share linebouds helper with render demo. remove hacky test code.

samples/RenderDemo/Controls/LineBoundsDemoControl.cs

@@ -9,24 +9,34 @@ namespace RenderDemo.Controls
 {
     public class LineBoundsDemoControl : Control
     {
-        private double angle = Math.PI / 8;
+        static LineBoundsDemoControl()
+        {
+            AffectsRender<LineBoundsDemoControl>(AngleProperty);
+        }
 
-        public static double CalculateOppSide(double angle, double hyp)
+        public LineBoundsDemoControl()
         {
-            return Math.Sin(angle) * hyp;
+            var timer = new DispatcherTimer();
+            timer.Interval = TimeSpan.FromSeconds(1 / 60);
+            timer.Tick += (sender, e) => Angle += Math.PI / 360;
+            timer.Start();
         }
 
-        public static double CalculateAdjSide(double angle, double hyp)
+        public static readonly StyledProperty<double> AngleProperty =
+            AvaloniaProperty.Register<LineBoundsDemoControl, double>(nameof(Angle));        
+
+        public double Angle
         {
-            return Math.Cos(angle) * hyp;
+            get => GetValue(AngleProperty);
+            set => SetValue(AngleProperty, value);
         }
 
         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 diffX = LineBoundsHelper.CalculateAdjSide(Angle, lineLength);
+            var diffY = LineBoundsHelper.CalculateOppSide(Angle, lineLength);
 
 
             var p1 = new Point(200, 200);
@@ -38,9 +48,6 @@ namespace RenderDemo.Controls
             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/RenderDemo.csproj

@@ -3,6 +3,9 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\..\src\Avalonia.Visuals\Rendering\SceneGraph\LineBoundsHelper.cs" Link="LineBoundsHelper.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\src\Avalonia.Diagnostics\Avalonia.Diagnostics.csproj" />
     <ProjectReference Include="..\..\src\Linux\Avalonia.LinuxFramebuffer\Avalonia.LinuxFramebuffer.csproj" />

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

@@ -3,7 +3,7 @@ using Avalonia.Media;
 
 namespace Avalonia.Rendering.SceneGraph
 {
-    public static class LineBoundsHelper
+    internal static class LineBoundsHelper
     {
         private static double CalculateAngle(Point p1, Point p2)
         {
@@ -13,12 +13,12 @@ namespace Avalonia.Rendering.SceneGraph
             return Math.Atan2(yDiff, xDiff);
         }
 
-        private static double CalculateOppSide(double angle, double hyp)
+        internal static double CalculateOppSide(double angle, double hyp)
         {
             return Math.Sin(angle) * hyp;
         }
 
-        private static double CalculateAdjSide(double angle, double hyp)
+        internal static double CalculateAdjSide(double angle, double hyp)
         {
             return Math.Cos(angle) * hyp;
         }