().SetIsOn(isOn);
diff --git a/src/cascadia/TerminalCore/Terminal.hpp b/src/cascadia/TerminalCore/Terminal.hpp
index 9c8334edbb5..313f0f6b34e 100644
--- a/src/cascadia/TerminalCore/Terminal.hpp
+++ b/src/cascadia/TerminalCore/Terminal.hpp
@@ -172,7 +172,7 @@ class Microsoft::Terminal::Core::Terminal final :
     void SetCursorPositionChangedCallback(std::function<void()> pfn) noexcept;
     void SetBackgroundCallback(std::function<void(const uint32_t)> pfn) noexcept;
 
-    void SetCursorOn(const bool isOn) noexcept;
+    void SetCursorOn(const bool isOn);
     bool IsCursorBlinkingAllowed() const noexcept;
 
 #pragma region TextSelection

From 1a3a312a1ed4c656d8686f75977ff783cc414b84 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 14 Apr 2020 14:30:46 -0700
Subject: [PATCH 15/18] this is a much better thing

---
 src/cascadia/TerminalCore/Terminal.cpp | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 58de489b88b..f87830aae11 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -190,8 +190,9 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
     // bottom in the new buffer as well. Track that case now.
     const bool originalOffsetWasZero = _scrollOffset == 0;
 
-    // skip any drawing updates that might occur until we swap _buffer with the new buffer.
+    // skip any drawing updates that might occur until we swap _buffer with the new buffer or if we exit early.
     _buffer->GetCursor().StartDeferDrawing();
+    auto endDefer = wil::scope_exit([&] { _buffer->GetCursor().EndDeferDrawing(); });
 
     // First allocate a new text buffer to take the place of the current one.
     std::unique_ptr<TextBuffer> newTextBuffer;
@@ -224,20 +225,10 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
                                                     _mutableViewport,
                                                     { oldRows });
 
-        if (FAILED(reflowHR))
-        {
-            _buffer->GetCursor().EndDeferDrawing();
-            return reflowHR;
-        }
-
         newViewportTop = oldRows.mutableViewportTop;
         newVisibleTop = oldRows.visibleViewportTop;
     }
-    catch (...)
-    {
-        _buffer->GetCursor().EndDeferDrawing();
-        RETURN_CAUGHT_EXCEPTION();
-    }
+    CATCH_RETURN();
 
     // 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
@@ -344,9 +335,6 @@ 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());

From 3e4252bf4a919aee2b5a223b450340f5efaf8c11 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 14 Apr 2020 14:37:13 -0700
Subject: [PATCH 16/18] conhost can also use this, and i forgot to put
 something back in

---
 src/cascadia/TerminalCore/Terminal.cpp | 8 ++++----
 src/host/screenInfo.cpp                | 6 +-----
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 0c04b75cfba..201e34a27de 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -220,10 +220,10 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
         oldRows.visibleViewportTop = newVisibleTop;
 
         const std::optional<short> oldViewStart{ oldViewportTop };
-        const HRESULT reflowHR = TextBuffer::Reflow(*_buffer.get(),
-                                                    *newTextBuffer.get(),
-                                                    _mutableViewport,
-                                                    { oldRows });
+        RETURN_IF_FAILED(TextBuffer::Reflow(*_buffer.get(),
+                                            *newTextBuffer.get(),
+                                            _mutableViewport,
+                                            { oldRows }));
 
         newViewportTop = oldRows.mutableViewportTop;
         newVisibleTop = oldRows.visibleViewportTop;
diff --git a/src/host/screenInfo.cpp b/src/host/screenInfo.cpp
index cfbb2dcf845..2880d77be71 100644
--- a/src/host/screenInfo.cpp
+++ b/src/host/screenInfo.cpp
@@ -1403,9 +1403,9 @@ 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();
+    auto endDefer = wil::scope_exit([&] { _textBuffer->GetCursor().EndDeferDrawing(); });
 
     HRESULT hr = TextBuffer::Reflow(*_textBuffer.get(), *newTextBuffer.get(), std::nullopt, std::nullopt);
 
@@ -1421,10 +1421,6 @@ 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);
 }
 

