Merge pull request #235 from timunie/fix/SnowFlakesControl_RemoveCustomHitTest

Don't use `ICustomHitTest`

Author: maxkatz6

src/Avalonia.Samples/CustomControls/SnowflakesControlSample/Controls/SnowflakesControl.cs

@@ -6,8 +6,8 @@
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Data;
+using Avalonia.Input;
 using Avalonia.Media;
-using Avalonia.Rendering;
 using Avalonia.Threading;
 using SnowflakesControlSample.Models;
 
@@ -17,18 +17,18 @@ namespace SnowflakesControlSample.Controls;
 /// A control to render some <see cref="Snowflake">Snowflakes</see>. This control also adds the needed interaction logic
 /// for the game to operate.
 /// </summary>
-public class SnowflakesControl : Control, ICustomHitTest
+public class SnowflakesControl : Control
 {
     static SnowflakesControl()
     {
         // Make sure Render is updated whenever one of these properties changes
         AffectsRender<SnowflakesControl>(IsRunningProperty, SnowflakesProperty, ScoreProperty);
     }
-    
+
     // We use a stopwatch to measure elapsed time between two render loops as it has higher precision compared to 
     // other options. See: https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.stopwatch
     private readonly Stopwatch _stopwatch = new();
-    
+
     // A collection which holds all current visible score infos to render.
     private readonly ICollection<ScoreHint> _scoreHintsCollection = new Collection<ScoreHint>();
 
@@ -58,7 +58,7 @@ static SnowflakesControl()
         AvaloniaProperty.Register<SnowflakesControl, bool>(nameof(IsRunning));
 
     private IList<Snowflake> _snowflakes = [];
-    
+
     /// <summary>
     /// Gets or sets a List of  <see cref="Snowflake">Snowflakes</see> to render.
     /// </summary>
@@ -69,7 +69,7 @@ public IList<Snowflake> Snowflakes
     }
 
     private int _score;
-    
+
     /// <summary>
     /// Gets or sets the current user score.
     /// </summary>
@@ -78,7 +78,7 @@ public int Score
         get => _score;
         set => SetAndRaise(ScoreProperty, ref _score, value);
     }
-    
+
     /// <summary>
     /// Gets or sets a bool indicating if the Game whether the game is currently running.
     /// </summary>
@@ -87,7 +87,7 @@ public bool IsRunning
         get { return GetValue(IsRunningProperty); }
         set { SetValue(IsRunningProperty, value); }
     }
-    
+
     /// <inheritdoc />
     protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
     {
@@ -100,7 +100,7 @@ protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs chang
             {
                 // Resets and starts the stopwatch
                 _stopwatch.Restart();
-                
+
                 // Clear any previous score hints
                 _scoreHintsCollection.Clear();
             }
@@ -136,7 +136,7 @@ public override void Render(DrawingContext context)
 
         // Bonus 1: Use a custom renderer using Skia-API to display the total score
         context.Custom(new ScoreRenderer(Bounds, $"Your score: {Score:N0}"));
-        
+
         // Bonus 2: Render the score hint if any available.
         foreach (var scoreHint in _scoreHintsCollection.ToArray())
         {
@@ -145,7 +145,7 @@ public override void Render(DrawingContext context)
             {
                 scoreHint.Update(elapsedMilliseconds);
             }
-            
+
             // Use a formatted text to render the score hint.
             var formattedText =
                 new FormattedText(
@@ -155,42 +155,60 @@ public override void Render(DrawingContext context)
                     Typeface.Default,
                     20,
                     new SolidColorBrush(Colors.Yellow, scoreHint.Opacity));
-            
-            context.DrawText(formattedText, scoreHint.GetTopLeftForViewport(Bounds, new Size(formattedText.Width, formattedText.Height)));
+
+            context.DrawText(formattedText,
+                scoreHint.GetTopLeftForViewport(Bounds, new Size(formattedText.Width, formattedText.Height)));
         }
 
         base.Render(context);
 
-        // Request next frame as soon as possible, if the game is running. Remember to reset the stopwatch.
+        // Request the next frame as soon as possible if the game is running. Remember to reset the stopwatch.
         if (IsRunning)
         {
-            Dispatcher.UIThread.Post(InvalidateVisual, DispatcherPriority.Background);
+            Dispatcher.UIThread.Post(InvalidateVisual, DispatcherPriority.Render);
             _stopwatch.Restart();
         }
     }
 
+    /// <inheritdoc />
+    protected override void OnPointerEntered(PointerEventArgs e)
+    {
+        HitTestSnowFlakes(e.GetPosition(this));
+
+        base.OnPointerEntered(e);
+    }
+
+    /// <inheritdoc />
+    protected override void OnPointerMoved(PointerEventArgs e)
+    {
+        HitTestSnowFlakes(e.GetPosition(this));
+
+        base.OnPointerMoved(e);
+    }
+
     /// <summary>
-    /// This method is needed to customize hit-testing. In our case we want the pointer hit only in case
-    /// the game is running and the pointer is directly over one of our snowflakes.
+    /// This method will check if the pointer has hit any snowflake. If so, it will remove the snowflake from the list
+    /// and update the score.
     /// </summary>
     /// <param name="point">the pointer point to test.</param>
-    /// <returns>true if the pointer hit the control, otherwise false</returns>
-    /// <remarks>Used by the <see cref="ICustomHitTest"/>-interface, which this control implements.</remarks>
-    public bool HitTest(Point point)
+    private void HitTestSnowFlakes(Point point)
     {
-        if (!IsRunning) return false;
+        // if the game is not running, we don't need to do anything.
+        if (!IsRunning) return;
 
