ConPTY: Emit DSR CPR on resize (#19089)

This will help terminals with a reflow behavior unlike
the one implemented in ConPTY, such as VS Code.

Closes #18725

## Validation Steps Performed
* Tested under a debugger ✅
* Use PowerShell 5 and reflow lines in the ConPTY buffer until they're
  pushed outside the top viewport. Then type something in the prompt.
  Cursor is in a consistent position, even if slightly off. ✅

Author: lhecker

src/host/PtySignalInputThread.cpp

@@ -184,6 +184,9 @@ void PtySignalInputThread::_DoResizeWindow(const ResizeWindowData& data)
     }
 
     _api.ResizeWindow(data.sx, data.sy);
+
+    auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+    gci.GetVtIo()->RequestCursorPositionFromTerminal();
 }
 
 void PtySignalInputThread::_DoClearBuffer(const bool keepCursorRow) const

src/host/VtInputThread.cpp

@@ -21,13 +21,13 @@ using namespace Microsoft::Console::VirtualTerminal;
 // - hPipe - a handle to the file representing the read end of the VT pipe.
 // - inheritCursor - a bool indicating if the state machine should expect a
 //      cursor positioning sequence. See MSFT:15681311.
-VtInputThread::VtInputThread(_In_ wil::unique_hfile hPipe, const bool inheritCursor) :
+VtInputThread::VtInputThread(_In_ wil::unique_hfile hPipe, std::function<void()> capturedCPR) :
     _hFile{ std::move(hPipe) }
 {
     THROW_HR_IF(E_HANDLE, _hFile.get() == INVALID_HANDLE_VALUE);
 
     auto dispatch = std::make_unique<InteractDispatch>();
-    auto engine = std::make_unique<InputStateMachineEngine>(std::move(dispatch), inheritCursor);
+    auto engine = std::make_unique<InputStateMachineEngine>(std::move(dispatch), std::move(capturedCPR));
     _pInputStateMachine = std::make_unique<StateMachine>(std::move(engine));
 }
 
@@ -185,8 +185,7 @@ void VtInputThread::_InputThread()
     return S_OK;
 }
 
-til::enumset<DeviceAttribute, uint64_t> VtInputThread::WaitUntilDA1(DWORD timeout) const noexcept
+InputStateMachineEngine& VtInputThread::GetInputStateMachineEngine() const noexcept
 {
-    const auto& engine = static_cast<InputStateMachineEngine&>(_pInputStateMachine->Engine());
-    return engine.WaitUntilDA1(timeout);
+    return static_cast<InputStateMachineEngine&>(_pInputStateMachine->Engine());
 }

src/host/VtInputThread.hpp

@@ -20,16 +20,17 @@ namespace Microsoft::Console
 {
     namespace VirtualTerminal
     {
+        class InputStateMachineEngine;
         enum class DeviceAttribute : uint64_t;
     }
 
     class VtInputThread
     {
     public:
-        VtInputThread(_In_ wil::unique_hfile hPipe, const bool inheritCursor);
+        VtInputThread(_In_ wil::unique_hfile hPipe, std::function<void()> capturedCPR = nullptr);
 
         [[nodiscard]] HRESULT Start();
-        til::enumset<VirtualTerminal::DeviceAttribute, uint64_t> WaitUntilDA1(DWORD timeout) const noexcept;
+        VirtualTerminal::InputStateMachineEngine& GetInputStateMachineEngine() const noexcept;
 
     private:
         static DWORD WINAPI StaticVtInputThreadProc(_In_ LPVOID lpParameter);

src/host/VtIo.cpp

@@ -11,6 +11,7 @@
 #include "output.h" // CloseConsoleProcessState
 #include "../interactivity/inc/ServiceLocator.hpp"
 #include "../renderer/base/renderer.hpp"
+#include "../terminal/parser/InputStateMachineEngine.hpp"
 #include "../types/inc/CodepointWidthDetector.hpp"
 #include "../types/inc/utils.hpp"
 
