Enable using the alt buffer in the Terminal

src/buffer/out/textBuffer.cpp

@@ -556,7 +556,7 @@ bool TextBuffer::IncrementCircularBuffer(const bool inVtMode)
 {
     // FirstRow is at any given point in time the array index in the circular buffer that corresponds
     // to the logical position 0 in the window (cursor coordinates and all other coordinates).
-    _renderTarget.TriggerCircling();
+    _renderTarget.TriggerFlush(true);
 
     // Prune hyperlinks to delete obsolete references
     _PruneHyperlinks();

src/cascadia/TerminalCore/ITerminalApi.hpp

@@ -67,6 +67,9 @@ namespace Microsoft::Terminal::Core
         virtual void PushGraphicsRendition(const ::Microsoft::Console::VirtualTerminal::VTParameters options) = 0;
         virtual void PopGraphicsRendition() = 0;
 
+        virtual void UseAlternateScreenBuffer() = 0;
+        virtual void UseMainScreenBuffer() = 0;
+
     protected:
         ITerminalApi() = default;
     };

src/cascadia/TerminalCore/Terminal.hpp

@@ -136,6 +136,8 @@ class Microsoft::Terminal::Core::Terminal final :
     void PushGraphicsRendition(const ::Microsoft::Console::VirtualTerminal::VTParameters options) override;
     void PopGraphicsRendition() override;
 
+    void UseAlternateScreenBuffer() override;
+    void UseMainScreenBuffer() override;
 #pragma endregion
 
 #pragma region ITerminalInput
@@ -319,7 +321,8 @@ class Microsoft::Terminal::Core::Terminal final :
 
     // TODO: These members are not shared by an alt-buffer. They should be
     //      encapsulated, such that a Terminal can have both a main and alt buffer.
-    std::unique_ptr<TextBuffer> _buffer;
+    std::unique_ptr<TextBuffer> _mainBuffer;
+    std::unique_ptr<TextBuffer> _altBuffer;
     Microsoft::Console::Types::Viewport _mutableViewport;
     SHORT _scrollbackLines;
 
@@ -373,6 +376,9 @@ class Microsoft::Terminal::Core::Terminal final :
 
     void _NotifyTerminalCursorPositionChanged() noexcept;
 
+    bool _inAltBuffer() const noexcept;
+    TextBuffer& _activeBuffer() const noexcept;
+
 #pragma region TextSelection
     // These methods are defined in TerminalSelection.cpp
     std::vector<SMALL_RECT> _GetSelectionRects() const noexcept;

src/cascadia/TerminalCore/TerminalDispatch.cpp

@@ -594,6 +594,9 @@ bool TerminalDispatch::_ModeParamsHelper(const DispatchTypes::ModeParams param,
     case DispatchTypes::ModeParams::W32IM_Win32InputMode:
         success = EnableWin32InputMode(enable);
         break;
+    case DispatchTypes::ModeParams::ASB_AlternateScreenBuffer:
+        success = enable ? UseAlternateScreenBuffer() : UseMainScreenBuffer();
+        break;
     default:
         // If no functions to call, overall dispatch was a failure.
         success = false;
@@ -722,3 +725,35 @@ bool TerminalDispatch::HardReset()
 
     return true;
 }
+
+// - ASBSET - Creates and swaps to the alternate screen buffer. In virtual terminals, there exists both a "main"
+//     screen buffer and an alternate. ASBSET creates a new alternate, and switches to it. If there is an already
+//     existing alternate, it is discarded.
+// Arguments:
+// - None
+// Return Value:
+// - True.
+bool TerminalDispatch::UseAlternateScreenBuffer()
+{
+    // TODO GH#3849: When de-duplicating this, the AdaptDispatch version of this calls:
+    // CursorSaveState();
+    _terminalApi.UseAlternateScreenBuffer();
+    _usingAltBuffer = true;
+    return true;
+}
+
+// Routine Description:
+// - ASBRST - From the alternate buffer, returns to the main screen buffer.
+//     From the main screen buffer, does nothing. The alternate is discarded.
+// Arguments:
+// - None
+// Return Value:
+// - True.
+bool TerminalDispatch::UseMainScreenBuffer()
+{
+    _terminalApi.UseMainScreenBuffer();
+    _usingAltBuffer = false;
+    // TODO GH#3849: When de-duplicating this, the AdaptDispatch version of this calls:
+    // CursorRestoreState();
+    return true;
+}

src/cascadia/TerminalCore/TerminalDispatch.hpp

@@ -39,6 +39,9 @@ class TerminalDispatch : public Microsoft::Console::VirtualTerminal::TermDispatc
     bool CarriageReturn() override;
     bool SetWindowTitle(std::wstring_view title) override;
 
