Add support for decoding and encoding of TGA images

.gitattributes

@@ -93,6 +93,7 @@
 *.gif               binary
 *.jpg               binary
 *.png               binary
+*.tga               binary
 *.ttf               binary
 *.snk               binary
 

src/ImageSharp/Configuration.cs

@@ -8,6 +8,7 @@
 using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Formats.Jpeg;
 using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Formats.Tga;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Processing;
 using SixLabors.Memory;
@@ -150,6 +151,7 @@ public Configuration Clone()
         /// <see cref="JpegConfigurationModule"/>
         /// <see cref="GifConfigurationModule"/>
         /// <see cref="BmpConfigurationModule"/>.
+        /// <see cref="TgaConfigurationModule"/>.
         /// </summary>
         /// <returns>The default configuration of <see cref="Configuration"/>.</returns>
         internal static Configuration CreateDefaultInstance()
@@ -158,7 +160,8 @@ internal static Configuration CreateDefaultInstance()
                 new PngConfigurationModule(),
                 new JpegConfigurationModule(),
                 new GifConfigurationModule(),
-                new BmpConfigurationModule());
+                new BmpConfigurationModule(),
+                new TgaConfigurationModule());
         }
     }
 }

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -387,9 +387,10 @@ private void ReadRle24<TPixel>(Buffer2D<TPixel> pixels, int width, int height, b
                     if (rowHasUndefinedPixels)
                     {
                         // Slow path with undefined pixels.
+                        int rowStartIdx = y * width * 3;
                         for (int x = 0; x < width; x++)
                         {
-                            int idx = (y * width * 3) + (x * 3);
+                            int idx = rowStartIdx + (x * 3);
                             if (undefinedPixels[x, y])
                             {
                                 switch (this.options.RleSkippedPixelHandling)
@@ -418,9 +419,10 @@ private void ReadRle24<TPixel>(Buffer2D<TPixel> pixels, int width, int height, b
                     else
                     {
                         // Fast path without any undefined pixels.
+                        int rowStartIdx = y * width * 3;
                         for (int x = 0; x < width; x++)
                         {
-                            int idx = (y * width * 3) + (x * 3);
+                            int idx = rowStartIdx + (x * 3);
                             color.FromBgr24(Unsafe.As<byte, Bgr24>(ref bufferSpan[idx]));
                             pixelRow[x] = color;
                         }

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/ITgaDecoderOptions.cs

@@ -0,0 +1,12 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// The options for decoding tga images. Currently empty, but this may change in the future.
+    /// </summary>
+    internal interface ITgaDecoderOptions
+    {
+    }
+}

src/ImageSharp/Formats/Tga/ITgaEncoderOptions.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// Configuration options for use during tga encoding.
+    /// </summary>
+    internal interface ITgaEncoderOptions
+    {
+        /// <summary>
+        /// Gets the number of bits per pixel.
+        /// </summary>
+        TgaBitsPerPixel? BitsPerPixel { get; }
+
+        /// <summary>
+        /// Gets a value indicating whether run length compression should be used.
+        /// </summary>
+        bool Compress { get; }
+    }
+}

src/ImageSharp/Formats/Tga/TgaBitsPerPixel.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// Enumerates the available bits per pixel the tga encoder supports.
+    /// </summary>
+    public enum TgaBitsPerPixel : byte
+    {
+        /// <summary>
+        /// 8 bits per pixel. Each pixel consists of 1 byte.
+        /// </summary>
+        Pixel8 = 8,
+
+        /// <summary>
+        /// 16 bits per pixel. Each pixel consists of 2 bytes.
+        /// </summary>
+        Pixel16 = 16,
+
+        /// <summary>
+        /// 24 bits per pixel. Each pixel consists of 3 bytes.
+        /// </summary>
+        Pixel24 = 24,
+
+        /// <summary>
+        /// 32 bits per pixel. Each pixel consists of 4 bytes.
+        /// </summary>
+        Pixel32 = 32
+    }
+}

src/ImageSharp/Formats/Tga/TgaConfigurationModule.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// Registers the image encoders, decoders and mime type detectors for the tga format.
+    /// </summary>
+    public sealed class TgaConfigurationModule : IConfigurationModule
+    {
+        /// <inheritdoc/>
+        public void Configure(Configuration configuration)
+        {
+            configuration.ImageFormatsManager.SetEncoder(TgaFormat.Instance, new TgaEncoder());
+            configuration.ImageFormatsManager.SetDecoder(TgaFormat.Instance, new TgaDecoder());
+            configuration.ImageFormatsManager.AddImageFormatDetector(new TgaImageFormatDetector());
+        }
+    }
+}

src/ImageSharp/Formats/Tga/TgaConstants.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Collections.Generic;
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    internal static class TgaConstants
+    {
+        /// <summary>
+        /// The list of mimetypes that equate to a targa file.
+        /// </summary>
+        public static readonly IEnumerable<string> MimeTypes = new[] { "image/x-tga", "image/x-targa" };
+
+        /// <summary>
+        /// The list of file extensions that equate to a targa file.
+        /// </summary>
+        public static readonly IEnumerable<string> FileExtensions = new[] { "tga", "vda", "icb", "vst" };
+
+        /// <summary>
+        /// The file header length of a tga image in bytes.
+        /// </summary>
+        public const int FileHeaderLength = 18;
+    }
+}

src/ImageSharp/Formats/Tga/TgaDecoder.cs

@@ -0,0 +1,34 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.IO;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Tga
+{
+    /// <summary>
+    /// Image decoder for Truevision TGA images.
+    /// </summary>
+    public sealed class TgaDecoder : IImageDecoder, ITgaDecoderOptions, IImageInfoDetector
+    {
+        /// <inheritdoc/>
+        public Image<TPixel> Decode<TPixel>(Configuration configuration, Stream stream)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            Guard.NotNull(stream, nameof(stream));
+
+            return new TgaDecoderCore(configuration, this).Decode<TPixel>(stream);
+        }
+
+        /// <inheritdoc />
+        public Image Decode(Configuration configuration, Stream stream) => this.Decode<Rgba32>(configuration, stream);
+
+        /// <inheritdoc/>
+        public IImageInfo Identify(Configuration configuration, Stream stream)
+        {
+            Guard.NotNull(stream, nameof(stream));
+
+            return new TgaDecoderCore(configuration, this).Identify(stream);
+        }
+    }
+}