wpf: add support for VT mouse mode (#5375)

## Summary of the Pull Request

This pull request ports the VT mouse code from TermControl to WpfTerminalControl. Our WPF control is a lot closer to Win32 than to Xaml, so our mouse event handler looks _nothing_ like the one that we got from Xaml. We can pass events through almost directly, because the window message handling in the mouse input code actually came from _conhost_. It's awesome.

Neither TermControl nor conhost pass hover events through when the control isn't focused, so I wired up focus events to make sure we acted the same.

Just like Terminal and conhost, mouse events are suppressed when <kbd>Shift</kbd> is held.

## Validation Steps Performed
Tested with MC, and tested by manually engaging SGR events in an Echo terminal.

![image](https://user-images.githubusercontent.com/14316954/79417901-2f976a00-7f68-11ea-97e9-c053cbed3878.png)

src/cascadia/PublicTerminalCore/HwndTerminal.cpp

@@ -16,6 +16,14 @@ using namespace ::Microsoft::Terminal::Core;
 
 static LPCWSTR term_window_class = L"HwndTerminalClass";
 
+static constexpr bool _IsMouseMessage(UINT uMsg)
+{
+    return uMsg == WM_LBUTTONDOWN || uMsg == WM_LBUTTONUP || uMsg == WM_LBUTTONDBLCLK ||
+           uMsg == WM_MBUTTONDOWN || uMsg == WM_MBUTTONUP || uMsg == WM_MBUTTONDBLCLK ||
+           uMsg == WM_RBUTTONDOWN || uMsg == WM_RBUTTONUP || uMsg == WM_RBUTTONDBLCLK ||
+           uMsg == WM_MOUSEMOVE || uMsg == WM_MOUSEWHEEL;
+}
+
 LRESULT CALLBACK HwndTerminal::HwndTerminalWndProc(
     HWND hwnd,
     UINT uMsg,
@@ -27,6 +35,14 @@ LRESULT CALLBACK HwndTerminal::HwndTerminalWndProc(
 
     if (terminal)
     {
+        if (_IsMouseMessage(uMsg) && terminal->_CanSendVTMouseInput())
+        {
+            if (terminal->_SendMouseEvent(uMsg, wParam, lParam))
+            {
+                return 0;
+            }
+        }
+
         switch (uMsg)
         {
         case WM_GETOBJECT:
@@ -509,6 +525,36 @@ static ControlKeyStates getControlKeyState() noexcept
     return flags;
 }
 
+bool HwndTerminal::_CanSendVTMouseInput() const noexcept
+{
+    // Only allow the transit of mouse events if shift isn't pressed.
+    const bool shiftPressed = GetKeyState(VK_SHIFT) < 0;
+    return !shiftPressed && _focused && _terminal->IsTrackingMouseInput();
+}
+
+bool HwndTerminal::_SendMouseEvent(UINT uMsg, WPARAM wParam, LPARAM lParam) noexcept
+try
+{
+    const til::point cursorPosition{
+        GET_X_LPARAM(lParam),
+        GET_Y_LPARAM(lParam),
+    };
+
+    const til::size fontSize{ this->_actualFont.GetSize() };
+    short wheelDelta{ 0 };
+    if (uMsg == WM_MOUSEWHEEL)
+    {
+        wheelDelta = HIWORD(wParam);
+    }
+
+    return _terminal->SendMouseEvent(cursorPosition / fontSize, uMsg, getControlKeyState(), wheelDelta);
+}
+catch (...)
+{
+    LOG_CAUGHT_EXCEPTION();
+    return false;
+}
+
 void _stdcall TerminalSendKeyEvent(void* terminal, WORD vkey, WORD scanCode)
 {
     const auto publicTerminal = static_cast<const HwndTerminal*>(terminal);
@@ -596,6 +642,18 @@ void _stdcall TerminalSetCursorVisible(void* terminal, const bool visible)
     publicTerminal->_terminal->SetCursorOn(visible);
 }
 