+    bool UseAlternateScreenBuffer() override; // ASBSET
+    bool UseMainScreenBuffer() override; // ASBRST
+
     bool HorizontalTabSet() override; // HTS
     bool ForwardTab(const size_t numTabs) override; // CHT, HT
     bool BackwardsTab(const size_t numTabs) override; // CBT
@@ -85,6 +88,7 @@ class TerminalDispatch : public Microsoft::Console::VirtualTerminal::TermDispatc
 
     std::vector<bool> _tabStopColumns;
     bool _initDefaultTabStops = true;
+    bool _usingAltBuffer = false;
 
     size_t _SetRgbColorsHelper(const ::Microsoft::Console::VirtualTerminal::VTParameters options,
                                TextAttribute& attr,

src/cascadia/TerminalCore/TerminalSelection.cpp

@@ -54,7 +54,7 @@ std::vector<SMALL_RECT> Terminal::_GetSelectionRects() const noexcept
 
     try
     {
-        return _buffer->GetTextRects(_selection->start, _selection->end, _blockSelection, false);
+        return _activeBuffer().GetTextRects(_selection->start, _selection->end, _blockSelection, false);
     }
     CATCH_LOG();
     return result;
@@ -182,7 +182,7 @@ void Terminal::SetSelectionEnd(const COORD viewportPos, std::optional<SelectionE
 // - the new start/end for a selection
 std::pair<COORD, COORD> Terminal::_PivotSelection(const COORD targetPos, bool& targetStart) const
 {
-    if (targetStart = _buffer->GetSize().CompareInBounds(targetPos, _selection->pivot) <= 0)
+    if (targetStart = _activeBuffer().GetSize().CompareInBounds(targetPos, _selection->pivot) <= 0)
     {
         // target is before pivot
         // treat target as start
@@ -207,16 +207,16 @@ std::pair<COORD, COORD> Terminal::_ExpandSelectionAnchors(std::pair<COORD, COORD
     COORD start = anchors.first;
     COORD end = anchors.second;
 
-    const auto bufferSize = _buffer->GetSize();
+    const auto bufferSize = _activeBuffer().GetSize();
     switch (_multiClickSelectionMode)
     {
     case SelectionExpansion::Line:
         start = { bufferSize.Left(), start.Y };
         end = { bufferSize.RightInclusive(), end.Y };
         break;
     case SelectionExpansion::Word:
-        start = _buffer->GetWordStart(start, _wordDelimiters);
-        end = _buffer->GetWordEnd(end, _wordDelimiters);
+        start = _activeBuffer().GetWordStart(start, _wordDelimiters);
+        end = _activeBuffer().GetWordEnd(end, _wordDelimiters);
         break;
     case SelectionExpansion::Char:
     default:
@@ -325,7 +325,7 @@ void Terminal::UpdateSelection(SelectionDirection direction, SelectionExpansion
             _scrollOffset -= amtBelowView;
         }
         _NotifyScrollEvent();
-        _buffer->GetRenderTarget().TriggerScroll();
+        _activeBuffer().GetRenderTarget().TriggerScroll();
     }
 }
 
