/// <summary>
/// Losslessly transform the JPEG image associated with this transformer instance into one or more JPEG images
/// stored in the given destination buffers. Lossless transforms work by moving the raw coefficients from one
/// JPEG image structure to another without altering the values of the coefficients. While this is typically
/// faster than decompressing the image, transforming it, and re-compressing it, lossless transforms are not
/// free. Each lossless transform requires reading and performing Huffman decoding on all of the coefficients
/// in the source image, regardless of the size of the destination image, thus this method provides a means of
/// generating multiple transformed images from the same source or of applying multiple transformations
/// simultaneously, in order to eliminate the need to read the source coefficients multiple times.
/// </summary>
/// <param name="destBuffers">
/// An array of image buffers. <paramref name="destBuffers" />[i] will receive a JPEG image that has been
/// transformed using the parameters in <paramref name="transforms" />[i]. Use
/// <see cref="NativeMethods.bufSize" /> to determine the maximum size for each buffer based on the
/// transformed or cropped width and height and the chroma subsampling used in the source image.
/// </param>
/// <param name="transforms">An array of <seealso cref="TurboJpegTransform" /> instances, each of which
/// specifies the transform parameters and/or cropping region for the corresponding transformed output image.
/// </param>
/// <param name="options">The flags to use for the transforms.</param>
public void Transform(byte[][] destBuffers, TurboJpegTransform[] transforms, TurboJpegFlags options)
{
Contract.Requires(destBuffers != null);
Contract.Requires(transforms != null);
Contract.Requires(transforms.Length == destBuffers.Length);
Contract.Requires(Enum.IsDefined(typeof(TransformOptions), options));
Contract.Ensures(Contract.ForAll(destBuffers, _ => _ != null));
Contract.Assume(this.JpegBuffer != null, "JPEG buffer not initialized");
var count = destBuffers.Length;
var destBufferPtrs = new IntPtr[count];
this.transformedSizes = new int[count];
if (NativeMethods.transform(this.Handle,
this.JpegBuffer,
this.JpegSize,
count,
ref destBufferPtrs,
ref this.transformedSizes,
transforms,
options) != 0)
{
throw new Exception(TurboJpegInterop.GetLastError());
}
// we now have the result in buffers on the unmanaged heap
for (var i = 0; i < count; ++i)
{
destBuffers[i] = new byte[this.transformedSizes[i]];
Marshal.Copy(destBufferPtrs[i], destBuffers[i], 0, this.transformedSizes[i]);
}
}
/// <summary>
/// Losslessly transform the JPEG image associated with this transformer instance and return an array of
/// <seealso cref="TurboJpegDecompressor" /> instances, each of which has a transformed JPEG image associated
/// with it.
/// </summary>
/// <param name="transforms">An array of <see cref="TurboJpegTransform" /> instances, each of which specifies
/// the transform parameters and/or cropping region for the corresponding transformed output image.</param>
/// <param name="flags">The flags to use when transforming.</param>
/// <param name="preallocateBuffers">If set to <c>true</c>, preallocate buffers.</param>
/// <returns>
/// An array of <seealso cref="TurboJpegDecompressor" /> instances, each of which has a transformed
/// JPEG image associated with it.
/// </returns>
public TurboJpegDecompressor[] Transform(TurboJpegTransform[] transforms, TurboJpegFlags flags, bool preallocateBuffers)
{
Contract.Requires(transforms != null);
Contract.Requires(Enum.IsDefined(typeof(TransformOptions), flags));
Contract.Ensures(Contract.Result<TurboJpegDecompressor[]>() != null);
Contract.Ensures(Contract.Result<TurboJpegDecompressor[]>().Length == transforms.Length);
Contract.Ensures(Contract.ForAll(Contract.Result<TurboJpegDecompressor[]>(), _ => _ != null));
var count = transforms.Length;
var destinationBuffers = new byte[count][];
Contract.Assume(this.Width > 0, "JPEG buffer not initialized");
Contract.Assume(this.Height > 0, "JPEG buffer not initialized");
var decompressors = new TurboJpegDecompressor[count];
if (preallocateBuffers)
{
for (var i = 0; i < count; i++)
{
var width = this.Width;
var height = this.Height;
if ((transforms[i].Options & TransformOptions.Crop) != 0)
{
if (transforms[i].Width != 0)
{
width = transforms[i].Width;
}
if (transforms[i].Height != 0)
{
height = transforms[i].Height;
}
}
destinationBuffers[i] = new byte[NativeMethods.bufSize(width, height, this.Subsampling)];
}
this.Transform(destinationBuffers, transforms, flags);
for (var i = 0; i < count; i++)
{
decompressors[i] = new TurboJpegDecompressor(destinationBuffers[i]);
}
}
else
{
var destBufferPtrs = new IntPtr[count];
this.transformedSizes = new int[count];
if (NativeMethods.transform(this.Handle,
this.JpegBuffer,
this.JpegSize,
count,
ref destBufferPtrs,
ref this.transformedSizes,
transforms,
flags) != 0)
{
throw new Exception(TurboJpegInterop.GetLastError());
}
// we now have the result in buffers on the unmanaged heap
for (var i = 0; i < count; ++i)
{
decompressors[i] = new TurboJpegDecompressor();
decompressors[i].SetJpegImage(destBufferPtrs[i]);
}
}
return decompressors;
}
internal static extern int transform(IntPtr handle,
byte[] sourceBuffer,
int sourceSize,
int count,
ref IntPtr[] destinationBuffers,
ref int[] sizes,
TurboJpegTransform[] transforms,
[MarshalAs(UnmanagedType.I4)] TurboJpegFlags flags);