/// <summary>
/// Reads the tga file header from the stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
/// <returns>The image origin.</returns>
private TgaImageOrigin ReadFileHeader(Stream stream)
{
this.currentStream = stream;
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
this.currentStream.Read(buffer, 0, TgaFileHeader.Size);
this.fileHeader = TgaFileHeader.Parse(buffer);
this.metadata = new ImageMetadata();
this.tgaMetadata = this.metadata.GetTgaMetadata();
this.tgaMetadata.BitsPerPixel = (TgaBitsPerPixel)this.fileHeader.PixelDepth;
var alphaBits = this.fileHeader.ImageDescriptor & 0xf;
if (alphaBits != 0 && alphaBits != 1 && alphaBits != 8)
{
TgaThrowHelper.ThrowImageFormatException("Invalid alpha channel bits");
}
this.tgaMetadata.AlphaChannelBits = (byte)alphaBits;
this.hasAlpha = alphaBits > 0;
// Bits 4 and 5 describe the image origin.
var origin = (TgaImageOrigin)((this.fileHeader.ImageDescriptor & 0x30) >> 4);
return(origin);
}
/// <summary>
/// Reads the tga file header from the stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
/// <returns>true, if the image origin is top left.</returns>
private bool ReadFileHeader(Stream stream)
{
this.currentStream = stream;
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
this.currentStream.Read(buffer, 0, TgaFileHeader.Size);
this.fileHeader = TgaFileHeader.Parse(buffer);
this.metadata = new ImageMetadata();
this.tgaMetadata = this.metadata.GetTgaMetadata();
this.tgaMetadata.BitsPerPixel = (TgaBitsPerPixel)this.fileHeader.PixelDepth;
var alphaBits = this.fileHeader.ImageDescriptor & 0xf;
if (alphaBits != 0 && alphaBits != 1 && alphaBits != 8)
{
TgaThrowHelper.ThrowImageFormatException("Invalid alpha channel bits");
}
this.tgaMetadata.AlphaChannelBits = (byte)alphaBits;
this.hasAlpha = alphaBits > 0;
// TODO: bits 4 and 5 describe the image origin. See spec page 9. bit 4 is currently ignored.
// Theoretically the origin could also be top right and bottom right.
// Bit at position 5 of the descriptor indicates, that the origin is top left instead of bottom left.
if ((this.fileHeader.ImageDescriptor & (1 << 5)) != 0)
{
return(true);
}
return(false);
}
/// <inheritdoc/>
public Image <TPixel> Decode <TPixel>(Configuration configuration, Stream stream)
where TPixel : unmanaged, IPixel <TPixel>
{
Guard.NotNull(stream, nameof(stream));
var decoder = new TgaDecoderCore(configuration, this);
try
{
return(decoder.Decode <TPixel>(stream));
}
catch (InvalidMemoryOperationException ex)
{
Size dims = decoder.Dimensions;
TgaThrowHelper.ThrowInvalidImageContentException($"Can not decode image. Failed to allocate buffers for possibly degenerate dimensions: {dims.Width}x{dims.Height}.", ex);
// Not reachable, as the previous statement will throw a exception.
return(null);
}
}
/// <summary>
/// Decodes the image from the specified stream.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="stream">The stream, where the image should be decoded from. Cannot be null.</param>
/// <exception cref="System.ArgumentNullException">
/// <para><paramref name="stream"/> is null.</para>
/// </exception>
/// <returns>The decoded image.</returns>
public Image <TPixel> Decode <TPixel>(Stream stream)
where TPixel : unmanaged, IPixel <TPixel>
{
try
{
TgaImageOrigin origin = this.ReadFileHeader(stream);
this.currentStream.Skip(this.fileHeader.IdLength);
// Parse the color map, if present.
if (this.fileHeader.ColorMapType != 0 && this.fileHeader.ColorMapType != 1)
{
TgaThrowHelper.ThrowNotSupportedException($"Unknown tga colormap type {this.fileHeader.ColorMapType} found");
}
if (this.fileHeader.Width == 0 || this.fileHeader.Height == 0)
{
throw new UnknownImageFormatException("Width or height cannot be 0");
}
var image = Image.CreateUninitialized <TPixel>(this.configuration, this.fileHeader.Width, this.fileHeader.Height, this.metadata);
Buffer2D <TPixel> pixels = image.GetRootFramePixelBuffer();
if (this.fileHeader.ColorMapType == 1)
{
if (this.fileHeader.CMapLength <= 0)
{
TgaThrowHelper.ThrowImageFormatException("Missing tga color map length");
}
if (this.fileHeader.CMapDepth <= 0)
{
TgaThrowHelper.ThrowImageFormatException("Missing tga color map depth");
}
int colorMapPixelSizeInBytes = this.fileHeader.CMapDepth / 8;
int colorMapSizeInBytes = this.fileHeader.CMapLength * colorMapPixelSizeInBytes;
using (IManagedByteBuffer palette = this.memoryAllocator.AllocateManagedByteBuffer(colorMapSizeInBytes, AllocationOptions.Clean))
{
this.currentStream.Read(palette.Array, this.fileHeader.CMapStart, colorMapSizeInBytes);
if (this.fileHeader.ImageType == TgaImageType.RleColorMapped)
{
this.ReadPalettedRle(
this.fileHeader.Width,
this.fileHeader.Height,
pixels,
palette.Array,
colorMapPixelSizeInBytes,
origin);
}
else
{
this.ReadPaletted(
this.fileHeader.Width,
this.fileHeader.Height,
pixels,
palette.Array,
colorMapPixelSizeInBytes,
origin);
}
}
return(image);
}
// Even if the image type indicates it is not a paletted image, it can still contain a palette. Skip those bytes.
if (this.fileHeader.CMapLength > 0)
{
int colorMapPixelSizeInBytes = this.fileHeader.CMapDepth / 8;
this.currentStream.Skip(this.fileHeader.CMapLength * colorMapPixelSizeInBytes);
}
switch (this.fileHeader.PixelDepth)
{
case 8:
if (this.fileHeader.ImageType.IsRunLengthEncoded())
{
this.ReadRle(this.fileHeader.Width, this.fileHeader.Height, pixels, 1, origin);
}
else
{
this.ReadMonoChrome(this.fileHeader.Width, this.fileHeader.Height, pixels, origin);
}
break;
case 15:
case 16:
if (this.fileHeader.ImageType.IsRunLengthEncoded())
{
this.ReadRle(this.fileHeader.Width, this.fileHeader.Height, pixels, 2, origin);
}
else
{
this.ReadBgra16(this.fileHeader.Width, this.fileHeader.Height, pixels, origin);
}
break;
case 24:
if (this.fileHeader.ImageType.IsRunLengthEncoded())
{
this.ReadRle(this.fileHeader.Width, this.fileHeader.Height, pixels, 3, origin);
}
else
{
this.ReadBgr24(this.fileHeader.Width, this.fileHeader.Height, pixels, origin);
}
break;
case 32:
if (this.fileHeader.ImageType.IsRunLengthEncoded())
{
this.ReadRle(this.fileHeader.Width, this.fileHeader.Height, pixels, 4, origin);
}
else
{
this.ReadBgra32(this.fileHeader.Width, this.fileHeader.Height, pixels, origin);
}
break;
default:
TgaThrowHelper.ThrowNotSupportedException("ImageSharp does not support this kind of tga files.");
break;
}
return(image);
}
catch (IndexOutOfRangeException e)
{
throw new ImageFormatException("TGA image does not have a valid format.", e);
}
}