@@ -334,22 +334,22 @@ void Terminal::_MoveByChar(SelectionDirection direction, COORD& pos)
     switch (direction)
     {
     case SelectionDirection::Left:
-        _buffer->GetSize().DecrementInBounds(pos);
-        pos = _buffer->GetGlyphStart(til::point{ pos }).to_win32_coord();
+        _activeBuffer().GetSize().DecrementInBounds(pos);
+        pos = _activeBuffer().GetGlyphStart(til::point{ pos }).to_win32_coord();
         break;
     case SelectionDirection::Right:
-        _buffer->GetSize().IncrementInBounds(pos);
-        pos = _buffer->GetGlyphEnd(til::point{ pos }).to_win32_coord();
+        _activeBuffer().GetSize().IncrementInBounds(pos);
+        pos = _activeBuffer().GetGlyphEnd(til::point{ pos }).to_win32_coord();
         break;
     case SelectionDirection::Up:
     {
-        const auto bufferSize{ _buffer->GetSize() };
+        const auto bufferSize{ _activeBuffer().GetSize() };
         pos = { pos.X, std::clamp(base::ClampSub<short, short>(pos.Y, 1).RawValue(), bufferSize.Top(), bufferSize.BottomInclusive()) };
         break;
     }
     case SelectionDirection::Down:
     {
-        const auto bufferSize{ _buffer->GetSize() };
+        const auto bufferSize{ _activeBuffer().GetSize() };
         pos = { pos.X, std::clamp(base::ClampAdd<short, short>(pos.Y, 1).RawValue(), bufferSize.Top(), bufferSize.BottomInclusive()) };
         break;
     }
@@ -361,19 +361,19 @@ void Terminal::_MoveByWord(SelectionDirection direction, COORD& pos)
     switch (direction)
     {
     case SelectionDirection::Left:
-        const auto wordStartPos{ _buffer->GetWordStart(pos, _wordDelimiters) };
-        if (_buffer->GetSize().CompareInBounds(_selection->pivot, pos) < 0)
+        const auto wordStartPos{ _activeBuffer().GetWordStart(pos, _wordDelimiters) };
+        if (_activeBuffer().GetSize().CompareInBounds(_selection->pivot, pos) < 0)
         {
             // If we're moving towards the pivot, move one more cell
             pos = wordStartPos;
-            _buffer->GetSize().DecrementInBounds(pos);
+            _activeBuffer().GetSize().DecrementInBounds(pos);
         }
         else if (wordStartPos == pos)
         {
             // already at the beginning of the current word,
             // move to the beginning of the previous word
-            _buffer->GetSize().DecrementInBounds(pos);
-            pos = _buffer->GetWordStart(pos, _wordDelimiters);
+            _activeBuffer().GetSize().DecrementInBounds(pos);
+            pos = _activeBuffer().GetWordStart(pos, _wordDelimiters);
         }
         else
         {
@@ -382,19 +382,19 @@ void Terminal::_MoveByWord(SelectionDirection direction, COORD& pos)
         }
         break;
     case SelectionDirection::Right:
-        const auto wordEndPos{ _buffer->GetWordEnd(pos, _wordDelimiters) };
-        if (_buffer->GetSize().CompareInBounds(pos, _selection->pivot) < 0)
+        const auto wordEndPos{ _activeBuffer().GetWordEnd(pos, _wordDelimiters) };
+        if (_activeBuffer().GetSize().CompareInBounds(pos, _selection->pivot) < 0)
         {
             // If we're moving towards the pivot, move one more cell
-            pos = _buffer->GetWordEnd(pos, _wordDelimiters);
-            _buffer->GetSize().IncrementInBounds(pos);
+            pos = _activeBuffer().GetWordEnd(pos, _wordDelimiters);
+            _activeBuffer().GetSize().IncrementInBounds(pos);
         }
         else if (wordEndPos == pos)
         {
             // already at the end of the current word,
             // move to the end of the next word
-            _buffer->GetSize().IncrementInBounds(pos);
-            pos = _buffer->GetWordEnd(pos, _wordDelimiters);
+            _activeBuffer().GetSize().IncrementInBounds(pos);
+            pos = _activeBuffer().GetWordEnd(pos, _wordDelimiters);
         }
         else
         {
@@ -404,18 +404,18 @@ void Terminal::_MoveByWord(SelectionDirection direction, COORD& pos)
         break;
     case SelectionDirection::Up:
         _MoveByChar(direction, pos);
-        pos = _buffer->GetWordStart(pos, _wordDelimiters);
+        pos = _activeBuffer().GetWordStart(pos, _wordDelimiters);
         break;
     case SelectionDirection::Down:
         _MoveByChar(direction, pos);
-        pos = _buffer->GetWordEnd(pos, _wordDelimiters);
+        pos = _activeBuffer().GetWordEnd(pos, _wordDelimiters);
         break;
     }
 }
 
 void Terminal::_MoveByViewport(SelectionDirection direction, COORD& pos)
 {
-    const auto bufferSize{ _buffer->GetSize() };
+    const auto bufferSize{ _activeBuffer().GetSize() };
     switch (direction)
     {
     case SelectionDirection::Left:
@@ -444,7 +444,7 @@ void Terminal::_MoveByViewport(SelectionDirection direction, COORD& pos)
 
 void Terminal::_MoveByBuffer(SelectionDirection direction, COORD& pos)
 {
-    const auto bufferSize{ _buffer->GetSize() };
+    const auto bufferSize{ _activeBuffer().GetSize() };
     switch (direction)
     {
     case SelectionDirection::Left:
@@ -489,7 +489,7 @@ const TextBuffer::TextAndColor Terminal::RetrieveSelectedTextFromBuffer(bool sin
     const auto includeCRLF = !singleLine || _blockSelection;
     const auto trimTrailingWhitespace = !singleLine && (!_blockSelection || _trimBlockSelection);
     const auto formatWrappedRows = _blockSelection;
-    return _buffer->GetText(includeCRLF, trimTrailingWhitespace, selectionRects, GetAttributeColors, formatWrappedRows);
+    return _activeBuffer().GetText(includeCRLF, trimTrailingWhitespace, selectionRects, GetAttributeColors, formatWrappedRows);
 }
 
