PureCSharpPNGWriterProgram.cs

using System;
using System.IO;
using System.IO.Compression;
using System.Collections.Generic;
using System.Linq;
using System.Xml;
using System.Text;

namespace PureCSharpPngWriter
{
	public static class PureCSharpPngWriterProgram
	{
		private static uint Adler32(byte[] bytes) {
			const uint a32mod = 65521;
			uint s1 = 1, s2 = 0;
			foreach (byte b in bytes) {
				s1 = (s1 + b) % a32mod;
				s2 = (s2 + s1) % a32mod;
			}
			return ((s2 << 16) + s1);
		}
		private static uint[] crc32_tab = {
			0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c, 
			0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
		};
		private static uint UpdateCRC32(byte[] buf, uint old_crc) {
			uint crc = old_crc;

			for (int n = 0; n < buf.Length; n += 1) { 
				crc ^= buf[n];
				crc = (crc >> 4) ^ crc32_tab[crc & 15];
				crc = (crc >> 4) ^ crc32_tab[crc & 15];
			}

			return crc;
		}
		private static void PutUInt32BE(byte[] buf, uint offset, uint val) {
			buf[offset + 0] = (byte)((val & 0xFF000000) >> 24);
			buf[offset + 1] = (byte)((val & 0x00FF0000) >> 16);
			buf[offset + 2] = (byte)((val & 0x0000FF00) >> 8);
			buf[offset + 3] = (byte)((val & 0x000000FF) >> 0);
		}
		private static void WritePNGChunk(Stream f, byte[] identBuf, byte[] buf) {
			byte[] size = new byte[4];
			PutUInt32BE(size, 0, (uint)buf.Length);
			byte[] crcBuf = new byte[4];
			uint crc = 0xFFFFFFFF;
			crc = UpdateCRC32(identBuf, crc);
			crc = UpdateCRC32(buf, crc);
			crc ^= 0xFFFFFFFF;
			PutUInt32BE(crcBuf, 0, crc);
			f.Write(size, 0, size.Length);
			f.Write(identBuf, 0, identBuf.Length);
			f.Write(buf, 0, buf.Length);
			f.Write(crcBuf, 0, crcBuf.Length);
		}
		private static byte[] UInt32LEArrayToByteArray(uint[] inbuf) {
			byte[] outbuf = new byte[inbuf.Length * 4];
			for (var i = 0; i < inbuf.Length; i += 1) {
				uint val = inbuf[i];
				outbuf[(i * 4) + 3] = (byte)((val & 0xFF000000) >> 24);
				outbuf[(i * 4) + 2] = (byte)((val & 0x00FF0000) >> 16);
				outbuf[(i * 4) + 1] = (byte)((val & 0x0000FF00) >> 8);
				outbuf[(i * 4) + 0] = (byte)((val & 0x000000FF) >> 0);
			}
			return outbuf;
		}
		static void Main(string[] args)
		{
			byte[] pngHeader = new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0d, 0x0a, 0x1a, 0x0a };
			byte[] pngIHDR = new byte[13];
			byte[] pngIDAT = new byte[0];
			byte[] pngIEND = new byte[0];
			byte[] pngChunkIdIHDR = new byte[] { 0x49, 0x48, 0x44, 0x52 };
			byte[] pngChunkIdIDAT = new byte[] { 0x49, 0x44, 0x41, 0x54 };
			byte[] pngChunkIdIEND = new byte[] { 0x49, 0x45, 0x4E, 0x44 };

			uint[] pixels = new uint[256 * 256];

			for (var i = 0; i < pixels.Length; i += 1)
			{
				pixels[i] = (((uint)0 & 0xFF) << 0) | (((uint)0 & 0xFF) << 8) | (((uint)0xFF & 0xFF) << 16) | (((uint)0xFF & 0xFF) << 24);
			}

			byte[] pixelsBytes = UInt32LEArrayToByteArray(pixels);

			int imageWidth = 256;
			int imageHeight = 256;

			PutUInt32BE(pngIHDR, 0, (uint)imageWidth); // width
			PutUInt32BE(pngIHDR, 4, (uint)imageHeight); // height
			pngIHDR[8] = 8; // depth
			pngIHDR[9] = 6; // color type
			pngIHDR[10] = 0; // compression
			pngIHDR[11] = 0; // filter
			pngIHDR[12] = 0; // interlace

			using (var cbio = new MemoryStream(pixelsBytes.Length)) {
				cbio.WriteByte(0x78);
				cbio.WriteByte(0x9C);
				using (var cbio2 = new MemoryStream(pixelsBytes.Length + imageHeight)) {
					for (int row = 0; row < imageHeight; row += 1) {
						cbio2.WriteByte(0x00);
						cbio2.Write(pixelsBytes, ((imageHeight - (row + 1)) * imageWidth) * 4, imageWidth * 4);
					}
					cbio2.Seek(0, SeekOrigin.Begin);
					byte[] filteredPixelsBytes = new byte[cbio2.Length];
					cbio2.Read(filteredPixelsBytes, 0, (int)cbio2.Length);
					using (var cbiod = new DeflateStream(cbio, CompressionMode.Compress, true)) {
						cbiod.Write(filteredPixelsBytes, 0, filteredPixelsBytes.Length);
					}
					byte[] adlerBuf = new byte[4];
					PutUInt32BE(adlerBuf, 0, Adler32(filteredPixelsBytes));
					cbio.Write(adlerBuf, 0, adlerBuf.Length);
				}
				cbio.Seek(0, SeekOrigin.Begin);
				pngIDAT = new byte[cbio.Length];
				cbio.Read(pngIDAT, 0, (int)cbio.Length);
			}

			using (var wf = File.Open("outfile.png", FileMode.Create)) {
				wf.Write(pngHeader, 0, pngHeader.Length);
				WritePNGChunk(wf, pngChunkIdIHDR, pngIHDR);
				WritePNGChunk(wf, pngChunkIdIDAT, pngIDAT);
				WritePNGChunk(wf, pngChunkIdIEND, pngIEND);
			}
		}
	}
}