Add support for VT horizontal mouse wheel events (#19248)

This adds support for horizontal mouse wheel events (`WM_MOUSEHWHEEL`).
With this change, applications running in the terminal can now receive
and respond to horizontal scroll inputs from the mouse/trackpad.

Closes #19245
Closes #10329

src/cascadia/TerminalControl/ControlInteractivity.cpp

@@ -485,7 +485,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     // - modifiers: The modifiers pressed during this event, in the form of a VirtualKeyModifiers
     // - delta: the mouse wheel delta that triggered this event.
     bool ControlInteractivity::MouseWheel(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers,
-                                          const int32_t delta,
+                                          const Core::Point delta,
                                           const Core::Point pixelPosition,
                                           const Control::MouseButtonState buttonState)
     {
@@ -506,9 +506,9 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             // PointerPoint to work with. So, we're just going to do a
             // mousewheel event manually
             return _sendMouseEventHelper(terminalPosition,
-                                         WM_MOUSEWHEEL,
+                                         delta.Y != 0 ? WM_MOUSEWHEEL : WM_MOUSEHWHEEL,
                                          modifiers,
-                                         ::base::saturated_cast<short>(delta),
+                                         ::base::saturated_cast<short>(delta.Y != 0 ? delta.Y : delta.X),
                                          buttonState);
         }
 
@@ -517,15 +517,15 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         if (ctrlPressed && shiftPressed && _core->Settings().ScrollToChangeOpacity())
         {
-            _mouseTransparencyHandler(delta);
+            _mouseTransparencyHandler(delta.Y);
         }
         else if (ctrlPressed && !shiftPressed && _core->Settings().ScrollToZoom())
         {
-            _mouseZoomHandler(delta);
+            _mouseZoomHandler(delta.Y);
         }
         else
         {
-            _mouseScrollHandler(delta, pixelPosition, WI_IsFlagSet(buttonState, MouseButtonState::IsLeftButtonDown));
+            _mouseScrollHandler(delta.Y, pixelPosition, WI_IsFlagSet(buttonState, MouseButtonState::IsLeftButtonDown));
         }
         return false;
     }
@@ -659,7 +659,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         return _core->IsVtMouseModeEnabled();
     }
 
-    bool ControlInteractivity::_shouldSendAlternateScroll(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers, const int32_t delta)
+    bool ControlInteractivity::_shouldSendAlternateScroll(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers, const Core::Point delta)
     {
         // If the user is holding down Shift, suppress mouse events
         // TODO GH#4875: disable/customize this functionality
@@ -667,7 +667,14 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         {
             return false;
         }
-        return _core->ShouldSendAlternateScroll(WM_MOUSEWHEEL, delta);
+        if (delta.Y != 0)
+        {
+            return _core->ShouldSendAlternateScroll(WM_MOUSEWHEEL, delta.Y);
+        }
+        else
+        {
+            return _core->ShouldSendAlternateScroll(WM_MOUSEHWHEEL, delta.X);
+        }
     }
 
     // Method Description:

src/cascadia/TerminalControl/ControlInteractivity.h

@@ -74,7 +74,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         void TouchReleased();
 
         bool MouseWheel(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers,
-                        const int32_t delta,
+                        const Core::Point delta,
                         const Core::Point pixelPosition,
                         const Control::MouseButtonState state);
 
@@ -153,7 +153,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         void _hyperlinkHandler(const std::wstring_view uri);
         bool _canSendVTMouseInput(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers);
-        bool _shouldSendAlternateScroll(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers, const int32_t delta);
+        bool _shouldSendAlternateScroll(const ::Microsoft::Terminal::Core::ControlKeyStates modifiers, const Core::Point delta);
 
         til::point _getTerminalPosition(const til::point pixelPosition, bool roundToNearestCell);
 

src/cascadia/TerminalControl/ControlInteractivity.idl

@@ -60,7 +60,7 @@ namespace Microsoft.Terminal.Control
         void TouchReleased();
 