-        var snowFlake = Snowflakes.FirstOrDefault(x => x.IsHit(point, Bounds));
-        if (snowFlake != null)
+        // loop through all snowflakes and check if the pointer is inside one of them.
+        // Copy the list to avoid concurrent modification exceptions.
+        foreach (var snowFlake in Snowflakes.ToArray())
         {
-            Snowflakes.Remove(snowFlake);
-            Score += snowFlake.GetHitScore();
-            
-            // Add a text hint about the earned score. We also hand over the containing collection,
-            // so it can auto-remove itself after 1 second.
-            _scoreHintsCollection.Add(new ScoreHint(snowFlake, _scoreHintsCollection));
-        }
+            if (snowFlake.IsHit(point, Bounds))
+            {
+                Snowflakes.Remove(snowFlake);
+                Score += snowFlake.GetHitScore();
 
-        return snowFlake != null;
+                // Add a text hint about the earned score. We also hand over the containing collection,
+                // so it can auto-remove itself after 1 second.
+                _scoreHintsCollection.Add(new ScoreHint(snowFlake, _scoreHintsCollection));
+            }
+        }
     }
 }

src/Avalonia.Samples/CustomControls/SnowflakesControlSample/README.adoc

@@ -273,7 +273,7 @@ Here is the final class: xref:ViewModels/SnowflakeGameViewModel.cs[]
 
 === Step 3: Add the SnowflakesControl
 
-Now it's time to add the needed `Control` to render our game. Therefore, we add a new folder `Controls` and inside we add a new class `SnowflakesControl.cs`. This class must inherit `Control`. In addition, we want to implement the interface `ICustomHitTest` in order to control hit-testing on our own.
+Now it's time to add the needed `Control` to render our game. Therefore, we add a new folder `Controls` and inside we add a new class `SnowflakesControl.cs`. This class must inherit `Control`. 
 
 The control needs some https://docs.avaloniaui.net/docs/guides/custom-controls/how-to-create-advanced-custom-controls[[AvaloniaProperties\]] to allow us to bind to it.
 
@@ -374,7 +374,7 @@ public override void Render(DrawingContext context)
     // Request next frame as soon as possible, if the game is running. Remember to reset the stopwatch.
     if (IsRunning)
     {
-        Dispatcher.UIThread.Post(InvalidateVisual, DispatcherPriority.Background);
+        Dispatcher.UIThread.Post(InvalidateVisual, DispatcherPriority.Render);
         _stopwatch.Restart();
     }
 }
@@ -387,31 +387,56 @@ This is how a single render frame would look like:
 .Result of a single render loop
 image:_docs/single_render_frame.png[]
 
-As we wanted to implement `ICustomHitTest`, we will add the needed interface members, which is just the following method here:
+As we want to check if our pointer is over any `Snowflake`, we will override the `OnPointerEntered` and `OnPointerMoved` methods. From the `PointerEventArgs` we can read the pointer position and forward it to a method that tests for hits,
 
 [source,csharp]
 ----
-public bool HitTest(Point point)
+/// <inheritdoc />
+protected override void OnPointerEntered(PointerEventArgs e)
 {
-    if (!IsRunning) return false;
+    HitTestSnowFlakes(e.GetPosition(this));
+    base.OnPointerEntered(e);
+}
+
+/// <inheritdoc />
+protected override void OnPointerMoved(PointerEventArgs e)
+{
+    HitTestSnowFlakes(e.GetPosition(this));
+    base.OnPointerMoved(e);
+}
+
+/// <summary>
+/// This method will check if the pointer has hit any snowflake. If so, it will remove the snowflake from the list
+/// and update the score.
+/// </summary>
+/// <param name="point">the pointer point to test.</param>
+private void HitTestSnowFlakes(Point point)
+{
+    // if the game is not running, we don't need to do anything.
+    if (!IsRunning) return;
 
-    var snowFlake = Snowflakes.FirstOrDefault(x => x.IsHit(point, Bounds));
-    if (snowFlake != null)
+    // loop through all snowflakes and check if the pointer is inside one of them.
+    // Copy the list to avoid concurrent modification exceptions.
+    foreach (var snowFlake in Snowflakes.ToArray())
     {
-        Snowflakes.Remove(snowFlake);
-        Score += snowFlake.GetHitScore();
-    }
+        if (snowFlake.IsHit(point, Bounds))
+        {
+            Snowflakes.Remove(snowFlake);
+            Score += snowFlake.GetHitScore();
 
-    return snowFlake != null;
+            // Add a text hint about the earned score. We also hand over the containing collection,
+            // so it can auto-remove itself after 1 second.
+            _scoreHintsCollection.Add(new ScoreHint(snowFlake, _scoreHintsCollection));
+        }
+    }
 }
 ----
 
 What this method does is:
 
-* If the game is not running, the control shouldn't receive any hit
-* If the game is running, search for any snowflake hit by the pointer
-** If one is found, remove it from the collection
-** If one is found, add the score to the total score
+* If the game is running, search for all snowflakes hit by the pointer
+** If any is found, remove it from the collection
+** If any is found, add the score to the total score
 
 Here is the final class xref:Controls/SnowflakesControl.cs[]