GifEncoder.java

// GifEncoder - write out an image as a GIF
//
// Transparency handling and variable bit size courtesy of Jack Palevich.
//
// Copyright (C)1996,1998 by Jef Poskanzer <jef@acme.com>. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package org.egonet.util;

import java.awt.Image;
import java.awt.image.ImageProducer;
import java.io.IOException;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.Map;

/// Write out an image as a GIF.
// <P>
// <A HREF="/resources/classes/Acme/JPM/Encoders/GifEncoder.java">Fetch the
// software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>
// <P>
// @see ToGif

public class GifEncoder extends ImageEncoder {

	private boolean interlace = false;

	/// Constructor from Image.
	// @param img The image to encode.
	// @param out The stream to write the GIF to.
	public GifEncoder(Image img, OutputStream out) throws IOException {
		super(img, out);
	}

	/// Constructor from Image with interlace setting.
	// @param img The image to encode.
	// @param out The stream to write the GIF to.
	// @param interlace Whether to interlace.
	public GifEncoder(Image img, OutputStream out, boolean interlace) throws IOException {
		super(img, out);
		this.interlace = interlace;
	}

	/// Constructor from ImageProducer.
	// @param prod The ImageProducer to encode.
	// @param out The stream to write the GIF to.
	public GifEncoder(ImageProducer prod, OutputStream out) throws IOException {
		super(prod, out);
	}

	/// Constructor from ImageProducer with interlace setting.
	// @param prod The ImageProducer to encode.
	// @param out The stream to write the GIF to.
	public GifEncoder(ImageProducer prod, OutputStream out, boolean interlace) throws IOException {
		super(prod, out);
		this.interlace = interlace;
	}

	int width, height;
	int[][] rgbPixels;

	void encodeStart(int width, int height) throws IOException {
		this.width = width;
		this.height = height;
		rgbPixels = new int[height][width];
	}

	void encodePixels(int x, int y, int w, int h, int[] rgbPixels, int off, int scansize) throws IOException {
		// Save the pixels.
		for (int row = 0; row < h; ++row)
			System.arraycopy(rgbPixels, row * scansize + off, this.rgbPixels[y + row], x, w);

	}

	Map<Integer,GifEncoderHashitem> colorHash;

	void encodeDone() throws IOException {
		int transparentIndex = -1;
		int transparentRgb = -1;
		// Put all the pixels into a hash table.
		colorHash = new HashMap<Integer,GifEncoderHashitem>();
		int index = 0;
		for (int row = 0; row < height; ++row) {
			//int rowOffset = row * width;
			for (int col = 0; col < width; ++col) {
				int rgb = rgbPixels[row][col];
				boolean isTransparent = ((rgb >>> 24) < 0x80);
				if (isTransparent) {
					if (transparentIndex < 0) {
						// First transparent color; remember it.
						transparentIndex = index;
						transparentRgb = rgb;
					} else if (rgb != transparentRgb) {
						// A second transparent color; replace it with
						// the first one.
						rgbPixels[row][col] = rgb = transparentRgb;
					}
				}
				GifEncoderHashitem item = (GifEncoderHashitem) colorHash.get(rgb);
				if (item == null) {
					if (index >= 256)
						throw new IOException("too many colors for a GIF: " + index);
					item = new GifEncoderHashitem(rgb, 1, index, isTransparent);
					++index;
					colorHash.put(rgb, item);
				} else
					++item.count;
			}
		}

		// Figure out how many bits to use.
		int logColors;
		if (index <= 2)
			logColors = 1;
		else if (index <= 4)
			logColors = 2;
		else if (index <= 16)
			logColors = 4;
		else
			logColors = 8;

		// Turn colors into colormap entries.
		int mapSize = 1 << logColors;
		byte[] reds = new byte[mapSize];
		byte[] grns = new byte[mapSize];
		byte[] blus = new byte[mapSize];
		for (GifEncoderHashitem item : colorHash.values()) {
			reds[item.index] = (byte) ((item.rgb >> 16) & 0xff);
			grns[item.index] = (byte) ((item.rgb >> 8) & 0xff);
			blus[item.index] = (byte) (item.rgb & 0xff);
		}