         Boolean MouseWheel(Microsoft.Terminal.Core.ControlKeyStates modifiers,
-                           Int32 delta,
+                           Microsoft.Terminal.Core.Point delta,
                            Microsoft.Terminal.Core.Point pixelPosition,
                            MouseButtonState state);
 

src/cascadia/TerminalControl/IMouseWheelListener.idl

@@ -11,6 +11,6 @@ namespace Microsoft.Terminal.Control
     [uuid("65b8b8c5-988f-43ff-aba9-e89368da1598")]
     interface IMouseWheelListener
     {
-        Boolean OnMouseWheel(Windows.Foundation.Point coord, Int32 delta, Boolean leftButtonDown, Boolean midButtonDown, Boolean rightButtonDown);
+        Boolean OnMouseWheel(Windows.Foundation.Point coord, Microsoft.Terminal.Core.Point delta, Boolean leftButtonDown, Boolean midButtonDown, Boolean rightButtonDown);
     }
 }

src/cascadia/TerminalControl/TermControl.cpp

@@ -2160,15 +2160,11 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         RestorePointerCursor.raise(*this, nullptr);
 
         const auto point = args.GetCurrentPoint(*this);
-        // GH#10329 - we don't need to handle horizontal scrolls. Only vertical ones.
+        auto delta = point.Properties().MouseWheelDelta();
-        // So filter out the horizontal ones.
-        if (point.Properties().IsHorizontalMouseWheel())
-        {
-            return;
-        }
-
         auto result = _interactivity.MouseWheel(ControlKeyStates{ args.KeyModifiers() },
-                                                point.Properties().MouseWheelDelta(),
+                                                point.Properties().IsHorizontalMouseWheel() ?
+                                                    Core::Point{ delta, 0 } :
+                                                    Core::Point{ 0, delta },
                                                 _toTerminalOrigin(point.Position()),
                                                 TermControl::GetPressedMouseButtons(point));
         if (result)
@@ -2188,7 +2184,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     // - delta: the mouse wheel delta that triggered this event.
     // - state: the state for each of the mouse buttons individually (pressed/unpressed)
     bool TermControl::OnMouseWheel(const Windows::Foundation::Point location,
-                                   const int32_t delta,
+                                   const Core::Point delta,
                                    const bool leftButtonDown,
                                    const bool midButtonDown,
                                    const bool rightButtonDown)

src/cascadia/TerminalControl/TermControl.h

@@ -148,7 +148,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         bool OnDirectKeyEvent(const uint32_t vkey, const uint8_t scanCode, const bool down);
 
-        bool OnMouseWheel(const Windows::Foundation::Point location, const int32_t delta, const bool leftButtonDown, const bool midButtonDown, const bool rightButtonDown);
+        bool OnMouseWheel(const Windows::Foundation::Point location, const winrt::Microsoft::Terminal::Core::Point delta, const bool leftButtonDown, const bool midButtonDown, const bool rightButtonDown);
 
         ~TermControl();
 

src/cascadia/UnitTests_Control/ControlInteractivityTests.cpp

@@ -170,7 +170,7 @@ namespace ControlUnitTests
 
             // The mouse location and buttons don't matter here.
             interactivity->MouseWheel(modifiers,
-                                      30,
+                                      Core::Point{ 0, 30 },
                                       Core::Point{ 0, 0 },
                                       buttonState);
         }
@@ -188,7 +188,7 @@ namespace ControlUnitTests
 
             // The mouse location and buttons don't matter here.
             interactivity->MouseWheel(modifiers,
-                                      -30,
+                                      Core::Point{ 0, -30 },
                                       Core::Point{ 0, 0 },
                                       buttonState);
         }
@@ -245,7 +245,7 @@ namespace ControlUnitTests
         expectedTop = 20;
 
         interactivity->MouseWheel(modifiers,
-                                  WHEEL_DELTA,
+                                  Core::Point{ 0, WHEEL_DELTA },
                                   Core::Point{ 0, 0 },
                                   buttonState);
 
@@ -254,18 +254,18 @@ namespace ControlUnitTests
         {
             expectedTop--;
             interactivity->MouseWheel(modifiers,
-                                      WHEEL_DELTA,
+                                      Core::Point{ 0, WHEEL_DELTA },
                                       Core::Point{ 0, 0 },
                                       buttonState);
         }
         Log::Comment(L"Scrolling up more should do nothing");
         expectedTop = 0;
         interactivity->MouseWheel(modifiers,
-                                  WHEEL_DELTA,
+                                  Core::Point{ 0, WHEEL_DELTA },
                                   Core::Point{ 0, 0 },
                                   buttonState);
         interactivity->MouseWheel(modifiers,
-                                  WHEEL_DELTA,
+                                  Core::Point{ 0, WHEEL_DELTA },
                                   Core::Point{ 0, 0 },
                                   buttonState);
 
