gifdecoder.cs

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using System;
using System.Collections;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

namespace LanMsg.Gif.Components
{
	public class GifDecoder 
	{

		/**
		 * File read status: No errors.
		 */
		public static readonly int STATUS_OK = 0;

		/**
		 * File read status: Error decoding file (may be partially decoded)
		 */
		public static readonly int STATUS_FORMAT_ERROR = 1;

		/**
		 * File read status: Unable to open source.
		 */
		public static readonly int STATUS_OPEN_ERROR = 2;

		protected Stream inStream;
		protected int status;

		protected int width; // full image width
		protected int height; // full image height
		protected bool gctFlag; // global color table used
		protected int gctSize; // size of global color table
		protected int loopCount = 1; // iterations; 0 = repeat forever

		protected int[] gct; // global color table
		protected int[] lct; // local color table
		protected int[] act; // active color table

		protected int bgIndex; // background color index
		protected int bgColor; // background color
		protected int lastBgColor; // previous bg color
		protected int pixelAspect; // pixel aspect ratio

		protected bool lctFlag; // local color table flag
		protected bool interlace; // interlace flag
		protected int lctSize; // local color table size

		protected int ix, iy, iw, ih; // current image rectangle
		protected Rectangle lastRect; // last image rect
		protected Image image; // current frame
		protected Bitmap bitmap;
		protected Image lastImage; // previous frame

		protected byte[] block = new byte[256]; // current data block
		protected int blockSize = 0; // block size

		// last graphic control extension info
		protected int dispose = 0;
		// 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
		protected int lastDispose = 0;
		protected bool transparency = false; // use transparent color
		protected int delay = 0; // delay in milliseconds
		protected int transIndex; // transparent color index

		protected static readonly int MaxStackSize = 4096;
		// max decoder pixel stack size

		// LZW decoder working arrays
		protected short[] prefix;
		protected byte[] suffix;
		protected byte[] pixelStack;
		protected byte[] pixels;

		protected ArrayList frames; // frames read from current file
		protected int frameCount;

		public class GifFrame 
		{
			public GifFrame( Image im, int del) 
			{
				image = im;
				delay = del;
			}
			public Image image;
			public int delay;
		}

		 
		/**
		 * Gets display duration for specified frame.
		 *
		 * @param n int index of frame
		 * @return delay in milliseconds
		 */
		public int GetDelay(int n) 
		{
			//
			delay = -1;
			if ((n >= 0) && (n < frameCount)) 
			{
				delay = ((GifFrame) frames[n]).delay;
			}
			return delay;
		}

		/**
		 * Gets the number of frames read from file.
		 * @return frame count
		 */
		public int GetFrameCount() 
		{
			return frameCount;
		}

		/**
		 * Gets the first (or only) image read.
		 *
		 * @return BufferedImage containing first frame, or null if none.
		 */
		public Image GetImage() 
		{
			return GetFrame(0);
		}

		/**
		 * Gets the "Netscape" iteration count, if any.
		 * A count of 0 means repeat indefinitiely.
		 *
		 * @return iteration count if one was specified, else 1.
		 */
		public int GetLoopCount() 
		{
			return loopCount;
		}

		/**
		 * Creates new frame image from current data (and previous
		 * frames as specified by their disposition codes).
		 */
		int [] GetPixels( Bitmap bitmap )
		{
			int [] pixels = new int [ 3 * image.Width * image.Height ];
			int count = 0;
			for (int th = 0; th < image.Height; th++)
			{
				for (int tw = 0; tw < image.Width; tw++)
				{
					Color color = bitmap.GetPixel(tw, th);
					pixels[count] = color.R;
					count++;
					pixels[count] = color.G;
					count++;
					pixels[count] = color.B;
					count++;
				}
			}
			return pixels;
		}

		void SetPixels( int [] pixels )
		{
			int count = 0;
			for (int th = 0; th < image.Height; th++)
			{
				for (int tw = 0; tw < image.Width; tw++)
				{
					Color color = Color.FromArgb( pixels[count++] );
					bitmap.SetPixel( tw, th, color );
				}
			}
		}

		protected void SetPixels() 
		{
			// expose destination image's pixels as int array
			//		int[] dest =
			//			(( int ) image.getRaster().getDataBuffer()).getData();
			int[] dest = GetPixels( bitmap );

			// fill in starting image contents based on last image's dispose code
			if (lastDispose > 0) 
			{
				if (lastDispose == 3) 
				{
					// use image before last
					int n = frameCount - 2;
					if (n > 0) 
					{
						lastImage = GetFrame(n - 1);
					} 
					else 
					{
						lastImage = null;
					}
				}

				if (lastImage != null) 
				{
					//				int[] prev =
					//					((DataBufferInt) lastImage.getRaster().getDataBuffer()).getData();
					int[] prev = GetPixels( new Bitmap( lastImage ) );
					Array.Copy(prev, 0, dest, 0, width * height);
					// copy pixels

					if (lastDispose == 2) 
					{
						// fill last image rect area with background color
						Graphics g = Graphics.FromImage( image );
						Color c = Color.Empty;
						if (transparency) 
						{
							c = Color.FromArgb( 0, 0, 0, 0 ); 	// assume background is transparent
						} 
						else 
						{
							c = Color.FromArgb( lastBgColor ) ;
							//						c = new Color(lastBgColor); // use given background color
						}
						Brush brush = new SolidBrush( c );
						g.FillRectangle( brush, lastRect );
						brush.Dispose();
						g.Dispose();
					}
				}
			}