		GIFEncode(out, width, height, interlace, (byte) 0, transparentIndex, logColors, reds, grns, blus);
	}

	byte GetPixel(int x, int y) throws IOException {
		GifEncoderHashitem item = (GifEncoderHashitem) colorHash.get(rgbPixels[y][x]);
		if (item == null)
			throw new IOException("color not found");
		return (byte) item.index;
	}

	static void writeString(OutputStream out, String str) throws IOException {
		byte[] buf = str.getBytes();
		out.write(buf);
	}

	// Adapted from ppmtogif, which is based on GIFENCOD by David
	// Rowley <mgardi@watdscu.waterloo.edu>. Lempel-Zim compression
	// based on "compress".

	int Width, Height;
	boolean Interlace;
	int curx, cury;
	int CountDown;
	int Pass = 0;

	void GIFEncode(
		OutputStream outs,
		int Width,
		int Height,
		boolean Interlace,
		byte Background,
		int Transparent,
		int BitsPerPixel,
		byte[] Red,
		byte[] Green,
		byte[] Blue)
		throws IOException {
		byte B;
		int LeftOfs, TopOfs;
		int ColorMapSize;
		int InitCodeSize;
		int i;

		this.Width = Width;
		this.Height = Height;
		this.Interlace = Interlace;
		ColorMapSize = 1 << BitsPerPixel;
		LeftOfs = TopOfs = 0;

		// Calculate number of bits we are expecting
		CountDown = Width * Height;

		// Indicate which pass we are on (if interlace)
		Pass = 0;

		// The initial code size
		if (BitsPerPixel <= 1)
			InitCodeSize = 2;
		else
			InitCodeSize = BitsPerPixel;

		// Set up the current x and y position
		curx = 0;
		cury = 0;

		// Write the Magic header
		writeString(outs, "GIF89a");

		// Write out the screen width and height
		Putword(Width, outs);
		Putword(Height, outs);

		// Indicate that there is a global colour map
		B = (byte) 0x80; // Yes, there is a color map
		// OR in the resolution
		B |= (byte) ((8 - 1) << 4);
		// Not sorted
		// OR in the Bits per Pixel
		B |= (byte) ((BitsPerPixel - 1));

		// Write it out
		Putbyte(B, outs);

		// Write out the Background colour
		Putbyte(Background, outs);

		// Pixel aspect ratio - 1:1.
		//Putbyte( (byte) 49, outs );
		// Java's GIF reader currently has a bug, if the aspect ratio byte is
		// not zero it throws an ImageFormatException. It doesn't know that
		// 49 means a 1:1 aspect ratio. Well, whatever, zero works with all
		// the other decoders I've tried so it probably doesn't hurt.
		Putbyte((byte) 0, outs);

		// Write out the Global Colour Map
		for (i = 0; i < ColorMapSize; ++i) {
			Putbyte(Red[i], outs);
			Putbyte(Green[i], outs);
			Putbyte(Blue[i], outs);
		}

		// Write out extension for transparent colour index, if necessary.
		if (Transparent != -1) {
			Putbyte((byte) '!', outs);
			Putbyte((byte) 0xf9, outs);
			Putbyte((byte) 4, outs);
			Putbyte((byte) 1, outs);
			Putbyte((byte) 0, outs);
			Putbyte((byte) 0, outs);
			Putbyte((byte) Transparent, outs);
			Putbyte((byte) 0, outs);
		}

		// Write an Image separator
		Putbyte((byte) ',', outs);

		// Write the Image header
		Putword(LeftOfs, outs);
		Putword(TopOfs, outs);
		Putword(Width, outs);
		Putword(Height, outs);

		// Write out whether or not the image is interlaced
		if (Interlace)
			Putbyte((byte) 0x40, outs);
		else
			Putbyte((byte) 0x00, outs);

		// Write out the initial code size
		Putbyte((byte) InitCodeSize, outs);

		// Go and actually compress the data
		compress(InitCodeSize + 1, outs);

		// Write out a Zero-length packet (to end the series)
		Putbyte((byte) 0, outs);

		// Write the GIF file terminator
		Putbyte((byte) ';', outs);
	}

	// Bump the 'curx' and 'cury' to point to the next pixel
	void BumpPixel() {
		// Bump the current X position
		++curx;