@@ -155,7 +156,9 @@ bool VtIo::IsUsingVt() const
     {
         if (IsValidHandle(_hInput.get()))
         {
-            _pVtInputThread = std::make_unique<VtInputThread>(std::move(_hInput), _lookingForCursorPosition);
+            _pVtInputThread = std::make_unique<VtInputThread>(std::move(_hInput), [this]() {
+                _cursorPositionReportReceived();
+            });
         }
     }
     CATCH_RETURN();
@@ -177,6 +180,7 @@ bool VtIo::IsUsingVt() const
             // wait for the DA1 response below and effectively wait for both.
             if (_lookingForCursorPosition)
             {
+                _pVtInputThread->GetInputStateMachineEngine().CaptureNextCPR();
                 writer.WriteUTF8("\x1b[6n"); // Cursor Position Report (DSR CPR)
             }
 
@@ -197,7 +201,7 @@ bool VtIo::IsUsingVt() const
             // Allow the input thread to momentarily gain the console lock.
             auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
             const auto suspension = gci.SuspendLock();
-            _deviceAttributes = _pVtInputThread->WaitUntilDA1(3000);
+            _deviceAttributes = _pVtInputThread->GetInputStateMachineEngine().WaitUntilDA1(3000);
         }
     }
 
@@ -226,6 +230,35 @@ bool VtIo::IsUsingVt() const
     return S_OK;
 }
 
+void VtIo::RequestCursorPositionFromTerminal()
+{
+    if (_lookingForCursorPosition)
+    {
+        // By delaying sending another DSR CPR until we received a response to the previous one,
+        // we debounce our requests to the terminal. We don't want to flood it unnecessarily.
+        _scheduleAnotherCPR = true;
+        return;
+    }
+
+    _lookingForCursorPosition = true;
+    _pVtInputThread->GetInputStateMachineEngine().CaptureNextCPR();
+
+    Writer writer{ this };
+    writer.WriteUTF8("\x1b[6n"); // Cursor Position Report (DSR CPR)
+    writer.Submit();
+}
+
+void VtIo::_cursorPositionReportReceived()
+{
+    _lookingForCursorPosition = false;
+
+    if (_scheduleAnotherCPR)
+    {
+        _scheduleAnotherCPR = false;
+        RequestCursorPositionFromTerminal();
+    }
+}
+
 void VtIo::SetDeviceAttributes(const til::enumset<DeviceAttribute, uint64_t> attributes) noexcept
 {
     _deviceAttributes = attributes;

src/host/VtIo.hpp

@@ -61,6 +61,7 @@ namespace Microsoft::Console::VirtualTerminal
         bool IsUsingVt() const;
         [[nodiscard]] HRESULT StartIfNeeded();
 
+        void RequestCursorPositionFromTerminal();
         void SetDeviceAttributes(til::enumset<DeviceAttribute, uint64_t> attributes) noexcept;
         til::enumset<DeviceAttribute, uint64_t> GetDeviceAttributes() const noexcept;
         void SendCloseEvent();
@@ -77,7 +78,7 @@ namespace Microsoft::Console::VirtualTerminal
         };
 
         [[nodiscard]] HRESULT _Initialize(const HANDLE InHandle, const HANDLE OutHandle, _In_opt_ const HANDLE SignalHandle);
-
+        void _cursorPositionReportReceived();
         void _uncork();
         void _flushNow();
 
@@ -105,6 +106,7 @@ namespace Microsoft::Console::VirtualTerminal
 
         State _state = State::Uninitialized;
         bool _lookingForCursorPosition = false;
+        bool _scheduleAnotherCPR = false;
         bool _closeEventSent = false;
         int _corked = 0;
 

src/terminal/parser/InputStateMachineEngine.cpp

@@ -89,14 +89,24 @@ static bool operator==(const Ss3ToVkey& pair, const Ss3ActionCodes code) noexcep
     return pair.action == code;
 }
 
