gifimagereader.java

java1.6众多例子参考

        }
        
        // Fill in the entire table for robustness against
        // out-of-sequence codes.
  	for (int i = numEntries; i < 4096; i++) {
            prefix[i] = -1;
            length[i] = 1;
        }
        
	// tableIndex = numEntries + 2;
        // codeSize = initCodeSize + 1;
        // codeMask = (1 << codeSize) - 1;
    }

    Rectangle sourceRegion;
    int sourceXSubsampling;
    int sourceYSubsampling;
    int sourceMinProgressivePass;
    int sourceMaxProgressivePass;

    Point destinationOffset;
    Rectangle destinationRegion;

    // Used only if IIOReadUpdateListeners are present
    int updateMinY;
    int updateYStep;

    boolean decodeThisRow = true;
    int destY = 0;

    byte[] rowBuf;

    private void outputRow() {
        // Clip against ImageReadParam
        int width = Math.min(sourceRegion.width,
                             destinationRegion.width*sourceXSubsampling);
        int destX = destinationRegion.x;

        if (sourceXSubsampling == 1) {
            theTile.setDataElements(destX, destY, width, 1, rowBuf);
        } else {
            for (int x = 0; x < width; x += sourceXSubsampling, destX++) {
                theTile.setSample(destX, destY, 0, rowBuf[x] & 0xff);
            }
        }

        // Update IIOReadUpdateListeners, if any
        if (updateListeners != null) {
            int[] bands = { 0 };
            // updateYStep will have been initialized if
            // updateListeners is non-null
            processImageUpdate(theImage,
                               destX, destY,
                               width, 1, 1, updateYStep,
                               bands);
        }
    }

    private void computeDecodeThisRow() {
        this.decodeThisRow =
            (destY < destinationRegion.y + destinationRegion.height) &&
            (streamY >= sourceRegion.y) &&
            (streamY < sourceRegion.y + sourceRegion.height) &&
            (((streamY - sourceRegion.y) % sourceYSubsampling) == 0);
    }

    private void outputPixels(byte[] string, int len) {
        if (interlacePass < sourceMinProgressivePass ||
            interlacePass > sourceMaxProgressivePass) {
            return;
        }

        for (int i = 0; i < len; i++) {
            if (streamX >= sourceRegion.x) {
                rowBuf[streamX - sourceRegion.x] = string[i];
            }

            // Process end-of-row
            ++streamX;
            if (streamX == width) {
                // Update IIOReadProgressListeners
                ++rowsDone;
                processImageProgress(100.0F*rowsDone/height);

                if (decodeThisRow) {
                    outputRow();
                }
                
                streamX = 0;
                if (imageMetadata.interlaceFlag) {
                    streamY += interlaceIncrement[interlacePass];
                    if (streamY >= height) {
                        // Inform IIOReadUpdateListeners of end of pass
                        if (updateListeners != null) {
                            processPassComplete(theImage);
                        }

                        ++interlacePass;
                        if (interlacePass > sourceMaxProgressivePass) {
                            return;
                        }
                        streamY = interlaceOffset[interlacePass];
                        startPass(interlacePass);
                    }
                } else {
                    ++streamY;
                }
                
                // Determine whether pixels from this row will 
                // be written to the destination
                this.destY = destinationRegion.y +
                    (streamY - sourceRegion.y)/sourceYSubsampling;
                computeDecodeThisRow();
            }
        }
    }

    // END LZW STUFF
    
    private void readHeader() throws IIOException {
        if (gotHeader) {
            return;
        }
        if (stream == null) {
            throw new IllegalStateException("Input not set!");
        }

        // Create an object to store the stream metadata
        this.streamMetadata = new GIFStreamMetadata();

        try {
            stream.setByteOrder(ByteOrder.LITTLE_ENDIAN);
            
            byte[] signature = new byte[6];
            stream.readFully(signature);

