WPF: OnRender和Hit测试

Question

使用OnRender在屏幕上画图时，有没有办法对绘制的图形进行命中测试？

示例代码

    protected override void OnRender(System.Windows.Media.DrawingContext drawingContext)
    {
        base.OnRender(drawingContext);

        drawingContext.DrawRectangle(Brushes.Black, null, new Rect(50, 50, 100, 100));
    }

显然，一个人没有引用绘制的矩形，这将是执行命中测试所必需的，或者我错了吗？我知道我可以使用DrawingVisual，我只是好奇我的理解是否正确，使用OnRender绘制一些你不能对绘制的东西执行任何命中测试的东西？

Answer 1

你理解的没错，没有办法对你使用DrawingContext方法绘制的图形进行命中测试，因为它们没有在可视化树中表示为对象。

Answer 2

除非我完全误解了OP的问题，否则答案是肯定的，命中测试是基于在OnRender期间绘制的内容。您可以通过在覆盖OnRender的同一个类中覆盖OnMouseEnter来进行判断。在OnMouseEnter的覆盖中，尝试执行以下操作：

var htr = VisualTreeHelper.HitTest(this, e.GetPosition(this));
if (htr != null)
     System.Diagnostics.Debug.WriteLine("It's a hit!");

现在，我注意到您仍然在调用base.OnRender，这表明您正在尝试在Visual本来会呈现的内容之上进行绘制。那么，您不能做的是区分父类呈现的内容与您在重写中呈现的内容。但是，如果需要，只需将图形包含在它自己的Visual中即可。

Answer 3

我的快速解决方案。这在许多方面都不理想，但它作为一个开始对我来说是可行的。如果有必要，可以很容易地重构以提高性能。

    /// <summary>
    /// Provides basic hit testing
    /// </summary>
    public class RadarHitTestUtility
    {
        public Dictionary<Tuple<int,int>, HitContainer> HitStorage = new Dictionary<Tuple<int, int>, HitContainer>();

        public void AddEllipse(RadarObject radarObject, Point point, double x, double y)
        {
            // Geometry used for hit testing
            var elipse = new EllipseGeometry
            {
                Center = point,
                RadiusX = x,
                RadiusY = y,
            };

            var key = new Tuple<int, int>((int)point.X, (int)point.Y);

            var hit = new HitContainer
            {
                Geometry = elipse,
                Bounds = elipse.Bounds,
                RadarObject = radarObject
            };

            if(!HitStorage.ContainsKey(key))
                HitStorage.Add(key, hit);
        }

        /// <summary>
        /// Gets first radar object whose center point is within distance of point.
        /// </summary>
        public HitContainer GetSimpleHit(Point point, int distance = 5)
        {
            foreach (var hit in HitStorage)
            {
                if (Math.Abs(hit.Key.Item1 - point.X) <= distance && Math.Abs(hit.Key.Item2 - point.Y) <= distance)
                {
                    hit.Value.Intersection = IntersectionDetail.NotCalculated;
                    return hit.Value;
                }
            }
            return default(HitContainer);
        }

        /// <summary>
        /// Gets first radar object that contains point
        /// </summary>
        public HitContainer GetHit(Point point)
        {
            var PreCheckDistance = 50;

            foreach (var hit in HitStorage)
            {
                if (Math.Abs(hit.Key.Item1 - point.X) <= PreCheckDistance && Math.Abs(hit.Key.Item2 - point.Y) <= PreCheckDistance)
                {
                    if (hit.Value.Geometry.FillContains(point))
                    {
                        hit.Value.Intersection = IntersectionDetail.FullyInside;
                        return hit.Value;
                    }                    
                }
            }
            return default(HitContainer);
        }

        /// <summary>
        /// Gets first radar object that intersects with geometry
        /// </summary>
        public HitContainer GetHit(Geometry geometry)
        {
            var PreCheckDistance = 50;
            var GeometryCheckTolerance = 1;
            var center = geometry.Bounds.Center();

            foreach (var hit in HitStorage)
            {
                if (Math.Abs(hit.Key.Item1 - center.X) <= PreCheckDistance && Math.Abs(hit.Key.Item2 - center.Y) <= PreCheckDistance)
                {
                    var result = hit.Value.Geometry.FillContainsWithDetail(geometry, GeometryCheckTolerance, ToleranceType.Absolute);
                    if (result != IntersectionDetail.Empty)
                    {
                        hit.Value.Intersection = result;
                        return hit.Value;
                    }
                }
            }
            return default(HitContainer);
        }

        public class HitContainer
        {
            public RadarObject RadarObject { get; set; }
            public Geometry Geometry { get; set; }
            public Rect Bounds { get; set; }
            public IntersectionDetail Intersection { get; set; }
        }

        public void Clear()
        {
            HitStorage.Clear();
        }
    }

在控件中声明实例

public RadarHitTestUtility HitTester = new RadarHitTestUtility();

您需要在某个时刻调用Clear()，以便命中测试集合中只存在当前对象。

HitTester.Clear();

在OnRender()中，当您希望记录绘制调用以进行命中测试时，可以使用AddEllipse()进行记录。

HitTester.AddEllipse(radarObject, radarObject.Point, actorRadius, actorRadius);

以下是我调用命中检查的方法

    private void MouseDownHandler(object sender, MouseButtonEventArgs e)
    {
        IsMouseDown = true;
        Cursor = Cursors.Hand;
        DragInitialPosition = Mouse.GetPosition(this);
        DragInitialPanOffset = CanvasData.PanOffset;

        var hit = FindElementUnderClick(sender, e);
        if (hit != null)
        {
            SelectedItem = hit.RadarObject.Actor;
        }            
    }

    private RadarHitTestUtility.HitContainer FindElementUnderClick(object sender, MouseEventArgs e)
    {
        var position = e.GetPosition((UIElement)sender);            
        return HitTester.GetHit(position);
    }

如果您希望能够测试椭圆以外的形状，只需将适当的记录方法添加到RadarHitTestUtility中并调用它，就可以创建一种不同类型的几何图形进行测试。