Merge pull request #6746 from RomanSoloweow/master

LineNode hit test

src/Avalonia.Visuals/Rendering/SceneGraph/LineNode.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using Avalonia.Media;
 using Avalonia.Media.Immutable;
 using Avalonia.Platform;
@@ -82,8 +83,32 @@ namespace Avalonia.Rendering.SceneGraph
 
         public override bool HitTest(Point p)
         {
-            // TODO: Implement line hit testing.
-            return false;
+            var a = P1;
+            var b = P2;
+
+            //If dot1 or dot2 is negative, then the angle between the perpendicular and the segment is obtuse.
+            //The distance from a point to a straight line is defined as the
+            //length of the vector formed by the point and the closest point of the segment
+
+            Vector ap = p - a;
+            var dot1 = Vector.Dot(b - a, ap);
+
+            if (dot1 < 0)
+                return ap.Length <= Pen.Thickness / 2;
+
+            Vector bp = p - b;
+            var dot2 = Vector.Dot(a - b, bp);
+
+            if (dot2 < 0)
+                return bp.Length <= Pen.Thickness / 2;
+
+            var bXaX = b.X - a.X;
+            var bYaY = b.Y - a.Y;
+
+            var distance = (bXaX * (p.Y - a.Y) - bYaY * (p.X - a.X)) /
+                           (Math.Sqrt(bXaX * bXaX + bYaY * bYaY));
+
+            return Math.Abs(distance) <= Pen.Thickness / 2;
         }
     }
 }

tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/LineNodeTests.cs

@@ -0,0 +1,61 @@
+using System.Collections.Generic;
+using Avalonia.Media;
+using Avalonia.Rendering.SceneGraph;
+using Xunit;
+
+namespace Avalonia.Visuals.UnitTests.Rendering.SceneGraph
+{
+    public class LineNodeTests
+    {
+        [Fact]
+        public void HitTest_Should_Be_True()
+        {
+            var lineNode = new LineNode(
+                Matrix.Identity, 
+                new Pen(Brushes.Black, 3),
+                new Point(15, 15),
+                new Point(150, 150));
+
+
+            var pointsInside = new List<Point>()
+            {
+                new Point(14, 14),
+                new Point(15, 15),
+                new Point(32.1, 30),
+                new Point(30, 32.1),
+                new Point(150, 150),
+                new Point(151, 151),
+            };
+
+            foreach (var point in pointsInside)
+            {
+                Assert.True(lineNode.HitTest(point)); 
+            }
+        }
+        
+        [Fact]
+        public void HitTest_Should_Be_False()
+        {
+            var lineNode = new LineNode(
+                Matrix.Identity, 
+                new Pen(Brushes.Black, 3),
+                new Point(15, 15),
+                new Point(150, 150));
+
+
+            var pointsOutside= new List<Point>()
+            {
+                new Point(13.9, 13.9),
+                new Point(30, 32.2),
+                new Point(32.2, 30),
+                new Point(151.1, 151.1),
+                new Point(200, 200),
+            };
+
+            foreach (var point in pointsOutside)
+            {
+                Assert.False(lineNode.HitTest(point)); 
+            }
+        }
+    }
+}