@@ -275,7 +275,7 @@ namespace ControlUnitTests
             Log::Comment(NoThrowString().Format(L"---scroll down #%d---", i));
             expectedTop++;
             interactivity->MouseWheel(modifiers,
-                                      -WHEEL_DELTA,
+                                      Core::Point{ 0, -WHEEL_DELTA },
                                       Core::Point{ 0, 0 },
                                       buttonState);
             Log::Comment(NoThrowString().Format(L"internal scrollbar pos:%f", interactivity->_internalScrollbarPosition));
@@ -283,11 +283,11 @@ namespace ControlUnitTests
         Log::Comment(L"Scrolling down more should do nothing");
         expectedTop = 21;
         interactivity->MouseWheel(modifiers,
-                                  -WHEEL_DELTA,
+                                  Core::Point{ 0, -WHEEL_DELTA },
                                   Core::Point{ 0, 0 },
                                   buttonState);
         interactivity->MouseWheel(modifiers,
-                                  -WHEEL_DELTA,
+                                  Core::Point{ 0, -WHEEL_DELTA },
                                   Core::Point{ 0, 0 },
                                   buttonState);
     }
@@ -444,7 +444,7 @@ namespace ControlUnitTests
 
         Log::Comment(L"Scroll up a line, with the left mouse button selected");
         interactivity->MouseWheel(modifiers,
-                                  WHEEL_DELTA,
+                                  Core::Point{ 0, WHEEL_DELTA },
                                   cursorPosition1.to_core_point(),
                                   leftMouseDown);
 
@@ -492,55 +492,55 @@ namespace ControlUnitTests
         const Core::Point mousePos{ 0, 0 };
         Control::MouseButtonState state{};
 
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 1/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 1/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
 
         Log::Comment(L"Scroll up 4 more times. Once we're at 3/5 scrolls, "
                      L"we'll round the internal scrollbar position to scrolling to the next row.");
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 2/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 2/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 3/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 3/5
         VERIFY_ARE_EQUAL(20, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 4/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 4/5
         VERIFY_ARE_EQUAL(20, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 5/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 5/5
         VERIFY_ARE_EQUAL(20, core->ScrollOffset());
 
         Log::Comment(L"Jump to line 5, so we can scroll down from there.");
         interactivity->UpdateScrollbar(5);
         VERIFY_ARE_EQUAL(5, core->ScrollOffset());
         Log::Comment(L"Scroll down 5 times, at which point we should accumulate a whole row of delta.");
-        interactivity->MouseWheel(modifiers, -delta, mousePos, state); // 1/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, -delta }, mousePos, state); // 1/5
         VERIFY_ARE_EQUAL(5, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, -delta, mousePos, state); // 2/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, -delta }, mousePos, state); // 2/5
         VERIFY_ARE_EQUAL(5, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, -delta, mousePos, state); // 3/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, -delta }, mousePos, state); // 3/5
         VERIFY_ARE_EQUAL(6, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, -delta, mousePos, state); // 4/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, -delta }, mousePos, state); // 4/5
         VERIFY_ARE_EQUAL(6, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, -delta, mousePos, state); // 5/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, -delta }, mousePos, state); // 5/5
         VERIFY_ARE_EQUAL(6, core->ScrollOffset());
 
         Log::Comment(L"Jump to the bottom.");
         interactivity->UpdateScrollbar(21);
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
         Log::Comment(L"Scroll a bit, then emit a line of text. We should reset our internal scroll position.");
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 1/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 1/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 2/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 2/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
 
         conn->WriteInput(winrt_wstring_to_array_view(L"Foo\r\n"));
         VERIFY_ARE_EQUAL(22, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 1/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 1/5
         VERIFY_ARE_EQUAL(22, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 2/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 2/5
         VERIFY_ARE_EQUAL(22, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 3/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 3/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 4/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 4/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
-        interactivity->MouseWheel(modifiers, delta, mousePos, state); // 5/5
+        interactivity->MouseWheel(modifiers, Core::Point{ 0, delta }, mousePos, state); // 5/5
         VERIFY_ARE_EQUAL(21, core->ScrollOffset());
     }
 
