Optimize hot path in textBufferCellIterator

src/buffer/out/OutputCellView.hpp

@@ -6,7 +6,7 @@ Module Name:
 - OutputCellView.hpp
 
 Abstract:
-- Read-only view into a single cell of data that someone is attempting to write into the output buffer.
+- Read view into a single cell of data that someone is attempting to write into the output buffer.
 - This is done for performance reasons (avoid heap allocs and copies).
 
 Author:
@@ -36,6 +36,21 @@ class OutputCellView
     TextAttribute TextAttr() const noexcept;
     TextAttributeBehavior TextAttrBehavior() const noexcept;
 
+    void UpdateText(const std::wstring_view& view) noexcept
+    {
+        _view = view;
+    };
+
+    void UpdateDbcsAttribute(const DbcsAttribute& dbcsAttr) noexcept
+    {
+        _dbcsAttr = dbcsAttr;
+    }
+
+    void UpdateTextAttribute(const TextAttribute& textAttr) noexcept
+    {
+        _textAttr = textAttr;
+    }
+
     bool operator==(const OutputCellView& view) const noexcept;
     bool operator!=(const OutputCellView& view) const noexcept;
 

src/buffer/out/textBufferCellIterator.cpp

@@ -95,18 +95,66 @@ bool TextBufferCellIterator::operator!=(const TextBufferCellIterator& it) const
 TextBufferCellIterator& TextBufferCellIterator::operator+=(const ptrdiff_t& movement)
 {
     ptrdiff_t move = movement;
-    auto newPos = _pos;
-    while (move > 0 && !_exceeded)
+    if (move < 0)
+    {
+        return (*this) -= (-move);
+    }
+
+    auto oldX = _pos.X;
+    auto newX = oldX;
+    auto newY = _pos.Y;
+    bool yChanged = false;
+    const auto boundsRightInclusive = _bounds.RightInclusive();
+    const auto boundsLeft = _bounds.Left();
+    const auto boundsBottomInclusive = _bounds.BottomInclusive();
+    const auto boundsTop = _bounds.Top();
+    while (move > 0)
     {
-        _exceeded = !_bounds.IncrementInBounds(newPos);
+        if (newX == boundsRightInclusive)
+        {
+            newX = boundsLeft;
+            newY++;
+            yChanged = true;
+            if (newY > boundsBottomInclusive)
+            {
+                newY = boundsTop;
+                _exceeded = true;
+                break;
+            }
+        }
+        else
+        {
+            newX++;
+            _exceeded = false;
+        }
         move--;
     }
-    while (move < 0 && !_exceeded)
+
+    if (_exceeded)
     {
-        _exceeded = !_bounds.DecrementInBounds(newPos);
-        move++;
+        return (*this);
+    }
+
+    if (yChanged)
+    {
+        _pRow = s_GetRow(_buffer, { newX, newY });
+        _attrIter = _pRow->GetAttrRow().cbegin() + newX;
+        _pos.X = newX;
+        _pos.Y = newY;
+        _GenerateView();
+    }
+    else
+    {
+        const auto diff = gsl::narrow_cast<ptrdiff_t>(newX) - gsl::narrow_cast<ptrdiff_t>(oldX);
+        _attrIter += diff;
+        _view.UpdateTextAttribute(*_attrIter);
+
+        const CharRow& charRow = _pRow->GetCharRow();
+        _view.UpdateText(charRow.GlyphAt(newX));
+        _view.UpdateDbcsAttribute(charRow.DbcsAttrAt(newX));
+        _pos.X = newX;
     }
-    _SetPos(newPos);
+
     return (*this);
 }
 
@@ -118,7 +166,36 @@ TextBufferCellIterator& TextBufferCellIterator::operator+=(const ptrdiff_t& move
 // - Reference to self after movement.
 TextBufferCellIterator& TextBufferCellIterator::operator-=(const ptrdiff_t& movement)
 {
-    return this->operator+=(-movement);
+    ptrdiff_t move = movement;
+    if (move < 0)
+    {
+        return (*this) += (-move);
+    }
+
+    auto newPos = _pos;
+    while (move > 0 && !_exceeded)
+    {
+        _exceeded = !_bounds.DecrementInBounds(newPos);
+        move--;
+    }
+
+    if (newPos.Y != _pos.Y)
+    {
+        _pRow = s_GetRow(_buffer, newPos);
+        _attrIter = _pRow->GetAttrRow().cbegin();
+        _pos.X = 0;
+    }
+
+    if (newPos.X != _pos.X)
+    {
+        const auto diff = gsl::narrow_cast<ptrdiff_t>(newPos.X) - gsl::narrow_cast<ptrdiff_t>(_pos.X);
+        _attrIter += diff;
+    }
+
+    _pos = newPos;
+
+    _GenerateView();
+    return (*this);
 }
 
 // Routine Description:
@@ -197,30 +274,6 @@ ptrdiff_t TextBufferCellIterator::operator-(const TextBufferCellIterator& it)
     return _bounds.CompareInBounds(_pos, it._pos);
 }
 
-// Routine Description:
-// - Sets the coordinate position that this iterator will inspect within the text buffer on dereference.
-// Arguments:
-// - newPos - The new coordinate position.
-void TextBufferCellIterator::_SetPos(const COORD newPos)
-{
-    if (newPos.Y != _pos.Y)
-    {
-        _pRow = s_GetRow(_buffer, newPos);
-        _attrIter = _pRow->GetAttrRow().cbegin();
-        _pos.X = 0;
-    }
-
-    if (newPos.X != _pos.X)
-    {
-        const auto diff = gsl::narrow_cast<ptrdiff_t>(newPos.X) - gsl::narrow_cast<ptrdiff_t>(_pos.X);
-        _attrIter += diff;
-    }
-
-    _pos = newPos;
-
-    _GenerateView();
-}
-
 // Routine Description:
 // - Shortcut for pulling the row out of the text buffer embedded in the screen information.
 //   We'll hold and cache this to improve performance over looking it up every time.

src/buffer/out/textBufferCellIterator.hpp

@@ -50,7 +50,6 @@ class TextBufferCellIterator
     COORD Pos() const noexcept;
 
 protected:
-    void _SetPos(const COORD newPos);
     void _GenerateView();
     static const ROW* s_GetRow(const TextBuffer& buffer, const COORD pos);