Imm32 preedit

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -34,7 +34,7 @@ namespace Avalonia.Controls.Presenters
 
         public static readonly StyledProperty<IBrush?> CaretBrushProperty =
             AvaloniaProperty.Register<TextPresenter, IBrush?>(nameof(CaretBrush));
-        
+
         public static readonly DirectProperty<TextPresenter, int> SelectionStartProperty =
             TextBox.SelectionStartProperty.AddOwner<TextPresenter>(
                 o => o.SelectionStart,
@@ -44,7 +44,7 @@ namespace Avalonia.Controls.Presenters
             TextBox.SelectionEndProperty.AddOwner<TextPresenter>(
                 o => o.SelectionEnd,
                 (o, v) => o.SelectionEnd = v);
-        
+
         /// <summary>
         /// Defines the <see cref="Text"/> property.
         /// </summary>
@@ -80,7 +80,7 @@ namespace Avalonia.Controls.Presenters
         /// </summary>
         public static readonly StyledProperty<double> LineHeightProperty =
             TextBlock.LineHeightProperty.AddOwner<TextPresenter>();
-        
+
         /// <summary>
         /// Defines the <see cref="Background"/> property.
         /// </summary>
@@ -114,7 +114,7 @@ namespace Avalonia.Controls.Presenters
         }
 
         public event EventHandler? CaretBoundsChanged;
-        
+
         /// <summary>
         /// Gets or sets a brush used to paint the control's background.
         /// </summary>
@@ -202,7 +202,7 @@ namespace Avalonia.Controls.Presenters
             get => GetValue(TextWrappingProperty);
             set => SetValue(TextWrappingProperty, value);
         }
-        
+
         /// <summary>
         /// Gets or sets the line height. By default, this is set to <see cref="double.NaN"/>, which determines the appropriate height automatically.
         /// </summary>
@@ -232,11 +232,11 @@ namespace Avalonia.Controls.Presenters
                 {
                     return _textLayout;
                 }
-                
+
                 _textLayout = CreateTextLayout();
 
                 UpdateCaret(_lastCharacterHit);
-                
+
                 return _textLayout;
             }
         }
@@ -285,7 +285,7 @@ namespace Avalonia.Controls.Presenters
             get => GetValue(CaretBrushProperty);
             set => SetValue(CaretBrushProperty, value);
         }
-        
+
         public int SelectionStart
         {
             get
@@ -313,7 +313,7 @@ namespace Avalonia.Controls.Presenters
                 SetAndRaise(SelectionEndProperty, ref _selectionEnd, value);
             }
         }
-        
+
         protected override bool BypassFlowDirectionPolicies => true;
 
         /// <summary>
@@ -330,9 +330,9 @@ namespace Avalonia.Controls.Presenters
             var foreground = Foreground;
             var maxWidth = MathUtilities.IsZero(constraint.Width) ? double.PositiveInfinity : constraint.Width;
             var maxHeight = MathUtilities.IsZero(constraint.Height) ? double.PositiveInfinity : constraint.Height;
-            
+
             var textLayout = new TextLayout(text, typeface, FontSize, foreground, TextAlignment,
-                TextWrapping, maxWidth: maxWidth, maxHeight: maxHeight, textStyleOverrides: textStyleOverrides, 
+                TextWrapping, maxWidth: maxWidth, maxHeight: maxHeight, textStyleOverrides: textStyleOverrides,
                 flowDirection: FlowDirection, lineHeight: LineHeight);
 
             return textLayout;
@@ -398,7 +398,7 @@ namespace Avalonia.Controls.Presenters
             {
                 return;
             }
-            
+
             var caretBrush = CaretBrush?.ToImmutable();
 
             if (caretBrush is null)
@@ -423,13 +423,13 @@ namespace Avalonia.Controls.Presenters
 
