Fix multitouch and add historical points support

src/Web/Avalonia.Web/Avalonia.Web.csproj

@@ -7,6 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <SupportedPlatform Remove="@(SupportedPlatform)" />
     <SupportedPlatform Include="browser" />
   </ItemGroup>
 

src/Web/Avalonia.Web/AvaloniaView.cs

@@ -1,5 +1,9 @@
 using System;
+using System.Collections.Generic;
+using System.Reflection;
 using System.Runtime.InteropServices.JavaScript;
+
+using Avalonia.Collections.Pooled;
 using Avalonia.Controls;
 using Avalonia.Controls.Embedding;
 using Avalonia.Controls.Platform;
@@ -18,6 +22,7 @@ namespace Avalonia.Web
     [System.Runtime.Versioning.SupportedOSPlatform("browser")] // gets rid of callsite warnings
     public partial class AvaloniaView : ITextInputMethodImpl
     {
+        private static readonly PooledList<RawPointerPoint> s_intermediatePointsPooledList = new(ClearMode.Never);
         private readonly BrowserTopLevelImpl _topLevelImpl;
         private EmbeddableControlRoot _topLevel;
 
@@ -162,94 +167,84 @@ namespace Avalonia.Web
         private bool OnPointerMove(JSObject args)
         {
             var pointerType = args.GetPropertyAsString("pointerType");
+            var point = ExtractRawPointerFromJSArgs(args);
+            var type = pointerType switch
+            {
+                "touch" => RawPointerEventType.TouchUpdate,
+                _ => RawPointerEventType.Move
+            };
 
-            if (pointerType == "touch")
+            var coalescedEvents = new Lazy<IReadOnlyList<RawPointerPoint>?>(() =>
             {
-                var x = args.GetPropertyAsDouble("clientX");
-                var y = args.GetPropertyAsDouble("clientY");
-                long identifier = args.GetPropertyAsInt32("identifier");
+                var points = InputHelper.GetCoalescedEvents(args);
+                s_intermediatePointsPooledList.Clear();
+                s_intermediatePointsPooledList.Capacity = points.Length - 1;
 
-                return _topLevelImpl.RawTouchEvent(RawPointerEventType.TouchUpdate, new Point(x, y),
-                    GetModifiers(args), identifier);
-            }
+                // Skip the last one, as it is already processed point.
+                for (var i = 0; i < points.Length - 1; i++)
+                {
+                    var point = points[i];
+                    s_intermediatePointsPooledList.Add(ExtractRawPointerFromJSArgs(point));
+                }
 
-            var point = ExtractRawPointerFromJSArgs(args);
-            
-            return _topLevelImpl.RawPointerEvent(RawPointerEventType.Move, pointerType!, point, GetModifiers(args), args.GetPropertyAsInt32("pointerId"));
+                return s_intermediatePointsPooledList;
+            });
+
+            return _topLevelImpl.RawPointerEvent(type, pointerType!, point, GetModifiers(args), args.GetPropertyAsInt32("pointerId"), coalescedEvents);
         }
 
         private bool OnPointerDown(JSObject args)
         {
-            var pointerType = args.GetPropertyAsString("pointerType");
-
-            if (pointerType == "touch")
-            {
-                var x = args.GetPropertyAsDouble("clientX");
-                var y = args.GetPropertyAsDouble("clientY");
-                long identifier = args.GetPropertyAsInt32("identifier");
-            
-                return _topLevelImpl.RawTouchEvent(RawPointerEventType.TouchBegin, new Point(x, y),
-                    GetModifiers(args), identifier);
-            }
-
-            var type = args.GetPropertyAsInt32("button") switch
+            var pointerType = args.GetPropertyAsString("pointerType") ?? "mouse";
+            var type = pointerType switch
             {
-                0 => RawPointerEventType.LeftButtonDown,
-                1 => RawPointerEventType.MiddleButtonDown,
-                2 => RawPointerEventType.RightButtonDown,
-                3 => RawPointerEventType.XButton1Down,
-                4 => RawPointerEventType.XButton2Down,
-                // 5 => Pen eraser button,
-                _ => RawPointerEventType.Move
+                "touch" => RawPointerEventType.TouchBegin,
+                _ => args.GetPropertyAsInt32("button") switch
+                {
+                    0 => RawPointerEventType.LeftButtonDown,
+                    1 => RawPointerEventType.MiddleButtonDown,
+                    2 => RawPointerEventType.RightButtonDown,
+                    3 => RawPointerEventType.XButton1Down,
+                    4 => RawPointerEventType.XButton2Down,
+                    5 => RawPointerEventType.XButton1Down, // should be pen eraser button,
+                    _ => RawPointerEventType.Move
+                }
             };
 
             var point = ExtractRawPointerFromJSArgs(args);
-
-            return _topLevelImpl.RawPointerEvent(type, pointerType!, point, GetModifiers(args), args.GetPropertyAsInt32("pointerId"));
+            return _topLevelImpl.RawPointerEvent(type, pointerType, point, GetModifiers(args), args.GetPropertyAsInt32("pointerId"));
         }
 
