Some changes to make the usages of GDI in benchmarks and tests more stable, this should hopefully prevent "a generic error occurred in GDI+". Hopefully I didn't miss one... (#835)

tests/ImageSharp.Benchmarks/Drawing/DrawBeziers.cs

@@ -26,7 +26,8 @@ namespace SixLabors.ImageSharp.Benchmarks
                 {
                     graphics.InterpolationMode = InterpolationMode.Default;
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    Pen pen = new Pen(System.Drawing.Color.HotPink, 10);
+                    using (var pen = new Pen(System.Drawing.Color.HotPink, 10))
+                    {
                         graphics.DrawBeziers(pen, new[] {
                                                                 new PointF(10, 500),
                                                                 new PointF(30, 10),
@@ -34,6 +35,7 @@ namespace SixLabors.ImageSharp.Benchmarks
                                                                 new PointF(300, 500)
                                                             });
                     }
+                }
 
                 using (MemoryStream ms = new MemoryStream())
                 {

tests/ImageSharp.Benchmarks/Drawing/DrawLines.cs

@@ -26,13 +26,15 @@ namespace SixLabors.ImageSharp.Benchmarks
                 {
                     graphics.InterpolationMode = InterpolationMode.Default;
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    var pen = new Pen(System.Drawing.Color.HotPink, 10);
+                    using (var pen = new Pen(System.Drawing.Color.HotPink, 10))
+                    {
                         graphics.DrawLines(pen, new[] {
                                                               new PointF(10, 10),
                                                               new PointF(550, 50),
                                                               new PointF(200, 400)
                                                           });
                     }
+                }
 
                 using (var ms = new MemoryStream())
                 {

tests/ImageSharp.Benchmarks/Drawing/DrawPolygon.cs

@@ -26,13 +26,15 @@ namespace SixLabors.ImageSharp.Benchmarks
                 {
                     graphics.InterpolationMode = InterpolationMode.Default;
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    Pen pen = new Pen(System.Drawing.Color.HotPink, 10);
+                    using (var pen = new Pen(System.Drawing.Color.HotPink, 10))
+                    {
                         graphics.DrawPolygon(pen, new[] {
                                                                 new PointF(10, 10),
                                                                 new PointF(550, 50),
                                                                 new PointF(200, 400)
                                                             });
                     }
+                }
 
                 using (MemoryStream ms = new MemoryStream())
                 {

tests/ImageSharp.Benchmarks/Drawing/DrawText.cs

@@ -35,12 +35,13 @@ namespace SixLabors.ImageSharp.Benchmarks
                 {
                     graphics.InterpolationMode = InterpolationMode.Default;
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    Pen pen = new Pen(System.Drawing.Color.HotPink, 10);
+                    using (var font = new Font("Arial", 12, GraphicsUnit.Point))
-                    var font = new Font("Arial", 12, GraphicsUnit.Point);
+                    {
                         graphics.DrawString(TextToRender, font, System.Drawing.Brushes.HotPink, new RectangleF(10, 10, 780, 780));
                     }
                 }
             }
+        }
 
 
         [Benchmark(Description = "ImageSharp Draw Text - Cached Glyphs")]

tests/ImageSharp.Benchmarks/Drawing/DrawTextOutline.cs

@@ -34,14 +34,16 @@ namespace SixLabors.ImageSharp.Benchmarks
                 {
                     graphics.InterpolationMode = InterpolationMode.Default;
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    Pen pen = new Pen(System.Drawing.Color.HotPink, 10);
+                    using (var pen = new Pen(System.Drawing.Color.HotPink, 10))
-                    var font = new Font("Arial", 12, GraphicsUnit.Point);
+                    using (var font = new Font("Arial", 12, GraphicsUnit.Point))
-                    var gp = new GraphicsPath();
+                    using (var gp = new GraphicsPath())
+                    {
                         gp.AddString(TextToRender, font.FontFamily, (int)font.Style, font.Size, new RectangleF(10, 10, 780, 780), new StringFormat());
                         graphics.DrawPath(pen, gp);
                     }
                 }
             }
+        }
 