             context.DrawLine(new ImmutablePen(caretBrush), p1, p2);
         }
-        
+
         private (Point, Point) GetCaretPoints()
         {
             var x = Math.Floor(_caretBounds.X) + 0.5;
             var y = Math.Floor(_caretBounds.Y) + 0.5;
             var b = Math.Ceiling(_caretBounds.Bottom) - 0.5;
-            
+
             var caretIndex = _lastCharacterHit.FirstCharacterIndex + _lastCharacterHit.TrailingLength;
             var lineIndex = TextLayout.GetLineIndexFromCharacterIndex(caretIndex, _lastCharacterHit.TrailingLength > 0);
             var textLine = TextLayout.TextLines[lineIndex];
@@ -438,7 +438,7 @@ namespace Avalonia.Controls.Presenters
             {
                 x -= 1;
             }
-            
+
             return (new Point(x, y), new Point(x, b));
         }
 
@@ -524,17 +524,7 @@ namespace Avalonia.Controls.Presenters
             var start = Math.Min(selectionStart, selectionEnd);
             var length = Math.Max(selectionStart, selectionEnd) - start;
 
-            List<ValueSpan<TextRunProperties>>? textStyleOverrides = null;
-
-            if (length > 0 && SelectionForegroundBrush != null)
-            {
-                textStyleOverrides = new List<ValueSpan<TextRunProperties>>
-                {
-                    new ValueSpan<TextRunProperties>(start, length,
-                        new GenericTextRunProperties(typeface, FontSize,
-                            foregroundBrush: SelectionForegroundBrush))
-                };
-            }
+            IReadOnlyList<ValueSpan<TextRunProperties>>? textStyleOverrides = null;
 
             var foreground = Foreground;
 
@@ -542,20 +532,26 @@ namespace Avalonia.Controls.Presenters
             {
                 var preeditHighlight = new ValueSpan<TextRunProperties>(_caretIndex, _preeditText.Length,
                         new GenericTextRunProperties(typeface, FontSize,
-                        foregroundBrush: foreground,
-                        textDecorations: TextDecorations.Underline));
+                        foregroundBrush: Foreground,
+                        textDecorations: TextDecorations.Underline,
+                        backgroundBrush: SelectionBrush));
 
-                if (textStyleOverrides == null)
+                textStyleOverrides = new[]
+                {
+                    preeditHighlight
+                };
+            }
+            else
+            {
+                if (length > 0 && SelectionForegroundBrush != null)
                 {
-                    textStyleOverrides = new List<ValueSpan<TextRunProperties>>
+                    textStyleOverrides = new[]
                     {
-                        preeditHighlight
+                        new ValueSpan<TextRunProperties>(start, length,
+                        new GenericTextRunProperties(typeface, FontSize,
+                            foregroundBrush: SelectionForegroundBrush))
                     };
                 }
-                else
-                {
-                    textStyleOverrides.Add(preeditHighlight);
-                }
             }
 
             if (PasswordChar != default(char) && !RevealPassword)
@@ -574,7 +570,7 @@ namespace Avalonia.Controls.Presenters
         protected virtual void InvalidateTextLayout()
         {
             _textLayout = null;
-            
+
             InvalidateMeasure();
         }
 
@@ -623,7 +619,7 @@ namespace Avalonia.Controls.Presenters
         private void CaretTimerTick(object? sender, EventArgs e)
         {
             _caretBlink = !_caretBlink;
-            
+
             InvalidateVisual();
         }
 
@@ -633,7 +629,7 @@ namespace Avalonia.Controls.Presenters
             var textLine = TextLayout.TextLines[lineIndex];
 
             var characterHit = textLine.GetPreviousCaretCharacterHit(new CharacterHit(textPosition));
-            
+
             var nextCaretCharacterHit = textLine.GetNextCaretCharacterHit(characterHit);
 
             if (nextCaretCharacterHit.FirstCharacterIndex <= textPosition)
@@ -653,8 +649,8 @@ namespace Avalonia.Controls.Presenters
             _navigationPosition = _caretBounds.Position;
 