-InputStateMachineEngine::InputStateMachineEngine(std::unique_ptr<IInteractDispatch> pDispatch, const bool lookingForDSR) :
-    _pDispatch(std::move(pDispatch)),
-    _lookingForDSR(lookingForDSR),
-    _doubleClickTime(std::chrono::milliseconds(GetDoubleClickTime()))
+InputStateMachineEngine::InputStateMachineEngine(std::unique_ptr<IInteractDispatch> pDispatch, std::function<void()> capturedCPR) :
+    _pDispatch{ std::move(pDispatch) },
+    _capturedCPR{ std::move(capturedCPR) },
+    _doubleClickTime{ std::chrono::milliseconds(GetDoubleClickTime()) }
 {
     THROW_HR_IF_NULL(E_INVALIDARG, _pDispatch.get());
 }
 
+IInteractDispatch& InputStateMachineEngine::GetDispatch() const noexcept
+{
+    return *_pDispatch.get();
+}
+
+void InputStateMachineEngine::CaptureNextCPR() noexcept
+{
+    _lookingForCPR = true;
+}
+
 til::enumset<DeviceAttribute, uint64_t> InputStateMachineEngine::WaitUntilDA1(DWORD timeout) const noexcept
 {
     uint64_t val = 0;
@@ -413,13 +423,19 @@ bool InputStateMachineEngine::ActionCsiDispatch(const VTID id, const VTParameter
         // The F3 case is special - it shares a code with the DeviceStatusResponse.
         // If we're looking for that response, then do that, and break out.
         // Else, fall though to the _GetCursorKeysModifierState handler.
-        if (_lookingForDSR)
+        if (_lookingForCPR)
         {
-            _pDispatch->MoveCursor(parameters.at(0), parameters.at(1));
-            // Right now we're only looking for on initial cursor
-            //      position response. After that, only look for F3.
-            _lookingForDSR = false;
-            return true;
+            _lookingForCPR = false;
+            _capturedCPR();
+
+            const auto y = parameters.at(0).value();
+            const auto x = parameters.at(1).value();
+
+            if (y > 0 && x > 0)
+            {
+                _pDispatch->MoveCursor(y, x);
+                return true;
+            }
         }
         // Heuristic: If the hosting terminal used the win32 input mode, chances are high
         // that this is a CPR requested by the terminal application as opposed to a F3 key.
@@ -491,10 +507,6 @@ bool InputStateMachineEngine::ActionCsiDispatch(const VTID id, const VTParameter
 
             _deviceAttributes.fetch_or(attributes.bits(), std::memory_order_relaxed);
             til::atomic_notify_all(_deviceAttributes);
-
-            // VtIo first sends a DSR CPR and then a DA1 request.
-            // If we encountered a DA1 response here, the DSR request is definitely done now.
-            _lookingForDSR = false;
             return true;
         }
         return false;

src/terminal/parser/InputStateMachineEngine.hpp

@@ -159,8 +159,10 @@ namespace Microsoft::Console::VirtualTerminal
     class InputStateMachineEngine : public IStateMachineEngine
     {
     public:
-        InputStateMachineEngine(std::unique_ptr<IInteractDispatch> pDispatch, const bool lookingForDSR = false);
+        InputStateMachineEngine(std::unique_ptr<IInteractDispatch> pDispatch, std::function<void()> capturedCPR = nullptr);
 
+        IInteractDispatch& GetDispatch() const noexcept;
+        void CaptureNextCPR() noexcept;
         til::enumset<DeviceAttribute, uint64_t> WaitUntilDA1(DWORD timeout) const noexcept;
 
         bool EncounteredWin32InputModeSequence() const noexcept override;
@@ -189,7 +191,8 @@ namespace Microsoft::Console::VirtualTerminal
     private:
         const std::unique_ptr<IInteractDispatch> _pDispatch;
         std::atomic<uint64_t> _deviceAttributes{ 0 };
-        bool _lookingForDSR = false;
+        bool _lookingForCPR = false;
+        std::function<void()> _capturedCPR;
         bool _encounteredWin32InputModeSequence = false;
         bool _expectingStringTerminator = false;
         DWORD _mouseButtonState = 0;