Merge pull request #1699 from cwensley/curtis/wpf-graphics-on-bitmap-…

…is-slow

Wpf: Fix huge performance penalty using Graphics on many Bitmaps

src/Eto.Wpf/WpfExtensions.cs

@@ -330,7 +330,11 @@ public static void RenderWithCollect(this swm.Imaging.RenderTargetBitmap bitmap,
 			// fix memory leak with RenderTargetBitmap.  See http://stackoverflow.com/questions/14786490/wpf-memory-leak-using-rendertargetbitmap
 			// Reproducible with the 
 			// GC.Collect alone seems to fix the issue.  Adding GC.WaitForPendingFinalizers may impact performance.
-			GC.Collect();
+
+			// Note: this may no longer be an issue with the latest version of .NET after some testing, however
+			// we keep it here to keep memory in check, but instead make it non-blocking so it doesn't cause a huge
+			// performance penalty creating many Bitmaps with a Graphics object.
+			GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, false);
 		}
 
 

test/Eto.Test.Wpf/UnitTests/BitmapTests.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Diagnostics;
+using Eto.Drawing;
+using Eto.Test.UnitTests;
+using NUnit.Framework;
+
+namespace Eto.Test.Wpf.UnitTests
+{
+	[TestFixture]
+	public class BitmapTests : TestBase
+	{
+		[Test, Timeout(1000)]
+		public void CreatingManySmallBitmapsShouldBeFast()
+		{
+			var sw = new Stopwatch();
+			sw.Start();
+			for (int i = 0; i < 100; i++)
+			{
+				var bmp = new Bitmap(20, 20, PixelFormat.Format32bppRgba);
+
+				using (var g = new Graphics(bmp))
+				{
+					g.Clear(Colors.Blue);
+				}
+			}
+			sw.Stop();
+			Console.WriteLine($"Total time: {sw.Elapsed}");
+		}
+
+	}
+}