/// <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);
}
/// <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;
// Bit at position 5 of the descriptor indicates, that the origin is top left instead of bottom right.
if ((this.fileHeader.ImageDescriptor & (1 << 5)) != 0)
{
return(true);
}
return(false);
}