         [Benchmark(Description = "ImageSharp Draw Text Outline - Cached Glyphs")]
         public void DrawTextCore()

tests/ImageSharp.Benchmarks/Drawing/FillWithPattern.cs

@@ -26,9 +26,11 @@ namespace SixLabors.ImageSharp.Benchmarks
                 using (Graphics graphics = Graphics.FromImage(destination))
                 {
                     graphics.SmoothingMode = SmoothingMode.AntiAlias;
-                    HatchBrush brush = new HatchBrush(HatchStyle.BackwardDiagonal, Color.HotPink);
+                    using (var brush = new HatchBrush(HatchStyle.BackwardDiagonal, Color.HotPink))
+                    {
                         graphics.FillRectangle(brush, new Rectangle(0, 0, 800, 800)); // can't find a way to flood fill with a brush
                     }
+                }
                 using (MemoryStream ms = new MemoryStream())
                 {
                     destination.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);

tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/SystemDrawingBridge.cs

@@ -39,12 +39,14 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
             }
 
             BitmapData data = bmp.LockBits(fullRect, ImageLockMode.ReadWrite, bmp.PixelFormat);
+            var image = new Image<TPixel>(w, h);
+            try
+            {
                 byte* sourcePtrBase = (byte*)data.Scan0;
 
                 long sourceRowByteCount = data.Stride;
                 long destRowByteCount = w * sizeof(Bgra32);
 
-            var image = new Image<TPixel>(w, h);
                 Configuration configuration = image.GetConfiguration();
 
                 using (IMemoryOwner<Bgra32> workBuffer = Configuration.Default.MemoryAllocator.Allocate<Bgra32>(w))
@@ -65,6 +67,11 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
                         }
                     }
                 }
+            }
+            finally
+            {
+                bmp.UnlockBits(data);
+            }
 
             return image;
         }
@@ -91,12 +98,14 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
             }
 
             BitmapData data = bmp.LockBits(fullRect, ImageLockMode.ReadWrite, bmp.PixelFormat);
+            var image = new Image<TPixel>(w, h);
+            try
+            {
                 byte* sourcePtrBase = (byte*)data.Scan0;
 
                 long sourceRowByteCount = data.Stride;
                 long destRowByteCount = w * sizeof(Bgr24);
 
-            var image = new Image<TPixel>(w, h);
                 Configuration configuration = image.GetConfiguration();
 
                 using (IMemoryOwner<Bgr24> workBuffer = Configuration.Default.MemoryAllocator.Allocate<Bgr24>(w))
@@ -110,14 +119,15 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
                             byte* sourcePtr = sourcePtrBase + (data.Stride * y);
 
                             Buffer.MemoryCopy(sourcePtr, destPtr, destRowByteCount, sourceRowByteCount);
-                        PixelOperations<TPixel>.Instance.FromBgr24(
+                            PixelOperations<TPixel>.Instance.FromBgr24(configuration, workBuffer.GetSpan().Slice(0, w), row);
-                            configuration,
-                            workBuffer.GetSpan().Slice(0, w),
-                            row);
                         }
                     }
                 }
-
+            }
+            finally
+            {
+                bmp.UnlockBits(data);
+            }
             return image;
         }
 
@@ -131,6 +141,8 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
             var resultBitmap = new Bitmap(w, h, PixelFormat.Format32bppArgb);
             var fullRect = new Rectangle(0, 0, w, h);
             BitmapData data = resultBitmap.LockBits(fullRect, ImageLockMode.ReadWrite, resultBitmap.PixelFormat);
+            try
+            {
                 byte* destPtrBase = (byte*)data.Scan0;
 
                 long destRowByteCount = data.Stride;
@@ -150,8 +162,11 @@ namespace SixLabors.ImageSharp.Tests.TestUtilities.ReferenceCodecs
                         }
                     }
                 }
-
+            }
+            finally
+            {
                 resultBitmap.UnlockBits(data);
+            }
 
             return resultBitmap;
         }