             CaretChanged();
-        } 
-        
+        }
+
         public void MoveCaretToPoint(Point point)
         {
             var hit = TextLayout.HitTestPoint(point);
@@ -685,7 +681,7 @@ namespace Avalonia.Controls.Presenters
                 }
 
                 var textLine = TextLayout.TextLines[lineIndex];
-                
+
                 currentY += textLine.Height;
             }
             else
@@ -701,9 +697,9 @@ namespace Avalonia.Controls.Presenters
             }
 
             var navigationPosition = _navigationPosition;
-            
+
             MoveCaretToPoint(new Point(currentX, currentY));
-            
+
             _navigationPosition = navigationPosition.WithY(_caretBounds.Y);
 
             CaretChanged();
@@ -714,11 +710,11 @@ namespace Avalonia.Controls.Presenters
             if (Text is null)
             {
                 return default;
-            }          
+            }
 
             var characterHit = _lastCharacterHit;
             var caretIndex = characterHit.FirstCharacterIndex + characterHit.TrailingLength;
-            
+
             var lineIndex = TextLayout.GetLineIndexFromCharacterIndex(caretIndex, false);
 
             if (lineIndex < 0)
@@ -740,11 +736,11 @@ namespace Avalonia.Controls.Presenters
                     {
                         characterHit = new CharacterHit(caretIndex);
                     }
-                    
+
                     if (caretIndex >= Text.Length)
                     {
                         characterHit = new CharacterHit(Text.Length);
-                        
+
                         break;
                     }
 
@@ -756,10 +752,10 @@ namespace Avalonia.Controls.Presenters
                     if (caretIndex <= CaretIndex)
                     {
                         lineIndex++;
-                        
+
                         continue;
                     }
-                    
+
                     break;
                 }
             }
@@ -786,7 +782,7 @@ namespace Avalonia.Controls.Presenters
 
             return characterHit;
         }
-        
+
         public void MoveCaretHorizontal(LogicalDirection direction = LogicalDirection.Forward)
         {
             if (FlowDirection == FlowDirection.RightToLeft)
@@ -808,9 +804,9 @@ namespace Avalonia.Controls.Presenters
         private void UpdateCaret(CharacterHit characterHit)
         {
             _lastCharacterHit = characterHit;
-            
+
             var caretIndex = characterHit.FirstCharacterIndex + characterHit.TrailingLength;
-            
+
             var lineIndex = TextLayout.GetLineIndexFromCharacterIndex(caretIndex, characterHit.TrailingLength > 0);
             var textLine = TextLayout.TextLines[lineIndex];
             var distanceX = textLine.GetDistanceFromCharacterHit(characterHit);
@@ -825,7 +821,7 @@ namespace Avalonia.Controls.Presenters
             }
 
             var caretBounds = new Rect(distanceX, distanceY, 0, textLine.Height);
-            
+
             if (caretBounds != _caretBounds)
             {
                 _caretBounds = caretBounds;
@@ -846,40 +842,40 @@ namespace Avalonia.Controls.Presenters
             base.OnDetachedFromVisualTree(e);
 
             _caretTimer.Stop();
-            
+
             _caretTimer.Tick -= CaretTimerTick;
         }
 
         protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
-            
+
             switch (change.Property.Name)
             {
-                case nameof (Foreground):
-                case nameof (FontSize):
-                case nameof (FontStyle):
-                case nameof (FontWeight):
-                case nameof (FontFamily):
-                case nameof (FontStretch):
+                case nameof(Foreground):
+                case nameof(FontSize):
+                case nameof(FontStyle):
+                case nameof(FontWeight):
+                case nameof(FontFamily):
+                case nameof(FontStretch):
 
-                case nameof (Text):
-                case nameof (PreeditText):
-                case nameof (TextAlignment):
-                case nameof (TextWrapping):
+                case nameof(Text):
+                case nameof(PreeditText):
+                case nameof(TextAlignment):
+                case nameof(TextWrapping):
 
-                case nameof (SelectionStart):
-                case nameof (SelectionEnd):
-                case nameof (SelectionForegroundBrush):
+                case nameof(SelectionStart):
+                case nameof(SelectionEnd):
+                case nameof(SelectionForegroundBrush):
 
