From 94f4083b70da72bbe2794b4c4db981ce43a37a11 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Tue, 16 Jul 2024 22:13:30 +1000
Subject: [PATCH] Fix filtering on PNG encode.

---
 src/ImageSharp/Formats/Png/Filters/AverageFilter.cs | 4 ++--
 src/ImageSharp/Formats/Png/Filters/SubFilter.cs     | 7 ++++---
 src/ImageSharp/Formats/Png/Filters/UpFilter.cs      | 4 ++--
 src/ImageSharp/Formats/Png/PngEncoderCore.cs        | 6 +++++-
 4 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/ImageSharp/Formats/Png/Filters/AverageFilter.cs b/src/ImageSharp/Formats/Png/Filters/AverageFilter.cs
index 2750aa6808..57c2029181 100644
--- a/src/ImageSharp/Formats/Png/Filters/AverageFilter.cs
+++ b/src/ImageSharp/Formats/Png/Filters/AverageFilter.cs
@@ -169,7 +169,7 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> previo
             Vector256<int> sumAccumulator = Vector256<int>.Zero;
             Vector256<byte> allBitsSet = Avx2.CompareEqual(sumAccumulator, sumAccumulator).AsByte();
 
-            for (nuint xLeft = x - bytesPerPixel; x <= (uint)(scanline.Length - Vector256<byte>.Count); xLeft += (uint)Vector256<byte>.Count)
+            for (nuint xLeft = x - bytesPerPixel; (int)x <= scanline.Length - Vector256<byte>.Count; xLeft += (uint)Vector256<byte>.Count)
             {
                 Vector256<byte> scan = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector256<byte> left = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref scanBaseRef, xLeft));
@@ -192,7 +192,7 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> previo
             Vector128<int> sumAccumulator = Vector128<int>.Zero;
             Vector128<byte> allBitsSet = Sse2.CompareEqual(sumAccumulator, sumAccumulator).AsByte();
 
-            for (nuint xLeft = x - bytesPerPixel; x <= (uint)(scanline.Length - Vector128<byte>.Count); xLeft += (uint)Vector128<byte>.Count)
+            for (nuint xLeft = x - bytesPerPixel; (int)x <= scanline.Length - Vector128<byte>.Count; xLeft += (uint)Vector128<byte>.Count)
             {
                 Vector128<byte> scan = Unsafe.As<byte, Vector128<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector128<byte> left = Unsafe.As<byte, Vector128<byte>>(ref Unsafe.Add(ref scanBaseRef, xLeft));
diff --git a/src/ImageSharp/Formats/Png/Filters/SubFilter.cs b/src/ImageSharp/Formats/Png/Filters/SubFilter.cs
index d58ac6fb7b..1af4a3b729 100644
--- a/src/ImageSharp/Formats/Png/Filters/SubFilter.cs
+++ b/src/ImageSharp/Formats/Png/Filters/SubFilter.cs
@@ -136,7 +136,7 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> result
             Vector256<byte> zero = Vector256<byte>.Zero;
             Vector256<int> sumAccumulator = Vector256<int>.Zero;
 
-            for (nuint xLeft = x - (uint)bytesPerPixel; x <= (uint)(scanline.Length - Vector256<byte>.Count); xLeft += (uint)Vector256<byte>.Count)
+            for (nuint xLeft = x - (uint)bytesPerPixel; (int)x <= (scanline.Length - Vector256<byte>.Count); xLeft += (uint)Vector256<byte>.Count)
             {
                 Vector256<byte> scan = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector256<byte> prev = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref scanBaseRef, xLeft));
@@ -150,11 +150,12 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> result
 
             sum += Numerics.EvenReduceSum(sumAccumulator);
         }
-        else if (Vector.IsHardwareAccelerated)
+        else
+        if (Vector.IsHardwareAccelerated)
         {
             Vector<uint> sumAccumulator = Vector<uint>.Zero;
 
-            for (nuint xLeft = x - (uint)bytesPerPixel; x <= (uint)(scanline.Length - Vector<byte>.Count); xLeft += (uint)Vector<byte>.Count)
+            for (nuint xLeft = x - (uint)bytesPerPixel; (int)x <= (scanline.Length - Vector<byte>.Count); xLeft += (uint)Vector<byte>.Count)
             {
                 Vector<byte> scan = Unsafe.As<byte, Vector<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector<byte> prev = Unsafe.As<byte, Vector<byte>>(ref Unsafe.Add(ref scanBaseRef, xLeft));
diff --git a/src/ImageSharp/Formats/Png/Filters/UpFilter.cs b/src/ImageSharp/Formats/Png/Filters/UpFilter.cs
index dd3c2d8612..405d89e6c1 100644
--- a/src/ImageSharp/Formats/Png/Filters/UpFilter.cs
+++ b/src/ImageSharp/Formats/Png/Filters/UpFilter.cs
@@ -179,7 +179,7 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> previo
             Vector256<byte> zero = Vector256<byte>.Zero;
             Vector256<int> sumAccumulator = Vector256<int>.Zero;
 
-            for (; x <= (uint)(scanline.Length - Vector256<byte>.Count);)
+            for (; (int)x <= scanline.Length - Vector256<byte>.Count;)
             {
                 Vector256<byte> scan = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector256<byte> above = Unsafe.As<byte, Vector256<byte>>(ref Unsafe.Add(ref prevBaseRef, x));
@@ -197,7 +197,7 @@ public static void Encode(ReadOnlySpan<byte> scanline, ReadOnlySpan<byte> previo
         {
             Vector<uint> sumAccumulator = Vector<uint>.Zero;
 
-            for (; x <= (uint)(scanline.Length - Vector<byte>.Count);)
+            for (; (int)x <= scanline.Length - Vector<byte>.Count;)
             {
                 Vector<byte> scan = Unsafe.As<byte, Vector<byte>>(ref Unsafe.Add(ref scanBaseRef, x));
                 Vector<byte> above = Unsafe.As<byte, Vector<byte>>(ref Unsafe.Add(ref prevBaseRef, x));
diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
index 802e4dd6a4..ca345475a7 100644
--- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs
@@ -1477,7 +1477,11 @@ private void SanitizeAndSetEncoderOptions<TPixel>(
         // Use options, then check metadata, if nothing set there then we suggest
         // a sensible default based upon the pixel format.
         this.colorType = encoder.ColorType ?? pngMetadata.ColorType ?? SuggestColorType<TPixel>();
-        if (!encoder.FilterMethod.HasValue)
+        if (encoder.FilterMethod.HasValue)
+        {
+            this.filterMethod = encoder.FilterMethod.Value;
+        }
+        else
         {
             // Specification recommends default filter method None for paletted images and Paeth for others.
             this.filterMethod = this.colorType is PngColorType.Palette ? PngFilterMethod.None : PngFilterMethod.Paeth;