private async static Task WriteHeaderChunk(PngHeader header)
{
var chunkData = new byte[13];
WriteInteger(chunkData, 0, header.Width);
WriteInteger(chunkData, 4, header.Height);
chunkData[8] = header.BitDepth;
chunkData[9] = header.ColorType;
chunkData[10] = header.CompressionMethod;
chunkData[11] = header.FilterMethod;
chunkData[12] = header.InterlaceMethod;
await WriteChunk(PngChunkTypes.Header, chunkData);
}
/// <summary>
/// Write and PNG file out to a file stream. Currently compression is not supported.
/// </summary>
/// <param name="image">The WriteableBitmap to work on.</param>
/// <param name="stream">The destination file stream.</param>
/// <param name="compression">Level of compression to use (-1=auto, 0=none, 1-100 is percentage).</param>
public async static Task WritePNG(WriteableBitmap image, System.IO.Stream stream, int compression)
{
// Set the global class variables for the image and stream.
_image = image;
_stream = stream;
// Write the png header.
stream.Write(
new byte[]
{
0x89, 0x50, 0x4E, 0x47,
0x0D, 0x0A, 0x1A, 0x0A
}, 0, 8);
// Set the PNG header values for this image.
var header = new PngHeader
{
Width = image.PixelWidth,
Height = image.PixelHeight,
ColorType = 6,
BitDepth = 8,
FilterMethod = 0,
CompressionMethod = 0,
InterlaceMethod = 0
};
// Write out the header.
await WriteHeaderChunk(header);
// Write out the rest of the mandatory fields to the PNG.
await WritePhysicsChunk();
await WriteGammaChunk();
// Currently only uncompressed PNG's are supported, so this if statement really doesn't do anything ;).
if (compression == -1)
{
// Autodetect compression setting
await WriteDataChunksUncompressed();
}
else if (compression == 0)
{
// Write PNG without any compression
await WriteDataChunksUncompressed();
}
else
{
// Write the PNG with a desired compression level
await WriteDataChunks(compression);
}
// Write out the end of the PNG.
await WriteEndChunk();
// Flush the stream to make sure it's all written.
await stream.FlushAsync();
}