-                case nameof (PasswordChar):
-                case nameof (RevealPassword):
+                case nameof(PasswordChar):
+                case nameof(RevealPassword):
 
                 case nameof(FlowDirection):
-                {
-                    InvalidateTextLayout();
-                    break;
-                }
+                    {
+                        InvalidateTextLayout();
+                        break;
+                    }
             }
         }
     }

src/Avalonia.Controls/TextBox.cs

@@ -1142,7 +1142,7 @@ namespace Avalonia.Controls
 
         protected override void OnPointerPressed(PointerPressedEventArgs e)
         {
-            if (_presenter == null)
+            if (_presenter == null || !string.IsNullOrEmpty(_presenter.PreeditText))
             {
                 return;
             }

src/Windows/Avalonia.Win32/Input/Imm32CaretManager.cs

@@ -7,14 +7,11 @@ namespace Avalonia.Win32.Input
     {
         private bool _isCaretCreated;
 
-        public void TryCreate(int _langId, IntPtr hwnd)
+        public void TryCreate(IntPtr hwnd)
         {
             if (!_isCaretCreated)
             {
-                if (_langId == LANG_ZH || _langId == LANG_JA)
-                {
-                    _isCaretCreated = CreateCaret(hwnd, IntPtr.Zero, 2, 10);
-                }
+                _isCaretCreated = CreateCaret(hwnd, IntPtr.Zero, 2, 2);               
             }
         }
 
@@ -31,6 +28,7 @@ namespace Avalonia.Win32.Input
             if (_isCaretCreated)
             {
                 DestroyCaret();
+
                 _isCaretCreated = false;
             }
         }

src/Windows/Avalonia.Win32/Input/Imm32InputMethod.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Runtime.InteropServices;
+using System.Text;
 using Avalonia.Input.TextInput;
 using Avalonia.Threading;
 
@@ -12,102 +14,125 @@ namespace Avalonia.Win32.Input
     class Imm32InputMethod : ITextInputMethodImpl
     {
         public IntPtr HWND { get; private set; }
-        private IntPtr _defaultImc;
+        private IntPtr _currentHimc;
         private WindowImpl _parent;
-        private bool _active;
-        private bool _showCompositionWindow;
+        private ITextInputMethodClient _client;
+
         private Imm32CaretManager _caretManager = new();
-        private bool _showCandidateList;
+
         private ushort _langId;
         private const int _caretMargin = 1;
-        
-        public void SetLanguageAndWindow(WindowImpl parent, IntPtr hwnd, IntPtr HKL)
+
+        public bool IsActive => _client != null;
+
+        public bool IsComposing { get; set; }
+
+        public bool ShowCompositionWindow => false;
+
+        public void CreateCaret()
+        {
+            _caretManager.TryCreate(HWND);
+        }
+
+        public void EnableImm()
         {
-            if (HWND != hwnd)
+            var himc = ImmGetContext(HWND);
+
+            if(himc == IntPtr.Zero)
+            {
+                himc = ImmCreateContext();
+            }
+
+            if(himc != _currentHimc)
             {
-                _defaultImc = IntPtr.Zero;
+                if(_currentHimc != IntPtr.Zero)
+                {
+                    DisableImm();
+                }
+
+                ImmAssociateContext(HWND, himc);
+
+                ImmReleaseContext(HWND, himc);
+
+                _currentHimc = himc;
+
+                _caretManager.TryCreate(HWND);
             }
+        }
+
+        public void DisableImm()
+        {
+            _caretManager.TryDestroy();
+
+            Reset();
+
+            ImmAssociateContext(HWND, IntPtr.Zero);
+
+            _caretManager.TryDestroy();
+
+            _currentHimc = IntPtr.Zero;
+        }
+
+        public void SetLanguageAndWindow(WindowImpl parent, IntPtr hwnd, IntPtr HKL)
+        {
             HWND = hwnd;
+
             _parent = parent;
-            _active = false;
-            _langId = PRIMARYLANGID(LGID(HKL));
-            _showCompositionWindow = true;
-            _showCandidateList = true;
 
