ICustomDrawOperation.Render not being called after DrawingContext.Custom call

Describe the bug When implementing a custom draw operation via ICustomDrawOperation, its Render method isn’t always invoked when the associated control calls DrawingContext.Custom.

Minimal Issue Reproduction

public class SkiaCanvas : UserControl
{
    private class SkiaCallbackRenderOperation : ICustomDrawOperation
    {
        public Action<SKCanvas>? RenderCall;
        public Rect Bounds { get; set; }

        public void Dispose()
        {
        }

        public bool Equals(ICustomDrawOperation? other)
        {
            return false;
        }

        public bool HitTest(Point p)
        {
            return false;
        }

        public void Render(ImmediateDrawingContext context)
        {
            // This method is reached only when resizing the window or opening a menuitem over the control
            // No calls from Render, invoked via custom.Render reach this
            if (!context.TryGetFeature<ISkiaSharpApiLeaseFeature>(out var leaseFeature))
                throw new Exception("SkiaSharp is not supported.");

            using var lease = leaseFeature.Lease();

            RenderCall?.Invoke(lease.SkCanvas);
        }
    }

    public event Action<SkiaRenderEventArgs>? RenderSkia;
    private readonly SkiaCallbackRenderOperation _skiaCallbackRenderOperation;

    public SkiaCanvas()
    {
        _skiaCallbackRenderOperation = new SkiaCallbackRenderOperation
        {
            RenderCall = canvas =>
            {
                RenderSkia?.Invoke(new SkiaRenderEventArgs
                {
                    Sender = this,
                    Canvas = canvas
                });
            }
        };
        ClipToBounds = true;
    }


    public override void Render(DrawingContext context)
    {
        // This method (Render) is called at refresh rate, everything is fine

        _skiaCallbackRenderOperation.Bounds = new Rect(0, 0, DesiredSize.Width, DesiredSize.Height);

        // Jump into SkiaCallbackRenderOperation.Render
        context.Custom(_skiaCallbackRenderOperation);

        Dispatcher.UIThread.InvokeAsync(InvalidateVisual, DispatcherPriority.Background);
    }
}

Expected behavior ICustomDrawOperation.Render is executed when calling DrawingContext.Custom

[beto-rodriguez]

The render method will be called while the control is Invalid, Avalonia will call (or invalidate) the Render method for you when the size changes or the first time the control needs to render, then it is your responsibility to call the InvalidateVisual(); method to let Avalonia know that that control needs to be redrawn.

[maxkatz6]

I have run your code locally, and Bounds was not empty. Moreover, Bounds in general is a property you usually need to read when you want to get the current size of the control. As with any other control, actual bounds of the control depend on the parent panel (Grid, StackPanel, Canvas…they all will allocate size for a child differently) and control properties (Alignment, Min/MaxWidth/Height…)