gifencoder.java

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        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 ([e-mail])

    // 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;
    }

}