			// copy each source line to the appropriate place in the destination
			int pass = 1;
			int inc = 8;
			int iline = 0;
			for (int i = 0; i < ih; i++) 
			{
				int line = i;
				if (interlace) 
				{
					if (iline >= ih) 
					{
						pass++;
						switch (pass) 
						{
							case 2 :
								iline = 4;
								break;
							case 3 :
								iline = 2;
								inc = 4;
								break;
							case 4 :
								iline = 1;
								inc = 2;
								break;
						}
					}
					line = iline;
					iline += inc;
				}
				line += iy;
				if (line < height) 
				{
					int k = line * width;
					int dx = k + ix; // start of line in dest
					int dlim = dx + iw; // end of dest line
					if ((k + width) < dlim) 
					{
						dlim = k + width; // past dest edge
					}
					int sx = i * iw; // start of line in source
					while (dx < dlim) 
					{
						// map color and insert in destination
						int index = ((int) pixels[sx++]) & 0xff;
						int c = act[index];
						if (c != 0) 
						{
							dest[dx] = c;
						}
						dx++;
					}
				}
			}
			SetPixels( dest );
		}

		/**
		 * Gets the image contents of frame n.
		 *
		 * @return BufferedImage representation of frame, or null if n is invalid.
		 */
		public Image GetFrame(int n) 
		{
			Image im = null;
			if ((n >= 0) && (n < frameCount)) 
			{
				im = ((GifFrame) frames[n] ).image;
			}
			return im;
		}

		/**
		 * Gets image size.
		 *
		 * @return GIF image dimensions
		 */
		public Size GetFrameSize() 
		{
			return new Size(width, height);
		}

		/**
		 * Reads GIF image from stream
		 *
		 * @param BufferedInputStream containing GIF file.
		 * @return read status code (0 = no errors)
		 */
		public int Read( Stream inStream ) 
		{
			Init();
			if ( inStream != null) 
			{
				this.inStream = inStream;
				ReadHeader();
				if (!Error()) 
				{
					ReadContents();
					if (frameCount < 0) 
					{
						status = STATUS_FORMAT_ERROR;
					}
				}
				inStream.Close();
			} 
			else 
			{
				status = STATUS_OPEN_ERROR;
			}
			return status;
		}

		/**
		 * Reads GIF file from specified file/URL source  
		 * (URL assumed if name contains ":/" or "file:")
		 *
		 * @param name String containing source
		 * @return read status code (0 = no errors)
		 */
		public int Read(String name) 
		{
			status = STATUS_OK;
			try 
			{
				name = name.Trim().ToLower();
				status = Read( new FileInfo( name ).OpenRead() );
			} 
			catch (IOException e) 
			{
				status = STATUS_OPEN_ERROR;
			}

			return status;
		}

		/**
		 * Decodes LZW image data into pixel array.
		 * Adapted from John Cristy's ImageMagick.
		 */
		protected void DecodeImageData() 
		{
			int NullCode = -1;
			int npix = iw * ih;
			int available, 
				clear,
				code_mask,
				code_size,
				end_of_information,
				in_code,
				old_code,
				bits,
				code,
				count,
				i,
				datum,
				data_size,
				first,
				top,
				bi,
				pi;

			if ((pixels == null) || (pixels.Length < npix)) 
			{
				pixels = new byte[npix]; // allocate new pixel array
			}
			if (prefix == null) prefix = new short[MaxStackSize];
			if (suffix == null) suffix = new byte[MaxStackSize];
			if (pixelStack == null) pixelStack = new byte[MaxStackSize + 1];

			//  Initialize GIF data stream decoder.

			data_size = Read();
			clear = 1 << data_size;
			end_of_information = clear + 1;
			available = clear + 2;
			old_code = NullCode;
			code_size = data_size + 1;
			code_mask = (1 << code_size) - 1;
			for (code = 0; code < clear; code++) 
			{
				prefix[code] = 0;
				suffix[code] = (byte) code;
			}

			//  Decode GIF pixel stream.

			datum = bits = count = first = top = pi = bi = 0;

			for (i = 0; i < npix;) 
			{
				if (top == 0) 
				{
					if (bits < code_size) 
					{
						//  Load bytes until there are enough bits for a code.
						if (count == 0) 
						{
							// Read a new data block.
							count = ReadBlock();
							if (count <= 0)
								break;
							bi = 0;
						}
						datum += (((int) block[bi]) & 0xff) << bits;