 // Method Description:
@@ -502,7 +502,7 @@ COORD Terminal::_ConvertToBufferCell(const COORD viewportPos) const
 {
     const auto yPos = base::ClampedNumeric<short>(_VisibleStartIndex()) + viewportPos.Y;
     COORD bufferPos = { viewportPos.X, yPos };
-    _buffer->GetSize().Clamp(bufferPos);
+    _activeBuffer().GetSize().Clamp(bufferPos);
     return bufferPos;
 }
 

src/cascadia/TerminalCore/terminalrenderdata.cpp

@@ -25,7 +25,7 @@ COORD Terminal::GetTextBufferEndPosition() const noexcept
 
 const TextBuffer& Terminal::GetTextBuffer() noexcept
 {
-    return *_buffer;
+    return _activeBuffer();
 }
 
 const FontInfo& Terminal::GetFontInfo() noexcept
@@ -40,19 +40,19 @@ void Terminal::SetFontInfo(const FontInfo& fontInfo)
 
 COORD Terminal::GetCursorPosition() const noexcept
 {
-    const auto& cursor = _buffer->GetCursor();
+    const auto& cursor = _activeBuffer().GetCursor();
     return cursor.GetPosition();
 }
 
 bool Terminal::IsCursorVisible() const noexcept
 {
-    const auto& cursor = _buffer->GetCursor();
+    const auto& cursor = _activeBuffer().GetCursor();
     return cursor.IsVisible() && !cursor.IsPopupShown();
 }
 
 bool Terminal::IsCursorOn() const noexcept
 {
-    const auto& cursor = _buffer->GetCursor();
+    const auto& cursor = _activeBuffer().GetCursor();
     return cursor.IsOn();
 }
 
@@ -63,18 +63,18 @@ ULONG Terminal::GetCursorPixelWidth() const noexcept
 
 ULONG Terminal::GetCursorHeight() const noexcept
 {
-    return _buffer->GetCursor().GetSize();
+    return _activeBuffer().GetCursor().GetSize();
 }
 
 CursorType Terminal::GetCursorStyle() const noexcept
 {
-    return _buffer->GetCursor().GetType();
+    return _activeBuffer().GetCursor().GetType();
 }
 
 bool Terminal::IsCursorDoubleWidth() const
 {
-    const auto position = _buffer->GetCursor().GetPosition();
-    TextBufferTextIterator it(TextBufferCellIterator(*_buffer, position));
+    const auto position = _activeBuffer().GetCursor().GetPosition();
+    TextBufferTextIterator it(TextBufferCellIterator(_activeBuffer(), position));
     return IsGlyphFullWidth(*it);
 }
 
@@ -90,12 +90,12 @@ const bool Terminal::IsGridLineDrawingAllowed() noexcept
 
 const std::wstring Microsoft::Terminal::Core::Terminal::GetHyperlinkUri(uint16_t id) const noexcept
 {
-    return _buffer->GetHyperlinkUriFromId(id);
+    return _activeBuffer().GetHyperlinkUriFromId(id);
 }
 
 const std::wstring Microsoft::Terminal::Core::Terminal::GetHyperlinkCustomId(uint16_t id) const noexcept
 {
-    return _buffer->GetCustomIdFromId(id);
+    return _activeBuffer().GetCustomIdFromId(id);
 }
 
 // Method Description:
@@ -174,7 +174,7 @@ void Terminal::SelectNewRegion(const COORD coordStart, const COORD coordEnd)
 
     if (notifyScrollChange)
     {
-        _buffer->GetRenderTarget().TriggerScroll();
+        _activeBuffer().GetRenderTarget().TriggerScroll();
         _NotifyScrollEvent();
     }
 
@@ -227,5 +227,5 @@ const bool Terminal::IsUiaDataInitialized() const noexcept
     // when a screen reader requests it. However, the terminal might not be fully
     // initialized yet. So we use this to check if any crucial components of
     // UiaData are not yet initialized.
-    return !!_buffer;
+    return !!_mainBuffer;
 }