-            IsComposing = false;
+            var langId= PRIMARYLANGID(LGID(HKL));
+
+            if(langId != _langId)
+            {
+                DisableImm();
+            }
+
+            _langId = langId;
+
+            EnableImm();
         }
 
         public void ClearLanguageAndWindow()
         {
-            if (HWND != IntPtr.Zero && _defaultImc != IntPtr.Zero)
-            {
-                ImmReleaseContext(HWND, _defaultImc);
-            }
+            DisableImm();
 
-            _defaultImc = IntPtr.Zero;
             HWND = IntPtr.Zero;
             _parent = null;
-            _active = false;
+            _client = null;
             _langId = 0;
-            _showCompositionWindow = false;
-            _showCandidateList = false;
 
             IsComposing = false;
         }
 
         //Dependant on CurrentThread. When Avalonia will support Multiple Dispatchers -
         //every Dispatcher should have their own InputMethod.
-        public static Imm32InputMethod Current { get; } = new Imm32InputMethod();
+        public static Imm32InputMethod Current { get; } = new Imm32InputMethod();    
 
-        private IntPtr DefaultImc
+        public void Reset()
         {
-            get
+            Dispatcher.UIThread.Post(() =>
             {
-                if (_defaultImc == IntPtr.Zero &&
-                    HWND != IntPtr.Zero)
-                {
-                    _defaultImc = ImmGetContext(HWND);
-                    ImmReleaseContext(HWND, _defaultImc);
-                }
+                var himc = ImmGetContext(HWND);
 
-                if (_defaultImc == IntPtr.Zero)
+                if (IsComposing)
                 {
-                    _defaultImc = ImmCreateContext();
+                    ImmNotifyIME(himc, NI_COMPOSITIONSTR, CPS_COMPLETE, 0);
+                   
+                    IsComposing = false;
                 }
 
-                return _defaultImc;
-            }
-        }
-
-        public void Reset()
-        {
-            if (IsComposing)
-            {
-                Dispatcher.UIThread.Post(() =>
-                {
-                    ImmNotifyIME(DefaultImc, NI_COMPOSITIONSTR, CPS_COMPLETE, 0);
-                    ImmReleaseContext(HWND, DefaultImc);
-                    IsComposing = false;
-                });
-            }
+                ImmReleaseContext(HWND, himc);
+            });
         }
 
         public void SetClient(ITextInputMethodClient client)
         {
-            _active = client is { };
+            _client = client;
+
             Dispatcher.UIThread.Post(() =>
             {
-                if (_active)
+                if (IsActive)
                 {
-                    if (DefaultImc != IntPtr.Zero)
-                    {
-                        _caretManager.TryCreate(_langId, HWND);
-                        // Load the default IME context.
-                        // NOTE(hbono)
-                        //   IMM ignores this call if the IME context is loaded. Therefore, we do
-                        //   not have to check whether or not the IME context is loaded.
-                        ImmAssociateContext(HWND, _defaultImc);
-                    }
+                    EnableImm();
                 }
                 else
                 {
@@ -116,14 +141,8 @@ namespace Avalonia.Win32.Input
                     // mouse button and selected a password input while composing a text.
                     // For this case, we have to complete the ongoing composition and
                     // clean up the resources attached to this object BEFORE DISABLING THE IME.
-                    if (IsComposing)
-                    {
-                        ImmNotifyIME(DefaultImc, NI_COMPOSITIONSTR, CPS_COMPLETE, 0);
-                        ImmReleaseContext(HWND, DefaultImc);
-                        IsComposing = false;
-                    }
-                    ImmAssociateContext(HWND, IntPtr.Zero);
-                    _caretManager.TryDestroy();
+
+                    DisableImm();
                 }
             });
         }
@@ -131,19 +150,23 @@ namespace Avalonia.Win32.Input
         public void SetCursorRect(Rect rect)
         {
             var focused = GetActiveWindow() == HWND;
+
             if (!focused)
             {
                 return;
             }
+
             Dispatcher.UIThread.Post(() =>
             {
-                IntPtr himc = DefaultImc;
+                var himc = ImmGetContext(HWND);
+
                 if (himc == IntPtr.Zero)
                 {
                     return;
                 }
 
