gifimage.java

iText是一个能够快速产生PDF文件的java类库。iText的java类对于那些要产生包含文本

            switch (code) {
                
                case 0x2C:    // image separator
                    readImage();
                    break;
                    
                case 0x21:    // extension
                    code = in.read();
                    switch (code) {
                        
                        case 0xf9:    // graphics control extension
                            readGraphicControlExt();
                            break;
                            
                        case 0xff:    // application extension
                            readBlock();
                            skip();        // don't care
                            break;
                            
                        default:    // uninteresting extension
                            skip();
                    }
                    break;
                    
                default:
                    done = true;
                    break;
            }
        }
    }

    /**
     * Reads next frame image
     */
    protected void readImage() throws IOException {
        ix = readShort();    // (sub)image position & size
        iy = readShort();
        iw = readShort();
        ih = readShort();
        
        int packed = in.read();
        lctFlag = (packed & 0x80) != 0;     // 1 - local color table flag
        interlace = (packed & 0x40) != 0;   // 2 - interlace flag
        // 3 - sort flag
        // 4-5 - reserved
        lctSize = 2 << (packed & 7);        // 6-8 - local color table size
        m_bpc = newBpc(m_gbpc);
        if (lctFlag) {
            m_curr_table = readColorTable((packed & 7) + 1);   // read table
            m_bpc = newBpc((packed & 7) + 1);
        }
        else {
            m_curr_table = m_global_table;
        }
        if (transparency && transIndex >= m_curr_table.length / 3)
            transparency = false;
        if (transparency && m_bpc == 1) { // Acrobat 5.05 doesn't like this combination
            byte tp[] = new byte[12];
            System.arraycopy(m_curr_table, 0, tp, 0, 6);
            m_curr_table = tp;
            m_bpc = 2;
        }
        boolean skipZero = decodeImageData();   // decode pixel data
        if (!skipZero)
            skip();
        
        Image img = null;
        try {
            img = new ImgRaw(iw, ih, 1, m_bpc, m_out);
            PdfArray colorspace = new PdfArray();
            colorspace.add(PdfName.INDEXED);
            colorspace.add(PdfName.DEVICERGB);
            int len = m_curr_table.length;
            colorspace.add(new PdfNumber(len / 3 - 1));
            colorspace.add(new PdfString(m_curr_table));
            PdfDictionary ad = new PdfDictionary();
            ad.put(PdfName.COLORSPACE, colorspace);
            img.setAdditional(ad);
            if (transparency) {
                img.setTransparency(new int[]{transIndex, transIndex});
            }
        }
        catch (Exception e) {
            throw new ExceptionConverter(e);
        }
        img.setOriginalType(Image.ORIGINAL_GIF);
        img.setOriginalData(fromData);
        img.setUrl(fromUrl);
        GifFrame gf = new GifFrame();
        gf.image = img;
        gf.ix = ix;
        gf.iy = iy;
        frames.add(gf);   // add image to frame list
        
        //resetFrame();
        
    }
    
    protected boolean decodeImageData() throws IOException {
        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;
        boolean skipZero = false;
        
        if (prefix == null)
            prefix = new short[MaxStackSize];
        if (suffix == null)
            suffix = new byte[MaxStackSize];
        if (pixelStack == null)
            pixelStack = new byte[MaxStackSize+1];
        
        m_line_stride = (iw * m_bpc + 7) / 8;
        m_out = new byte[m_line_stride * ih];
        int pass = 1;
        int inc = interlace ? 8 : 1;
        int line = 0;
        int xpos = 0;
        
        //  Initialize GIF data stream decoder.
        
        data_size = in.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 = 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) {
                            skipZero = true;
                            break;
                        }
                        bi = 0;
                    }
                    datum += (((int) block[bi]) & 0xff) << bits;
                    bits += 8;
                    bi++;
                    count--;
                    continue;
                }
                
                //  Get the next code.
                
                code = datum & code_mask;
                datum >>= code_size;
                bits -= code_size;
                
                //  Interpret the code
                
                if ((code > available) || (code == end_of_information))
                    break;
                if (code == clear) {
                    //  Reset decoder.
                    code_size = data_size + 1;
                    code_mask = (1 << code_size) - 1;
                    available = clear + 2;
                    old_code = NullCode;
                    continue;
                }
                if (old_code == NullCode) {
                    pixelStack[top++] = suffix[code];
                    old_code = code;
                    first = code;
                    continue;
                }
                in_code = code;
                if (code == available) {
                    pixelStack[top++] = (byte) first;
                    code = old_code;
                }
                while (code > clear) {
                    pixelStack[top++] = suffix[code];
                    code = prefix[code];
                }
                first = ((int) suffix[code]) & 0xff;
                
                //  Add a new string to the string table,
                
                if (available >= MaxStackSize)
                    break;
                pixelStack[top++] = (byte) first;
                prefix[available] = (short) old_code;
                suffix[available] = (byte) first;
                available++;
                if (((available & code_mask) == 0) && (available < MaxStackSize)) {
                    code_size++;
                    code_mask += available;
                }
                old_code = in_code;
            }
            
            //  Pop a pixel off the pixel stack.
            
            top--;
            i++;
            
            setPixel(xpos, line, pixelStack[top]);
            ++xpos;
            if (xpos >= iw) {
                xpos = 0;
                line += inc;
                if (line >= ih) {
                    if (interlace) {
                        do {
                            pass++;
                            switch (pass) {
                                case 2:
                                    line = 4;
                                    break;
                                case 3:
                                    line = 2;
                                    inc = 4;
                                    break;
                                case 4:
                                    line = 1;
                                    inc = 2;
                                    break;
                                default: // this shouldn't happen
                                    line = ih - 1;
                                    inc = 0;
                            }
                        } while (line >= ih);
                    }
                    else {
                        line = ih - 1; // this shouldn't happen
                        inc = 0;
                    }
                }
            }
        }
        return skipZero;
    }
    
    
    protected void setPixel(int x, int y, int v) {
        if (m_bpc == 8) {
            int pos = x + iw * y;
            m_out[pos] = (byte)v;
        }
        else {
            int pos = m_line_stride * y + x / (8 / m_bpc);
            int vout = v << (8 - m_bpc * (x % (8 / m_bpc))- m_bpc);
            m_out[pos] |= vout;
        }
    }
    
    /**
     * Resets frame state for reading next image.
     */
    protected void resetFrame() {
        // it does nothing in the pdf context
        //boolean transparency = false;
        //int delay = 0;
    }

    /**
     * Reads Graphics Control Extension values
     */
    protected void readGraphicControlExt() throws IOException {
        in.read();    // block size
        int packed = in.read();   // packed fields
        dispose = (packed & 0x1c) >> 2;   // disposal method
        if (dispose == 0)
            dispose = 1;   // elect to keep old image if discretionary
        transparency = (packed & 1) != 0;
        delay = readShort() * 10;   // delay in milliseconds
        transIndex = in.read();        // transparent color index
        in.read();                     // block terminator
    }
    
    /**
     * Skips variable length blocks up to and including
     * next zero length block.
     */
    protected void skip() throws IOException {
        do {
            readBlock();
        } while (blockSize > 0);
    }

    static class GifFrame {
        Image image;
        int ix;
        int iy;
    }
}