From cf32371cb915192d53d167da94100b3162ee8fe2 Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 14 Apr 2020 14:53:11 -0700
Subject: [PATCH 17/18] i am getting absolutely destroyed by mr static

---
 src/cascadia/TerminalCore/Terminal.cpp | 2 +-
 src/host/screenInfo.cpp                | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 201e34a27de..4991ab0c2a2 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -192,7 +192,7 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 
     // skip any drawing updates that might occur until we swap _buffer with the new buffer or if we exit early.
     _buffer->GetCursor().StartDeferDrawing();
-    auto endDefer = wil::scope_exit([&] { _buffer->GetCursor().EndDeferDrawing(); });
+    auto endDefer = wil::scope_exit([&]() noexcept { _buffer->GetCursor().EndDeferDrawing(); });
 
     // First allocate a new text buffer to take the place of the current one.
     std::unique_ptr<TextBuffer> newTextBuffer;
diff --git a/src/host/screenInfo.cpp b/src/host/screenInfo.cpp
index 2880d77be71..4edd0e500b0 100644
--- a/src/host/screenInfo.cpp
+++ b/src/host/screenInfo.cpp
@@ -1405,7 +1405,7 @@ bool SCREEN_INFORMATION::IsMaximizedY() const
 
     newTextBuffer->GetCursor().StartDeferDrawing();
     _textBuffer->GetCursor().StartDeferDrawing();
-    auto endDefer = wil::scope_exit([&] { _textBuffer->GetCursor().EndDeferDrawing(); });
+    auto endDefer = wil::scope_exit([&]() noexcept { _textBuffer->GetCursor().EndDeferDrawing(); });
 
     HRESULT hr = TextBuffer::Reflow(*_textBuffer.get(), *newTextBuffer.get(), std::nullopt, std::nullopt);
 

From 2216cb9a1052157298c5b2ae87dfa06a67dfdded Mon Sep 17 00:00:00 2001
From: Leon Liang <lelian@microsoft.com>
Date: Tue, 14 Apr 2020 15:02:43 -0700
Subject: [PATCH 18/18] comment

---
 src/cascadia/TerminalCore/Terminal.cpp | 1 +
 src/host/screenInfo.cpp                | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/src/cascadia/TerminalCore/Terminal.cpp b/src/cascadia/TerminalCore/Terminal.cpp
index 4991ab0c2a2..56c9c8f7c26 100644
--- a/src/cascadia/TerminalCore/Terminal.cpp
+++ b/src/cascadia/TerminalCore/Terminal.cpp
@@ -192,6 +192,7 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
 
     // skip any drawing updates that might occur until we swap _buffer with the new buffer or if we exit early.
     _buffer->GetCursor().StartDeferDrawing();
+    // we're capturing _buffer by reference here because when we exit, we want to EndDefer on the current active buffer.
     auto endDefer = wil::scope_exit([&]() noexcept { _buffer->GetCursor().EndDeferDrawing(); });
 
     // First allocate a new text buffer to take the place of the current one.
diff --git a/src/host/screenInfo.cpp b/src/host/screenInfo.cpp
index 4edd0e500b0..eaa5185e017 100644
--- a/src/host/screenInfo.cpp
+++ b/src/host/screenInfo.cpp
@@ -1403,8 +1403,10 @@ bool SCREEN_INFORMATION::IsMaximizedY() const
     // Save cursor's relative height versus the viewport
     SHORT const sCursorHeightInViewportBefore = _textBuffer->GetCursor().GetPosition().Y - _viewport.Top();
 
+    // skip any drawing updates that might occur until we swap _textBuffer with the new buffer or we exit early.
     newTextBuffer->GetCursor().StartDeferDrawing();
     _textBuffer->GetCursor().StartDeferDrawing();
+    // we're capturing _textBuffer by reference here because when we exit, we want to EndDefer on the current active buffer.
     auto endDefer = wil::scope_exit([&]() noexcept { _textBuffer->GetCursor().EndDeferDrawing(); });
 
     HRESULT hr = TextBuffer::Reflow(*_textBuffer.get(), *newTextBuffer.get(), std::nullopt, std::nullopt);