		// If we are at the end of a scan line, set curx back to the beginning
		// If we are interlaced, bump the cury to the appropriate spot,
		// otherwise, just increment it.
		if (curx == Width) {
			curx = 0;

			if (!Interlace)
				++cury;
			else {
				switch (Pass) {
					case 0 :
						cury += 8;
						if (cury >= Height) {
							++Pass;
							cury = 4;
						}
						break;

					case 1 :
						cury += 8;
						if (cury >= Height) {
							++Pass;
							cury = 2;
						}
						break;

					case 2 :
						cury += 4;
						if (cury >= Height) {
							++Pass;
							cury = 1;
						}
						break;

					case 3 :
						cury += 2;
						break;
				}
			}
		}
	}

	static final int EOF = -1;

	// Return the next pixel from the image
	int GIFNextPixel() throws IOException {
		byte r;

		if (CountDown == 0)
			return EOF;

		--CountDown;

		r = GetPixel(curx, cury);

		BumpPixel();

		return r & 0xff;
	}

	// Write out a word to the GIF file
	void Putword(int w, OutputStream outs) throws IOException {
		Putbyte((byte) (w & 0xff), outs);
		Putbyte((byte) ((w >> 8) & 0xff), outs);
	}

	// Write out a byte to the GIF file
	void Putbyte(byte b, OutputStream outs) throws IOException {
		outs.write(b);
	}

	// GIFCOMPR.C - GIF Image compression routines
	//
	// Lempel-Ziv compression based on 'compress'. GIF modifications by
	// David Rowley (mgardi@watdcsu.waterloo.edu)

	// General DEFINEs

	static final int BITS = 12;

	static final int HSIZE = 5003; // 80% occupancy

	// GIF Image compression - modified 'compress'
	//
	// Based on: compress.c - File compression ala IEEE Computer, June 1984.
	//
	// By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
	//              Jim McKie (decvax!mcvax!jim)
	//              Steve Davies (decvax!vax135!petsd!peora!srd)
	//              Ken Turkowski (decvax!decwrl!turtlevax!ken)
	//              James A. Woods (decvax!ihnp4!ames!jaw)
	//              Joe Orost (decvax!vax135!petsd!joe)

	int n_bits; // number of bits/code
	int maxbits = BITS; // user settable max # bits/code
	int maxcode; // maximum code, given n_bits
	int maxmaxcode = 1 << BITS; // should NEVER generate this
																// code

	final int MAXCODE(int n_bits) {
		return (1 << n_bits) - 1;
	}

	int[] htab = new int[HSIZE];
	int[] codetab = new int[HSIZE];

	int hsize = HSIZE; // for dynamic table sizing

	int free_ent = 0; // first unused entry

	// block compression parameters -- after all codes are used up,
	// and compression rate changes, start over.
	boolean clear_flg = false;

	// Algorithm: use open addressing double hashing (no chaining) on the
	// prefix code / next character combination. We do a variant of Knuth's
	// algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
	// secondary probe. Here, the modular division first probe is gives way
	// to a faster exclusive-or manipulation. Also do block compression with
	// an adaptive reset, whereby the code table is cleared when the compression
	// ratio decreases, but after the table fills. The variable-length output
	// codes are re-sized at this point, and a special CLEAR code is generated
	// for the decompressor. Late addition: construct the table according to
	// file size for noticeable speed improvement on small files. Please direct
	// questions about this implementation to ames!jaw.

	int g_init_bits;

	int ClearCode;
	int EOFCode;

	void compress(int init_bits, OutputStream outs) throws IOException {
		int fcode;
		int i /* = 0 */;
		int c;
		int ent;
		int disp;
		int hsize_reg;
		int hshift;

		// Set up the globals: g_init_bits - initial number of bits
		g_init_bits = init_bits;

		// Set up the necessary values
		clear_flg = false;
		n_bits = g_init_bits;
		maxcode = MAXCODE(n_bits);