@@ -709,7 +709,7 @@ namespace ControlUnitTests
         {
             expectedTop--;
             interactivity->MouseWheel(modifiers,
-                                      WHEEL_DELTA,
+                                      Core::Point{ 0, WHEEL_DELTA },
                                       Core::Point{ 0, 0 },
                                       noMouseDown);
         }

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -745,7 +745,7 @@ void AppHost::_RaiseVisualBell(const winrt::Windows::Foundation::IInspectable&,
 // - delta: the wheel delta that triggered this event.
 // Return Value:
 // - <none>
-void AppHost::_WindowMouseWheeled(const winrt::Windows::Foundation::Point coord, const int32_t delta)
+void AppHost::_WindowMouseWheeled(const winrt::Windows::Foundation::Point coord, const winrt::Microsoft::Terminal::Core::Point delta)
 {
     if (_windowLogic)
     {

src/cascadia/WindowsTerminal/AppHost.h

@@ -73,7 +73,7 @@ private:
 
     void _RaiseVisualBell(const winrt::Windows::Foundation::IInspectable& sender,
                           const winrt::Windows::Foundation::IInspectable& arg);
-    void _WindowMouseWheeled(const winrt::Windows::Foundation::Point coord, const int32_t delta);
+    void _WindowMouseWheeled(const winrt::Windows::Foundation::Point coord, const winrt::Microsoft::Terminal::Core::Point delta);
     void _WindowActivated(bool activated);
     void _WindowMoved();
 

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -595,6 +595,7 @@ void IslandWindow::_OnGetMinMaxInfo(const WPARAM /*wParam*/, const LPARAM lParam
         WindowCloseButtonClicked.raise();
         return 0;
     }
+    case WM_MOUSEHWHEEL:
     case WM_MOUSEWHEEL:
         try
         {
@@ -623,7 +624,11 @@ void IslandWindow::_OnGetMinMaxInfo(const WPARAM /*wParam*/, const LPARAM lParam
             const auto scale = GetCurrentDpiScale();
             const winrt::Windows::Foundation::Point real{ relative.x / scale, relative.y / scale };
 
-            const auto wheelDelta = static_cast<short>(HIWORD(wparam));
+            winrt::Microsoft::Terminal::Core::Point wheelDelta{ 0, static_cast<int32_t>(HIWORD(wparam)) };
+            if (message == WM_MOUSEHWHEEL)
+            {
+                std::swap(wheelDelta.X, wheelDelta.Y);
+            }
 
             // Raise an event, so any listeners can handle the mouse wheel event manually.
             MouseScrolled.raise(real, wheelDelta);

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -74,7 +74,7 @@ public:
 
     til::event<winrt::delegate<>> DragRegionClicked;
     til::event<winrt::delegate<>> WindowCloseButtonClicked;
-    til::event<winrt::delegate<void(winrt::Windows::Foundation::Point, int32_t)>> MouseScrolled;
+    til::event<winrt::delegate<void(winrt::Windows::Foundation::Point, winrt::Microsoft::Terminal::Core::Point)>> MouseScrolled;
     til::event<winrt::delegate<void(bool)>> WindowActivated;
     til::event<winrt::delegate<void()>> NotifyNotificationIconPressed;
     til::event<winrt::delegate<void()>> NotifyWindowHidden;

src/interactivity/win32/windowio.cpp

@@ -567,7 +567,7 @@ BOOL HandleMouseEvent(const SCREEN_INFORMATION& ScreenInfo,
     if (!fShiftPressed && !pSelection->IsInSelectingState())
     {
         short sDelta = 0;
-        if (Message == WM_MOUSEWHEEL)
+        if (Message == WM_MOUSEWHEEL || Message == WM_MOUSEHWHEEL)
         {
             sDelta = GET_WHEEL_DELTA_WPARAM(wParam);
         }