                 MoveImeWindow(rect, himc);
+
                 ImmReleaseContext(HWND, himc);
             });
         }
@@ -157,8 +180,7 @@ namespace Avalonia.Win32.Input
             var s = _parent?.DesktopScaling ?? 1;
             var (x1, y1, x2, y2) = ((int) (p1.X * s), (int) (p1.Y * s), (int) (p2.X * s), (int) (p2.Y * s));
 
-            if (!_showCompositionWindow &&
-                _langId == LANG_ZH)
+            if (!ShowCompositionWindow && _langId == LANG_ZH)
             {
                 // Chinese IMEs ignore function calls to ::ImmSetCandidateWindow()
                 // when a user disables TSF (Text Service Framework) and CUAS (Cicero
@@ -175,12 +197,13 @@ namespace Avalonia.Win32.Input
                     dwStyle = CFS_CANDIDATEPOS,
                     ptCurrentPos = new POINT {X = x2, Y = y2}
                 };
+
                 ImmSetCandidateWindow(himc, ref candidateForm);
             }
-            
+
             _caretManager.TryMove(x2, y2);
 
-            if (_showCompositionWindow)
+            if (ShowCompositionWindow)
             {
                 ConfigureCompositionWindow(x1, y1, himc, y2 - y1);
                 // Don't need to set the position of candidate window.
@@ -214,6 +237,7 @@ namespace Avalonia.Win32.Input
                 ptCurrentPos = new POINT {X = x1, Y = y1},
                 rcArea = new RECT {left = x1, top = y1, right = x2, bottom = y2 + _caretMargin}
             };
+
             ImmSetCandidateWindow(himc, ref excludeRectangle);
         }
 
@@ -224,6 +248,7 @@ namespace Avalonia.Win32.Input
                 dwStyle = CFS_POINT,
                 ptCurrentPos = new POINT {X = x1, Y = y1},
             };
+
             ImmSetCompositionWindow(himc, ref compForm);
 
             var logFont = new LOGFONT()
@@ -231,6 +256,7 @@ namespace Avalonia.Win32.Input
                 lfHeight = height,
                 lfQuality = 5 //CLEARTYPE_QUALITY
             };
+
             ImmSetCompositionFont(himc, ref logFont);
         }
         
@@ -238,8 +264,43 @@ namespace Avalonia.Win32.Input
         {
             // we're skipping this. not usable on windows
         }
+
+        public void CompositionChanged()
+        {
+            if (!IsComposing)
+            {
+                return;
+            }
+
+            if(!IsActive || !_client.SupportsPreedit)
+            {
+                return;
+            }
+
+            var composition = GetCompositionString();
+
+            _client.SetPreeditText(composition);
+        }
         
-        public bool IsComposing { get; set; }
+        private string GetCompositionString()
+        {
+            var himc = ImmGetContext(HWND);
+
+            var length = ImmGetCompositionString(himc, GCS.GCS_COMPSTR, IntPtr.Zero, 0);
+
+            var buffer = new byte[length];
+
+            unsafe
+            {
+                fixed (byte* bufferPtr = buffer)
+                {
+                    var error = ImmGetCompositionString(himc, GCS.GCS_COMPSTR, (IntPtr)bufferPtr, (uint)length);
+
+                    return Encoding.Unicode.GetString(buffer, 0, buffer.Length);
+                }
+            }
+          
+        }
 
         ~Imm32InputMethod()
         {

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1766,6 +1766,46 @@ namespace Avalonia.Win32.Interop
         [DllImport("user32.dll")]
         internal static extern int SetWindowCompositionAttribute(IntPtr hwnd, ref WindowCompositionAttributeData data);
 
