From 128c0b86989e5053aed3a671d12a373d1b0e3b9d Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Fri, 5 Jun 2020 17:16:48 +0100
Subject: [PATCH 1/2] Swap buffers. Fix #1211

---
 src/ImageSharp/Formats/Png/PngEncoderCore.cs  |  4 ++
 .../Formats/Png/PngEncoderTests.cs            | 47 +++++++++++--------
 2 files changed, 31 insertions(+), 20 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index a25f51fe1..5f7dd212f 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1081,6 +1081,10 @@ namespace SixLabors.ImageSharp.Formats.Png
                         // encode data
                         IManagedByteBuffer r = this.EncodeAdam7IndexedPixelRow(destSpan);
                         deflateStream.Write(r.Array, 0, resultLength);
+
+                        IManagedByteBuffer temp = this.currentScanline;
+                        this.currentScanline = this.previousScanline;
+                        this.previousScanline = temp;
                     }
                 }
             }
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 4f2490f9a..04f2ba7e0 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -199,17 +199,20 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
                 return;
             }
 
-            foreach (PngInterlaceMode interlaceMode in InterlaceMode)
+            foreach (var filterMethod in PngFilterMethods)
             {
-                TestPngEncoderCore(
-                provider,
-                pngColorType,
-                PngFilterMethod.Adaptive,
-                pngBitDepth,
-                interlaceMode,
-                appendPngColorType: true,
-                appendPixelType: true,
-                appendPngBitDepth: true);
+                foreach (PngInterlaceMode interlaceMode in InterlaceMode)
+                {
+                    TestPngEncoderCore(
+                    provider,
+                    pngColorType,
+                    (PngFilterMethod)filterMethod[0],
+                    pngBitDepth,
+                    interlaceMode,
+                    appendPngColorType: true,
+                    appendPixelType: true,
+                    appendPngBitDepth: true);
+                }
             }
         }
 
@@ -232,18 +235,22 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
         public void WorksWithAllBitDepthsAndExcludeAllFilter<TPixel>(TestImageProvider<TPixel> provider, PngColorType pngColorType, PngBitDepth pngBitDepth)
           where TPixel : unmanaged, IPixel<TPixel>
         {
-            foreach (PngInterlaceMode interlaceMode in InterlaceMode)
+            foreach (var filterMethod in PngFilterMethods)
             {
-                TestPngEncoderCore(
-                provider,
                 pngColorType,
-                PngFilterMethod.Adaptive,
-                pngBitDepth,
-                interlaceMode,
-                appendPngColorType: true,
-                appendPixelType: true,
-                appendPngBitDepth: true,
-                optimizeMethod: PngChunkFilter.ExcludeAll);
+                foreach (PngInterlaceMode interlaceMode in InterlaceMode)
+                {
+                    TestPngEncoderCore(
+                    provider,
+                    pngColorType,
+                    (PngFilterMethod)filterMethod[0],
+                    pngBitDepth,
+                    interlaceMode,
+                    appendPngColorType: true,
+                    appendPixelType: true,
+                    appendPngBitDepth: true,
+                    optimizeMethod: PngChunkFilter.ExcludeAll);
+                }
             }
         }
 

From 75be04657a71b26a2f4ea2471bcc1687d7451776 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Fri, 5 Jun 2020 17:17:29 +0100
Subject: [PATCH 2/2] Update PngEncoderTests.cs

---
 tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
index 04f2ba7e0..93ea73eb4 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs
@@ -237,7 +237,6 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
         {
             foreach (var filterMethod in PngFilterMethods)
             {
-                pngColorType,
                 foreach (PngInterlaceMode interlaceMode in InterlaceMode)
                 {
                     TestPngEncoderCore(