add to render demo

samples/RenderDemo/Controls/LineBoundsDemoControl.cs

@@ -0,0 +1,46 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Media;
+using Avalonia.Rendering.SceneGraph;
+using Avalonia.Threading;
+
+namespace RenderDemo.Controls
+{
+    public class LineBoundsDemoControl : Control
+    {
+        private double angle = Math.PI / 8;
+
+        public static double CalculateOppSide(double angle, double hyp)
+        {
+            return Math.Sin(angle) * hyp;
+        }
+
+        public static double CalculateAdjSide(double angle, double hyp)
+        {
+            return Math.Cos(angle) * hyp;
+        }
+
+        public override void Render(DrawingContext drawingContext)
+        {
+            var lineLength = Math.Sqrt((100 * 100) + (100 * 100));
+
+            var diffX = CalculateAdjSide(angle, lineLength);
+            var diffY = CalculateOppSide(angle, lineLength);
+
+
+            var p1 = new Point(200, 200);
+            var p2 = new Point(p1.X + diffX, p1.Y + diffY);
+
+            var pen = new Pen(Brushes.Green, 20, lineCap: PenLineCap.Square);
+            var boundPen = new Pen(Brushes.Black);
+
+            drawingContext.DrawLine(pen, p1, p2);
+
+            drawingContext.DrawRectangle(boundPen, LineBoundsHelper.CalculateBounds(p1, p2, pen));
+
+            angle += Math.PI / 360;
+            Dispatcher.UIThread.Post(InvalidateVisual, DispatcherPriority.Background);
+        }
+    }
+}

samples/RenderDemo/MainWindow.xaml

@@ -44,6 +44,9 @@
       <TabItem Header="GlyphRun">
         <pages:GlyphRunPage/>
       </TabItem>
+      <TabItem Header="LineBoundsDemo">
+        <pages:LineBoundsDemo />
+      </TabItem>
     </TabControl>
   </DockPanel>
 </Window>

samples/RenderDemo/Pages/LineBoundsDemo.xaml

@@ -0,0 +1,9 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             xmlns:controls="clr-namespace:RenderDemo.Controls"
+             x:Class="RenderDemo.Pages.LineBoundsDemo">
+  <controls:LineBoundsDemoControl />
+</UserControl>

samples/RenderDemo/Pages/LineBoundsDemo.xaml.cs

@@ -0,0 +1,19 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace RenderDemo.Pages
+{
+    public class LineBoundsDemo : UserControl
+    {
+        public LineBoundsDemo()
+        {
+            this.InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+}