+        [Flags]
+        public enum GCS : uint
+        {
+            /// <summary>Retrieve or update the attribute of the composition string.</summary>
+            GCS_COMPATTR = 0x0010,
+
+            /// <summary>Retrieve or update clause information of the composition string.</summary>
+            GCS_COMPCLAUSE = 0x0020,
+
+            /// <summary>Retrieve or update the attributes of the reading string of the current composition.</summary>
+            GCS_COMPREADATTR = 0x0002,
+
+            /// <summary>Retrieve or update the clause information of the reading string of the composition string.</summary>
+            GCS_COMPREADCLAUSE = 0x0004,
+
+            /// <summary>Retrieve or update the reading string of the current composition.</summary>
+            GCS_COMPREADSTR = 0x0001,
+
+            /// <summary>Retrieve or update the current composition string.</summary>
+            GCS_COMPSTR = 0x0008,
+
+            /// <summary>Retrieve or update the cursor position in composition string.</summary>
+            GCS_CURSORPOS = 0x0080,
+
+            /// <summary>Retrieve or update the starting position of any changes in composition string.</summary>
+            GCS_DELTASTART = 0x0100,
+
+            /// <summary>Retrieve or update clause information of the result string.</summary>
+            GCS_RESULTCLAUSE = 0x1000,
+
+            /// <summary>Retrieve or update clause information of the reading string.</summary>
+            GCS_RESULTREADCLAUSE = 0x0400,
+
+            /// <summary>Retrieve or update the reading string.</summary>
+            GCS_RESULTREADSTR = 0x0200,
+
+            /// <summary>Retrieve or update the string of the composition result.</summary>
+            GCS_RESULTSTR = 0x0800,
+        }
+
         [DllImport("imm32.dll", SetLastError = true)]
         public static extern IntPtr ImmGetContext(IntPtr hWnd);
         [DllImport("imm32.dll", SetLastError = true)]
@@ -1788,6 +1828,29 @@ namespace Avalonia.Win32.Interop
         public static extern bool ImmSetCompositionWindow(IntPtr hIMC, ref COMPOSITIONFORM lpComp);
         [DllImport("imm32.dll")]
         public static extern bool ImmSetCompositionFont(IntPtr hIMC, ref LOGFONT lf);
+
+        [DllImport("imm32.dll", SetLastError = false, CharSet = CharSet.Unicode)]
+        public static extern int ImmGetCompositionString(IntPtr hIMC, GCS dwIndex, [Out, Optional] IntPtr lpBuf, uint dwBufLen);
+
+        public static string ImmGetCompositionString(IntPtr hIMC, GCS dwIndex)
+        {
+            int bufferLength = ImmGetCompositionString(hIMC, dwIndex, IntPtr.Zero, 0);
+
+            if (bufferLength > 0)
+            {
+                var buffer = new byte[bufferLength];
+
+                fixed(byte* bufferPtr = buffer)
+                {
+                    var error = ImmGetCompositionString(hIMC, dwIndex, (IntPtr)bufferPtr, (uint)bufferLength);
+
+                    return Marshal.PtrToStringUni((IntPtr)bufferPtr);
+                }           
+            }
+
+            return null;
+        }
+
         [DllImport("imm32.dll")]
         public static extern bool ImmNotifyIME(IntPtr hIMC, int dwAction, int dwIndex, int dwValue);
         [DllImport("user32.dll")]
@@ -1827,7 +1890,13 @@ namespace Avalonia.Win32.Interop
         public const int CFS_EXCLUDE = 0x0080;
         public const int CFS_POINT = 0x0002;
         public const int CFS_RECT = 0x0001;
-        public const uint ISC_SHOWUICOMPOSITIONWINDOW = 0x80000000;
+
+        // lParam for WM_IME_SETCONTEXT
+        public const long ISC_SHOWUICANDIDATEWINDOW = 0x00000001;
+        public const long ISC_SHOWUICOMPOSITIONWINDOW = 0x80000000;
+        public const long ISC_SHOWUIGUIDELINE = 0x40000000;
+        public const long ISC_SHOWUIALLCANDIDATEWINDOW = 0x0000000F;
+        public const long ISC_SHOWUIALL = 0xC000000F;
 
         public const int NI_COMPOSITIONSTR = 21;
         public const int CPS_COMPLETE = 1;

