A little cleanup and comments

src/ImageSharp/Formats/README.md

@@ -0,0 +1,6 @@
+# Encoder/Decoder for true vision targa files
+
+Useful links for reference:
+
+- [FileFront](https://www.fileformat.info/format/tga/egff.htm)
+- [Tga Specification](http://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf)

src/ImageSharp/Formats/Tga/TgaDecoderCore.cs

@@ -50,6 +50,11 @@ namespace SixLabors.ImageSharp.Formats.Tga
         /// </summary>
         private readonly ITgaDecoderOptions options;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TgaDecoderCore"/> class.
+        /// </summary>
+        /// <param name="configuration">The configuration.</param>
+        /// <param name="options">The options.</param>
         public TgaDecoderCore(Configuration configuration, ITgaDecoderOptions options)
         {
             this.configuration = configuration;
@@ -183,6 +188,16 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a uncompressed TGA image with a palette.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="palette">The color palette.</param>
+        /// <param name="colorMapPixelSizeInBytes">Color map size of one entry in bytes.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadPaletted<TPixel>(int width, int height, Buffer2D<TPixel> pixels, byte[] palette, int colorMapPixelSizeInBytes, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -236,6 +251,16 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a run length encoded TGA image with a palette.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="palette">The color palette.</param>
+        /// <param name="colorMapPixelSizeInBytes">Color map size of one entry in bytes.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadPalettedRle<TPixel>(int width, int height, Buffer2D<TPixel> pixels, byte[] palette, int colorMapPixelSizeInBytes, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -279,6 +304,14 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a uncompressed monochrome TGA image.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadMonoChrome<TPixel>(int width, int height, Buffer2D<TPixel> pixels, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -298,6 +331,14 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a uncompressed TGA image where each pixels has 16 bit.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadBgra16<TPixel>(int width, int height, Buffer2D<TPixel> pixels, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -323,6 +364,14 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a uncompressed TGA image where each pixels has 24 bit.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadBgr24<TPixel>(int width, int height, Buffer2D<TPixel> pixels, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -342,6 +391,14 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a uncompressed TGA image where each pixels has 32 bit.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadBgra32<TPixel>(int width, int height, Buffer2D<TPixel> pixels, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -361,6 +418,15 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Reads a run length encoded TGA image.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="pixels">The <see cref="Buffer2D{TPixel}"/> to assign the palette to.</param>
+        /// <param name="bytesPerPixel">The bytes per pixel.</param>
+        /// <param name="inverted">Indicates, if the origin of the image is top left rather the bottom left (the default).</param>
         private void ReadRle<TPixel>(int width, int height, Buffer2D<TPixel> pixels, int bytesPerPixel, bool inverted)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -415,6 +481,13 @@ namespace SixLabors.ImageSharp.Formats.Tga
                 this.metadata);
         }
 
+        /// <summary>
+        /// Produce uncompressed tga data from a run length encoded stream.
+        /// </summary>
+        /// <param name="width">The width of the image.</param>
+        /// <param name="height">The height of the image.</param>
+        /// <param name="buffer">Buffer for uncompressed data.</param>
+        /// <param name="bytesPerPixel">The bytes used per pixel.</param>
         private void UncompressRle(int width, int height, Span<byte> buffer, int bytesPerPixel)
         {
             int uncompressedPixels = 0;
@@ -452,6 +525,16 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Helper method for decoding BGRA5551 images. Makes the pixels opaque, because the high bit does not
+        /// represent an alpha channel.
+        /// TODO: maybe there is a better/faster way to achieve this.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="pixels">The destination pixel buffer.</param>
+        /// <param name="currentPosition">The start position of pixel data.</param>
+        /// <param name="row">A byte array to store the read pixel data.</param>
+        /// <param name="bgraRowSpan">Bgra pixel row span.</param>
         private void MakeOpaque<TPixel>(Buffer2D<TPixel> pixels, long currentPosition, IManagedByteBuffer row, Span<Bgra5551> bgraRowSpan)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -477,6 +560,13 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Returns the y- value based on the given height.
+        /// </summary>
+        /// <param name="y">The y- value representing the current row.</param>
+        /// <param name="height">The height of the bitmap.</param>
+        /// <param name="inverted">Whether the bitmap is inverted.</param>
+        /// <returns>The <see cref="int"/> representing the inverted value.</returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static int Invert(int y, int height, bool inverted) => (!inverted) ? height - y - 1 : y;
 

src/ImageSharp/Formats/Tga/TgaEncoderCore.cs

@@ -51,6 +51,12 @@ namespace SixLabors.ImageSharp.Formats.Tga
             this.useCompression = options.Compress;
         }
 
+        /// <summary>
+        /// Encodes the image to the specified stream from the <see cref="ImageFrame{TPixel}"/>.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
+        /// <param name="stream">The <see cref="Stream"/> to encode the image data to.</param>
         public void Encode<TPixel>(Image<TPixel> image, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -135,6 +141,12 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Writes a run length encoded tga image to the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="stream">The stream to write the image to.</param>
+        /// <param name="image">The image to encode.</param>
         private void WriteRunLengthEndcodedImage<TPixel>(Stream stream, ImageFrame<TPixel> image)
             where TPixel : struct, IPixel<TPixel>
         {
@@ -184,6 +196,12 @@ namespace SixLabors.ImageSharp.Formats.Tga
             }
         }
 
+        /// <summary>
+        /// Finds consecutive pixels, which have the same value starting from the pixel span offset 0.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel type.</typeparam>
+        /// <param name="pixelSpan">The pixel span to search in.</param>
+        /// <returns>The number of equal pixels.</returns>
         private byte FindEqualPixels<TPixel>(Span<TPixel> pixelSpan)
             where TPixel : struct, IPixel<TPixel>
         {

src/ImageSharp/Formats/Tga/TgaImageType.cs

@@ -46,25 +46,4 @@ namespace SixLabors.
         /// </summary>
         RleBlackAndWhite = 11,
     }
-
-    /// <summary>
-    /// Extension methods for TgaImageType enum.
-    /// </summary>
-    public static class TgaImageTypeExtensions
-    {
-        /// <summary>
-        /// Checks if this tga image type is run length encoded.
-        /// </summary>
-        /// <param name="imageType">The tga image type.</param>
-        /// <returns>True, if this image type is run length encoded, otherwise false.</returns>
-        public static bool IsRunLengthEncoded(this TgaImageType imageType)
-        {
-            if (imageType is TgaImageType.RleColorMapped || imageType is TgaImageType.RleBlackAndWhite || imageType is TgaImageType.RleTrueColor)
-            {
-                return true;
-            }
-
-            return false;
-        }
-    }
 }

src/ImageSharp/Formats/Tga/TgaImageTypeExtensions.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// Extension methods for TgaImageType enum.
+    /// </summary>
+    public static class TgaImageTypeExtensions
+    {
+        /// <summary>
+        /// Checks if this tga image type is run length encoded.
+        /// </summary>
+        /// <param name="imageType">The tga image type.</param>
+        /// <returns>True, if this image type is run length encoded, otherwise false.</returns>
+        public static bool IsRunLengthEncoded(this TgaImageType imageType)
+        {
+            if (imageType is TgaImageType.RleColorMapped || imageType is TgaImageType.RleBlackAndWhite || imageType is TgaImageType.RleTrueColor)
+            {
+                return true;
+            }
+
+            return false;
+        }
+    }
+}