+void __stdcall TerminalSetFocus(void* terminal)
+{
+    auto publicTerminal = static_cast<HwndTerminal*>(terminal);
+    publicTerminal->_focused = true;
+}
+
+void __stdcall TerminalKillFocus(void* terminal)
+{
+    auto publicTerminal = static_cast<HwndTerminal*>(terminal);
+    publicTerminal->_focused = false;
+}
+
 // Routine Description:
 // - Copies the text given onto the global system clipboard.
 // Arguments:

src/cascadia/PublicTerminalCore/HwndTerminal.hpp

@@ -38,6 +38,8 @@ __declspec(dllexport) void _stdcall TerminalSendKeyEvent(void* terminal, WORD vk
 __declspec(dllexport) void _stdcall TerminalSendCharEvent(void* terminal, wchar_t ch, WORD scanCode);
 __declspec(dllexport) void _stdcall TerminalBlinkCursor(void* terminal);
 __declspec(dllexport) void _stdcall TerminalSetCursorVisible(void* terminal, const bool visible);
+__declspec(dllexport) void _stdcall TerminalSetFocus(void* terminal);
+__declspec(dllexport) void _stdcall TerminalKillFocus(void* terminal);
 };
 
 struct HwndTerminal : ::Microsoft::Console::Types::IControlAccessibilityInfo
@@ -75,6 +77,8 @@ struct HwndTerminal : ::Microsoft::Console::Types::IControlAccessibilityInfo
     std::unique_ptr<::Microsoft::Console::Render::Renderer> _renderer;
     std::unique_ptr<::Microsoft::Console::Render::DxEngine> _renderEngine;
 
+    bool _focused{ false };
+
     std::chrono::milliseconds _multiClickTime;
     unsigned int _multiClickCounter{};
     std::chrono::steady_clock::time_point _lastMouseClickTimestamp{};
@@ -93,6 +97,8 @@ struct HwndTerminal : ::Microsoft::Console::Types::IControlAccessibilityInfo
     friend void _stdcall TerminalSetTheme(void* terminal, TerminalTheme theme, LPCWSTR fontFamily, short fontSize, int newDpi);
     friend void _stdcall TerminalBlinkCursor(void* terminal);
     friend void _stdcall TerminalSetCursorVisible(void* terminal, const bool visible);
+    friend void _stdcall TerminalSetFocus(void* terminal);
+    friend void _stdcall TerminalKillFocus(void* terminal);
 
     void _UpdateFont(int newDpi);
     void _WriteTextToConnection(const std::wstring& text) noexcept;
@@ -106,6 +112,9 @@ struct HwndTerminal : ::Microsoft::Console::Types::IControlAccessibilityInfo
     HRESULT _MoveSelection(LPARAM lParam) noexcept;
     IRawElementProviderSimple* _GetUiaProvider() noexcept;
 
+    bool _CanSendVTMouseInput() const noexcept;
+    bool _SendMouseEvent(UINT uMsg, WPARAM wParam, LPARAM lParam) noexcept;
+
     // Inherited via IControlAccessibilityInfo
     COORD GetFontSize() const override;
     RECT GetBounds() const noexcept override;

src/cascadia/WpfTerminalControl/NativeMethods.cs

@@ -221,6 +221,12 @@ public enum SetWindowPosFlags : uint
         [DllImport("PublicTerminalCore.dll", CallingConvention = CallingConvention.StdCall)]
         public static extern void TerminalSetCursorVisible(IntPtr terminal, bool visible);
 
+        [DllImport("PublicTerminalCore.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
+        public static extern void TerminalSetFocus(IntPtr terminal);
+
+        [DllImport("PublicTerminalCore.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
+        public static extern void TerminalKillFocus(IntPtr terminal);
+
         [DllImport("user32.dll", SetLastError = true)]
         public static extern IntPtr SetFocus(IntPtr hWnd);
 

src/cascadia/WpfTerminalControl/TerminalContainer.cs

@@ -220,9 +220,11 @@ private IntPtr TerminalContainer_MessageHook(IntPtr hwnd, int msg, IntPtr wParam
                 switch ((NativeMethods.WindowMessage)msg)
                 {
                     case NativeMethods.WindowMessage.WM_SETFOCUS:
+                        NativeMethods.TerminalSetFocus(this.terminal);
                         this.blinkTimer?.Start();
                         break;
                     case NativeMethods.WindowMessage.WM_KILLFOCUS:
+                        NativeMethods.TerminalKillFocus(this.terminal);
                         this.blinkTimer?.Stop();
                         NativeMethods.TerminalSetCursorVisible(this.terminal, false);
                         break;