Move PngHeader writing logic to struct

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -606,16 +606,9 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="header">The <see cref="PngHeader"/>.</param>
         private void WriteHeaderChunk(Stream stream, in PngHeader header)
         {
-            BinaryPrimitives.WriteInt32BigEndian(this.chunkDataBuffer.AsSpan(0, 4), header.Width);
-            BinaryPrimitives.WriteInt32BigEndian(this.chunkDataBuffer.AsSpan(4, 4), header.Height);
+            header.WriteTo(this.chunkDataBuffer);
 
-            this.chunkDataBuffer[8] = header.BitDepth;
-            this.chunkDataBuffer[9] = (byte)header.ColorType;
-            this.chunkDataBuffer[10] = header.CompressionMethod;
-            this.chunkDataBuffer[11] = header.FilterMethod;
-            this.chunkDataBuffer[12] = (byte)header.InterlaceMethod;
-
-            this.WriteChunk(stream, PngChunkType.Header, this.chunkDataBuffer, 0, 13);
+            this.WriteChunk(stream, PngChunkType.Header, this.chunkDataBuffer, 0, PngHeader.Size);
         }
 
         /// <summary>
@@ -697,28 +690,24 @@ namespace SixLabors.ImageSharp.Formats.Png
             switch (meta.ResolutionUnits)
             {
                 case PixelResolutionUnit.AspectRatio:
-
                     this.chunkDataBuffer[8] = 0;
                     BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(meta.HorizontalResolution));
                     BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(meta.VerticalResolution));
                     break;
 
                 case PixelResolutionUnit.PixelsPerInch:
-
                     this.chunkDataBuffer[8] = 1; // Per meter
                     BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(UnitConverter.InchToMeter(meta.HorizontalResolution)));
                     BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(UnitConverter.InchToMeter(meta.VerticalResolution)));
                     break;
 
                 case PixelResolutionUnit.PixelsPerCentimeter:
-
                     this.chunkDataBuffer[8] = 1; // Per meter
                     BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(UnitConverter.CmToMeter(meta.HorizontalResolution)));
                     BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(UnitConverter.CmToMeter(meta.VerticalResolution)));
                     break;
 
                 default:
-
                     this.chunkDataBuffer[8] = 1; // Per meter
                     BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(meta.HorizontalResolution));
                     BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(meta.VerticalResolution));
@@ -782,26 +771,22 @@ namespace SixLabors.ImageSharp.Formats.Png
                     break;
 
                 case PngFilterMethod.Sub:
-
                     this.sub = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     break;
 
                 case PngFilterMethod.Up:
-
                     this.up = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     break;
 
                 case PngFilterMethod.Average:
-
                     this.average = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     break;
 
                 case PngFilterMethod.Paeth:
-
                     this.paeth = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     break;
-                case PngFilterMethod.Adaptive:
 
+                case PngFilterMethod.Adaptive:
                     this.sub = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     this.up = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);
                     this.average = this.memoryAllocator.AllocateManagedByteBuffer(resultLength, AllocationOptions.Clean);

src/ImageSharp/Formats/Png/PngHeader.cs

@@ -11,6 +11,8 @@ namespace SixLabors.ImageSharp.Formats.Png
     /// </summary>
     internal readonly struct PngHeader
     {
+        public const int Size = 13;
+
         public PngHeader(
             int width,
             int height,
@@ -78,6 +80,22 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// </summary>
         public PngInterlaceMode InterlaceMethod { get; }
 
+        /// <summary>
+        /// Writes the header to the given buffer.
+        /// </summary>
+        /// <param name="buffer">The buffer to write to.</param>
+        public void WriteTo(Span<byte> buffer)
+        {
+            BinaryPrimitives.WriteInt32BigEndian(buffer.Slice(0, 4), this.Width);
+            BinaryPrimitives.WriteInt32BigEndian(buffer.Slice(4, 4), this.Height);
+
+            buffer[8] = this.BitDepth;
+            buffer[9] = (byte)this.ColorType;
+            buffer[10] = this.CompressionMethod;
+            buffer[11] = this.FilterMethod;
+            buffer[12] = (byte)this.InterlaceMethod;
+        }
+
         /// <summary>
         /// Parses the PngHeader from the given data buffer.
         /// </summary>