src/terminal/adapter/ut_adapter/MouseInputTest.cpp

@@ -127,10 +127,13 @@ public:
             wch = L'!';
             break;
         case WM_MOUSEWHEEL:
-        case WM_MOUSEHWHEEL:
             Log::Comment(NoThrowString().Format(L"MOUSEWHEEL"));
             wch = L'`' + (sScrollDelta > 0 ? 0 : 1);
             break;
+        case WM_MOUSEHWHEEL:
+            Log::Comment(NoThrowString().Format(L"MOUSEHWHEEL"));
+            wch = L'b' + (sScrollDelta > 0 ? 1 : 0);
+            break;
         case WM_MOUSEMOVE:
         default:
             Log::Comment(NoThrowString().Format(L"DEFAULT"));
@@ -168,9 +171,11 @@ public:
             result = 3 + 0x20; // we add 0x20 to hover events, which are all encoded as WM_MOUSEMOVE events
             break;
         case WM_MOUSEWHEEL:
-        case WM_MOUSEHWHEEL:
             result = (sScrollDelta > 0 ? 64 : 65);
             break;
+        case WM_MOUSEHWHEEL:
+            result = (sScrollDelta > 0 ? 67 : 66);
+            break;
         default:
             result = 0;
             break;
@@ -582,6 +587,12 @@ public:
         Log::Comment(L"Test mouse wheel scrolling down");
         VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1B[B"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, -WHEEL_DELTA, {}));
 
+        Log::Comment(L"Test mouse wheel scrolling right");
+        VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1B[C"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEHWHEEL, noModifierKeys, WHEEL_DELTA, {}));
+
+        Log::Comment(L"Test mouse wheel scrolling left");
+        VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1B[D"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEHWHEEL, noModifierKeys, -WHEEL_DELTA, {}));
+
         Log::Comment(L"Enable cursor keys mode");
         mouseInput.SetInputMode(TerminalInput::Mode::CursorKey, true);
 
@@ -591,6 +602,12 @@ public:
         Log::Comment(L"Test mouse wheel scrolling down");
         VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1BOB"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, -WHEEL_DELTA, {}));
 
+        Log::Comment(L"Test mouse wheel scrolling right");
+        VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1BOC"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEHWHEEL, noModifierKeys, WHEEL_DELTA, {}));
+
+        Log::Comment(L"Test mouse wheel scrolling left");
+        VERIFY_ARE_EQUAL(TerminalInput::MakeOutput(L"\x1BOD"), mouseInput.HandleMouse({ 0, 0 }, WM_MOUSEHWHEEL, noModifierKeys, -WHEEL_DELTA, {}));
+
         Log::Comment(L"Confirm no effect when scroll mode is disabled");
         mouseInput.UseAlternateScreenBuffer();
         mouseInput.SetInputMode(TerminalInput::Mode::AlternateScroll, false);

src/terminal/input/mouseInput.cpp

@@ -163,9 +163,11 @@ static constexpr wchar_t _windowsButtonToXEncoding(const unsigned int button,
         xvalue = 1;
         break;
     case WM_MOUSEWHEEL:
-    case WM_MOUSEHWHEEL:
         xvalue = delta > 0 ? 0x40 : 0x41;
         break;
+    case WM_MOUSEHWHEEL:
+        xvalue = delta > 0 ? 0x43 : 0x42;
+        break;
     default:
         xvalue = 0;
         break;
@@ -221,9 +223,11 @@ static constexpr int _windowsButtonToSGREncoding(const unsigned int button,
         xvalue = 3;
         break;
     case WM_MOUSEWHEEL:
-    case WM_MOUSEHWHEEL:
         xvalue = delta > 0 ? 0x40 : 0x41;
         break;
+    case WM_MOUSEHWHEEL:
+        xvalue = delta > 0 ? 0x43 : 0x42;
+        break;
     default:
         xvalue = 0;
         break;
@@ -378,7 +382,7 @@ TerminalInput::OutputType TerminalInput::HandleMouse(const til::point position,
 
     if (ShouldSendAlternateScroll(button, delta))
     {
-        return _makeAlternateScrollOutput(delta);
+        return _makeAlternateScrollOutput(button, delta);
     }
 