         private bool OnPointerUp(JSObject args)
         {
             var pointerType = args.GetPropertyAsString("pointerType") ?? "mouse";
-
-            if (pointerType == "touch")
+            var type = pointerType switch
             {
-                var x = args.GetPropertyAsDouble("clientX");
-                var y = args.GetPropertyAsDouble("clientY");
-                long identifier = args.GetPropertyAsInt32("identifier");
-            
-                return _topLevelImpl.RawTouchEvent(RawPointerEventType.TouchEnd, new Point(x, y),
-                    GetModifiers(args), identifier);
-            }
-
-            var type = args.GetPropertyAsInt32("button") switch
-            {
-                0 => RawPointerEventType.LeftButtonUp,
-                1 => RawPointerEventType.MiddleButtonUp,
-                2 => RawPointerEventType.RightButtonUp,
-                3 => RawPointerEventType.XButton1Up,
-                4 => RawPointerEventType.XButton2Up,
-                // 5 => Pen eraser button,
-                _ => RawPointerEventType.Move
+                "touch" => RawPointerEventType.TouchEnd,
+                _ => args.GetPropertyAsInt32("button") switch
+                {
+                    0 => RawPointerEventType.LeftButtonUp,
+                    1 => RawPointerEventType.MiddleButtonUp,
+                    2 => RawPointerEventType.RightButtonUp,
+                    3 => RawPointerEventType.XButton1Up,
+                    4 => RawPointerEventType.XButton2Up,
+                    5 => RawPointerEventType.XButton1Up, // should be pen eraser button,
+                    _ => RawPointerEventType.Move
+                }
             };
 
             var point = ExtractRawPointerFromJSArgs(args);
-
             return _topLevelImpl.RawPointerEvent(type, pointerType, point, GetModifiers(args), args.GetPropertyAsInt32("pointerId"));
         }
         
         private bool OnPointerCancel(JSObject args)
         {
             var pointerType = args.GetPropertyAsString("pointerType") ?? "mouse";
-
             if (pointerType == "touch")
             {
-                var x = args.GetPropertyAsDouble("clientX");
-                var y = args.GetPropertyAsDouble("clientY");
-                long identifier = args.GetPropertyAsInt32("identifier");
-
-                return _topLevelImpl.RawTouchEvent(RawPointerEventType.TouchCancel, new Point(x, y),
-                    GetModifiers(args), identifier);
+                var point = ExtractRawPointerFromJSArgs(args);
+                _topLevelImpl.RawPointerEvent(RawPointerEventType.TouchCancel, pointerType, point,
+                    GetModifiers(args), args.GetPropertyAsInt32("pointerId"));
             }
 
             return false;

src/Web/Avalonia.Web/BrowserTopLevelImpl.cs

@@ -64,35 +64,25 @@ namespace Avalonia.Web
                 Resized?.Invoke(newSize, PlatformResizeReason.User);
             }
         }
-        
-        public bool RawTouchEvent(RawPointerEventType type, Point p, RawInputModifiers modifiers, long touchPointId)
-        {
-            if (_inputRoot is { } && Input is { } input)
-            {
-                var args = new RawTouchEventArgs(_touchDevice, Timestamp, _inputRoot, type, p, modifiers,
-                    touchPointId);
-                
-                input.Invoke(args);
-
-                return args.Handled;
-            }
-
-            return false;
-        }
 
         public bool RawPointerEvent(
             RawPointerEventType eventType, string pointerType,
-            RawPointerPoint p, RawInputModifiers modifiers, long touchPointId)
+            RawPointerPoint p, RawInputModifiers modifiers, long touchPointId,
+            Lazy<IReadOnlyList<RawPointerPoint>?>? intermediatePoints = null)
         {
             if (_inputRoot is { }
                 && Input is { } input)
             {
                 var device = GetPointerDevice(pointerType);
                 var args = device is TouchDevice ?
-                    new RawTouchEventArgs(device, Timestamp, _inputRoot, eventType, p, modifiers, touchPointId) :
+                    new RawTouchEventArgs(device, Timestamp, _inputRoot, eventType, p, modifiers, touchPointId)
+                    {
+                        IntermediatePoints = intermediatePoints
+                    } :
                     new RawPointerEventArgs(device, Timestamp, _inputRoot, eventType, p, modifiers)
                     {
-                        RawPointerId = touchPointId
+                        RawPointerId = touchPointId,
+                        IntermediatePoints = intermediatePoints
                     };
 
                 input.Invoke(args);

src/Web/Avalonia.Web/Interop/InputHelper.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.JavaScript;
 using System.Threading.Tasks;
 
@@ -47,6 +48,9 @@ internal static partial class InputHelper
         [JSMarshalAs<JSType.Function<JSType.String, JSType.Boolean>>]
         Func<string, bool> input);
 
+    [JSImport("InputHelper.getCoalescedEvents", AvaloniaModule.MainModuleName)]
+    [return: JSMarshalAs<JSType.Array<JSType.Object>>]
+    public static partial JSObject[] GetCoalescedEvents(JSObject pointerEvent);
 
     [JSImport("InputHelper.clearInput", AvaloniaModule.MainModuleName)]
     public static partial void ClearInputElement(JSObject htmlElement);

src/Web/Avalonia.Web/webapp/modules/avalonia/input.ts

@@ -154,6 +154,10 @@ export class InputHelper {
         };
     }
 
+    public static getCoalescedEvents(pointerEvent: PointerEvent): PointerEvent[] {
+        return pointerEvent.getCoalescedEvents();
+    }
+
     public static clearInput(inputElement: HTMLInputElement) {
         inputElement.value = "";
     }