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -527,22 +527,22 @@ namespace Avalonia.Win32
                     }
 
                 case WindowsMessage.WM_PAINT:
-                {
-                    using(NonPumpingSyncContext.Use())
-                    using (_rendererLock.Lock())
                     {
-                        if (BeginPaint(_hwnd, out PAINTSTRUCT ps) != IntPtr.Zero)
+                        using (NonPumpingSyncContext.Use())
+                        using (_rendererLock.Lock())
                         {
-                            var f = RenderScaling;
-                            var r = ps.rcPaint;
-                            Paint?.Invoke(new Rect(r.left / f, r.top / f, (r.right - r.left) / f,
-                                (r.bottom - r.top) / f));
-                            EndPaint(_hwnd, ref ps);
+                            if (BeginPaint(_hwnd, out PAINTSTRUCT ps) != IntPtr.Zero)
+                            {
+                                var f = RenderScaling;
+                                var r = ps.rcPaint;
+                                Paint?.Invoke(new Rect(r.left / f, r.top / f, (r.right - r.left) / f,
+                                    (r.bottom - r.top) / f));
+                                EndPaint(_hwnd, ref ps);
+                            }
                         }
-                    }
 
-                    return IntPtr.Zero;
-                }
+                        return IntPtr.Zero;
+                    }
 
 
                 case WindowsMessage.WM_ENTERSIZEMOVE:
@@ -551,7 +551,7 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_SIZE:
                     {
-                        using(NonPumpingSyncContext.Use())
+                        using (NonPumpingSyncContext.Use())
                         using (_rendererLock.Lock())
                         {
                             // Do nothing here, just block until the pending frame render is completed on the render thread
@@ -651,13 +651,19 @@ namespace Avalonia.Win32
                     }
                 case WindowsMessage.WM_IME_SETCONTEXT:
                     {
-                        // TODO if we implement preedit, disable the composition window:
-                        // lParam = new IntPtr((int)(((uint)lParam.ToInt64()) & ~ISC_SHOWUICOMPOSITIONWINDOW));
+                        DefWindowProc(Hwnd, msg, wParam, (IntPtr)(lParam.ToInt64() & ~ISC_SHOWUICOMPOSITIONWINDOW));
+
                         UpdateInputMethod(GetKeyboardLayout(0));
+
+                        return IntPtr.Zero;
+                    }
+                case WindowsMessage.WM_IME_COMPOSITION:
+                    {
+                        Imm32InputMethod.Current.CompositionChanged();
+
                         break;
                     }
                 case WindowsMessage.WM_IME_CHAR:
-                case WindowsMessage.WM_IME_COMPOSITION:
                 case WindowsMessage.WM_IME_COMPOSITIONFULL:
                 case WindowsMessage.WM_IME_CONTROL:
                 case WindowsMessage.WM_IME_KEYDOWN:
@@ -667,6 +673,7 @@ namespace Avalonia.Win32
                     break;
                 case WindowsMessage.WM_IME_STARTCOMPOSITION:
                     Imm32InputMethod.Current.IsComposing = true;
+                    return IntPtr.Zero;
                     break;
                 case WindowsMessage.WM_IME_ENDCOMPOSITION:
                     Imm32InputMethod.Current.IsComposing = false;
@@ -687,7 +694,7 @@ namespace Avalonia.Win32
                 return UnmanagedMethods.DefWindowProc(hWnd, msg, wParam, lParam);
 #endif
 
-            if(shouldTakeFocus)
+            if (shouldTakeFocus)
             {
                 SetFocus(_hwnd);
             }
@@ -916,14 +923,15 @@ namespace Avalonia.Win32
         {
             // note: for non-ime language, also create it so that emoji panel tracks cursor
             var langid = LGID(hkl);
+
             if (langid == _langid && Imm32InputMethod.Current.HWND == Hwnd)
             {
                 return;
             }
+
             _langid = langid;
 
             Imm32InputMethod.Current.SetLanguageAndWindow(this, Hwnd, hkl);
-
         }
 
         private static int ToInt32(IntPtr ptr)