     return {};
@@ -493,7 +497,9 @@ bool TerminalInput::ShouldSendAlternateScroll(const unsigned int button, const s
 // - Sends a sequence to the input corresponding to cursor up / down depending on the sScrollDelta.
 // Parameters:
 // - delta: The scroll wheel delta of the input event
-TerminalInput::OutputType TerminalInput::_makeAlternateScrollOutput(const short delta) const
+TerminalInput::OutputType TerminalInput::_makeAlternateScrollOutput(const unsigned int button, const short delta) const
+{
+    if (button == WM_MOUSEWHEEL)
     {
         if (delta > 0)
         {
@@ -504,3 +510,19 @@ TerminalInput::OutputType TerminalInput::_makeAlternateScrollOutput(const short
             return MakeOutput(_keyMap.at(VK_DOWN));
         }
     }
+    else if (button == WM_MOUSEHWHEEL)
+    {
+        if (delta > 0)
+        {
+            return MakeOutput(_keyMap.at(VK_RIGHT));
+        }
+        else
+        {
+            return MakeOutput(_keyMap.at(VK_LEFT));
+        }
+    }
+    else
+    {
+        return {};
+    }
+}

src/terminal/input/terminalInput.hpp

@@ -111,7 +111,7 @@ namespace Microsoft::Console::VirtualTerminal
         [[nodiscard]] OutputType _GenerateUtf8Sequence(til::point position, unsigned int button, bool isHover, short modifierKeyState, short delta);
         [[nodiscard]] OutputType _GenerateSGRSequence(til::point position, unsigned int button, bool isRelease, bool isHover, short modifierKeyState, short delta);
 
-        [[nodiscard]] OutputType _makeAlternateScrollOutput(short delta) const;
+        [[nodiscard]] OutputType _makeAlternateScrollOutput(unsigned int button, short delta) const;
 
         static constexpr unsigned int s_GetPressedButton(const MouseButtonState state) noexcept;
 #pragma endregion

src/terminal/parser/InputStateMachineEngine.cpp

@@ -897,6 +897,22 @@ bool InputStateMachineEngine::_UpdateSGRMouseButtonState(const VTID id,
         eventFlags |= MOUSE_WHEELED;
         break;
     }
+    case CsiMouseButtonCodes::ScrollLeft:
+    {
+        // set high word to proper scroll direction
+        // scroll intensity is assumed to be constant value
+        buttonState |= SCROLL_DELTA_BACKWARD;
+        eventFlags |= MOUSE_HWHEELED;
+        break;
+    }
+    case CsiMouseButtonCodes::ScrollRight:
+    {
+        // set high word to proper scroll direction
+        // scroll intensity is assumed to be constant value
+        buttonState |= SCROLL_DELTA_FORWARD;
+        eventFlags |= MOUSE_HWHEELED;
+        break;
+    }
     case CsiMouseButtonCodes::Released:
         // hover event, we still want to send these but we don't
         // need to do anything special here, so just break

src/terminal/parser/InputStateMachineEngine.hpp

@@ -111,6 +111,8 @@ namespace Microsoft::Console::VirtualTerminal
         Released = 3,
         ScrollForward = 4,
         ScrollBack = 5,
+        ScrollLeft = 6,
+        ScrollRight = 7,
     };
 
     constexpr unsigned short CsiMouseModifierCode_Drag = 32;

src/terminal/parser/ut_parser/InputEngineTest.cpp

@@ -1196,6 +1196,8 @@ void InputEngineTest::SGRMouseTest_Scroll()
         //  TEST INPUT                                                                             EXPECTED OUTPUT
         {   { CsiMouseButtonCodes::ScrollForward, 0, { 1, 1 }, CsiActionCodes::MouseDown },        { SCROLL_DELTA_FORWARD,  0, { 0, 0 }, MOUSE_WHEELED  } },
         {   { CsiMouseButtonCodes::ScrollBack,    0, { 1, 1 }, CsiActionCodes::MouseDown },        { SCROLL_DELTA_BACKWARD, 0, { 0, 0 }, MOUSE_WHEELED  } },
+        {   { CsiMouseButtonCodes::ScrollLeft,    0, { 1, 1 }, CsiActionCodes::MouseDown },        { SCROLL_DELTA_BACKWARD, 0, { 0, 0 }, MOUSE_HWHEELED } },
+        {   { CsiMouseButtonCodes::ScrollRight,   0, { 1, 1 }, CsiActionCodes::MouseDown },        { SCROLL_DELTA_FORWARD,  0, { 0, 0 }, MOUSE_HWHEELED } },
     };
     // clang-format on
     VerifySGRMouseData(testData);