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Merged
maxkatz6 merged 1 commit into from
Dec 26, 2025
Merged

Don't use ICustomHitTest #235

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80 changes: 49 additions & 31 deletions src/Avalonia.Samples/CustomControls/SnowflakesControlSample/Controls/SnowflakesControl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand All @@ -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>();

Expand Down Expand Up @@ -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>
Expand All @@ -69,7 +69,7 @@ public IList<Snowflake> Snowflakes
}

private int _score;

/// <summary>
/// Gets or sets the current user score.
/// </summary>
Expand All @@ -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>
Expand All @@ -87,7 +87,7 @@ public bool IsRunning
get { return GetValue(IsRunningProperty); }
set { SetValue(IsRunningProperty, value); }
}

/// <inheritdoc />
protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
{
Expand All @@ -100,7 +100,7 @@ protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs chang
{
// Resets and starts the stopwatch
_stopwatch.Restart();

// Clear any previous score hints
_scoreHintsCollection.Clear();
}
Expand Down Expand Up @@ -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())
{
Expand All @@ -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(
Expand All @@ -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));
}
}
}
}
55 changes: 40 additions & 15 deletions src/Avalonia.Samples/CustomControls/SnowflakesControlSample/README.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -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.

Expand Down Expand Up @@ -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();
}
}
Expand All @@ -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[]

Expand Down