		ClearCode = 1 << (init_bits - 1);
		EOFCode = ClearCode + 1;
		free_ent = ClearCode + 2;

		char_init();

		ent = GIFNextPixel();

		hshift = 0;
		for (fcode = hsize; fcode < 65536; fcode *= 2)
			++hshift;
		hshift = 8 - hshift; // set hash code range bound

		hsize_reg = hsize;
		cl_hash(hsize_reg); // clear hash table

		output(ClearCode, outs);

		outer_loop : while ((c = GIFNextPixel()) != EOF) {
			fcode = (c << maxbits) + ent;
			i = (c << hshift) ^ ent; // xor hashing

			if (htab[i] == fcode) {
				ent = codetab[i];
				continue;
			} else if (htab[i] >= 0) // non-empty slot
				{
				disp = hsize_reg - i; // secondary hash (after G. Knott)
				if (i == 0)
					disp = 1;
				do {
					if ((i -= disp) < 0)
						i += hsize_reg;

					if (htab[i] == fcode) {
						ent = codetab[i];
						continue outer_loop;
					}
				} while (htab[i] >= 0);
			}
			output(ent, outs);
			ent = c;
			if (free_ent < maxmaxcode) {
				codetab[i] = free_ent++; // code -> hashtable
				htab[i] = fcode;
			} else
				cl_block(outs);
		}
		// Put out the final code.
		output(ent, outs);
		output(EOFCode, outs);
	}

	// output
	//
	// Output the given code.
	// Inputs:
	//      code: A n_bits-bit integer. If == -1, then EOF. This assumes
	//              that n_bits =< wordsize - 1.
	// Outputs:
	//      Outputs code to the file.
	// Assumptions:
	//      Chars are 8 bits long.
	// Algorithm:
	//      Maintain a BITS character long buffer (so that 8 codes will
	// fit in it exactly). Use the VAX insv instruction to insert each
	// code in turn. When the buffer fills up empty it and start over.

	int cur_accum = 0;
	int cur_bits = 0;

	int masks[] =
		{
			0x0000,
			0x0001,
			0x0003,
			0x0007,
			0x000F,
			0x001F,
			0x003F,
			0x007F,
			0x00FF,
			0x01FF,
			0x03FF,
			0x07FF,
			0x0FFF,
			0x1FFF,
			0x3FFF,
			0x7FFF,
			0xFFFF };

	void output(int code, OutputStream outs) throws IOException {
		cur_accum &= masks[cur_bits];

		if (cur_bits > 0)
			cur_accum |= (code << cur_bits);
		else
			cur_accum = code;

		cur_bits += n_bits;

		while (cur_bits >= 8) {
			char_out((byte) (cur_accum & 0xff), outs);
			cur_accum >>= 8;
			cur_bits -= 8;
		}

		// If the next entry is going to be too big for the code size,
		// then increase it, if possible.
		if (free_ent > maxcode || clear_flg) {
			if (clear_flg) {
				maxcode = MAXCODE(n_bits = g_init_bits);
				clear_flg = false;
			} else {
				++n_bits;
				if (n_bits == maxbits)
					maxcode = maxmaxcode;
				else
					maxcode = MAXCODE(n_bits);
			}
		}

		if (code == EOFCode) {
			// At EOF, write the rest of the buffer.
			while (cur_bits > 0) {
				char_out((byte) (cur_accum & 0xff), outs);
				cur_accum >>= 8;
				cur_bits -= 8;
			}

			flush_char(outs);
		}
	}

	// Clear out the hash table

	// table clear for block compress
	void cl_block(OutputStream outs) throws IOException {
		cl_hash(hsize);
		free_ent = ClearCode + 2;
		clear_flg = true;

		output(ClearCode, outs);
	}

	// reset code table
	void cl_hash(int hsize) {
		for (int i = 0; i < hsize; ++i)
			htab[i] = -1;
	}

	// GIF Specific routines

	// Number of characters so far in this 'packet'
	int a_count;

	// Set up the 'byte output' routine
	void char_init() {
		a_count = 0;
	}

	// Define the storage for the packet accumulator
	byte[] accum = new byte[256];

	// Add a character to the end of the current packet, and if it is 254
	// characters, flush the packet to disk.
	void char_out(byte c, OutputStream outs) throws IOException {
		accum[a_count++] = c;
		if (a_count >= 254)
			flush_char(outs);
	}

	// Flush the packet to disk, and reset the accumulator
	void flush_char(OutputStream outs) throws IOException {
		if (a_count > 0) {
			outs.write(a_count);
			outs.write(accum, 0, a_count);
			a_count = 0;
		}
	}

}

class GifEncoderHashitem {

	public int rgb;
	public int count;
	public int index;
	public boolean isTransparent;

	public GifEncoderHashitem(int rgb, int count, int index, boolean isTransparent) {
		this.rgb = rgb;
		this.count = count;
		this.index = index;
		this.isTransparent = isTransparent;
	}

}