            StringBuffer version = new StringBuffer(3);
            version.append((char)signature[3]);
            version.append((char)signature[4]);
            version.append((char)signature[5]);
            streamMetadata.version = version.toString();

            streamMetadata.logicalScreenWidth = stream.readUnsignedShort();
            streamMetadata.logicalScreenHeight = stream.readUnsignedShort();

            int packedFields = stream.readUnsignedByte();
            boolean globalColorTableFlag = (packedFields & 0x80) != 0;
            streamMetadata.colorResolution = ((packedFields >> 4) & 0x7) + 1;
            streamMetadata.sortFlag = (packedFields & 0x8) != 0;
            int numGCTEntries = 1 << ((packedFields & 0x7) + 1);

            streamMetadata.backgroundColorIndex = stream.readUnsignedByte();
            streamMetadata.pixelAspectRatio = stream.readUnsignedByte();

            if (globalColorTableFlag) {
                streamMetadata.globalColorTable = new byte[3*numGCTEntries];
                stream.readFully(streamMetadata.globalColorTable);
            } else {
                streamMetadata.globalColorTable = null;
            }

            // Found position of metadata for image 0
            imageStartPosition.add(new Long(stream.getStreamPosition()));
        } catch (IOException e) {
            throw new IIOException("I/O error reading header!", e);
        }

        gotHeader = true;
    }

    private boolean skipImage() throws IIOException {
        // Stream must be at the beginning of an image descriptor
        // upon exit 

        try {
            while (true) {
                int blockType = stream.readUnsignedByte();

                if (blockType == 0x2c) {
                    stream.skipBytes(8);

                    int packedFields = stream.readUnsignedByte();
                    if ((packedFields & 0x80) != 0) {
                        // Skip color table if any
                        int bits = (packedFields & 0x7) + 1;
                        stream.skipBytes(3*(1 << bits));
                    }

                    stream.skipBytes(1);
                    
                    int length = 0;
                    do {
                        length = stream.readUnsignedByte();
                        stream.skipBytes(length);
                    } while (length > 0);

                    return true;
                } else if (blockType == 0x3b) {
                    return false;
                } else if (blockType == 0x21) {
                    int label = stream.readUnsignedByte();

                    int length = 0;
                    do {
                        length = stream.readUnsignedByte();
                        stream.skipBytes(length);
                    } while (length > 0);
                } else if (blockType == 0x0) {
                    // EOF
                    return false;
                } else {
                    int length = 0;
                    do {
                        length = stream.readUnsignedByte();
                        stream.skipBytes(length);
                    } while (length > 0);
                }
            }
        } catch (EOFException e) {
            return false;
        } catch (IOException e) {
            throw new IIOException("I/O error locating image!", e);
        }
    }

    private int locateImage(int imageIndex) throws IIOException {
        readHeader();

        try {
            // Find closest known index
            int index = Math.min(imageIndex, imageStartPosition.size() - 1);
            
            // Seek to that position
            Long l = (Long)imageStartPosition.get(index);
            stream.seek(l.longValue());

            // Skip images until at desired index or last image found
            while (index < imageIndex) {
                if (!skipImage()) {
                    --index;
                    return index;
                }
                
                Long l1 = new Long(stream.getStreamPosition());                
                imageStartPosition.add(l1);
                ++index;
            }
        } catch (IOException e) {
            throw new IIOException("Couldn't seek!", e);
        }

        if (currIndex != imageIndex) {
            imageMetadata = null;
        }
        currIndex = imageIndex;
        return imageIndex;
    }

    // Read blocks of 1-255 bytes, stop at a 0-length block
    private byte[] concatenateBlocks() throws IOException {
        byte[] data = new byte[0];
        while (true) {
            int length = stream.readUnsignedByte();
            if (length == 0) {
                break;
            }
            byte[] newData = new byte[data.length + length];
            System.arraycopy(data, 0, newData, 0, data.length);
            stream.readFully(newData, data.length, length);
            data = newData;
        }

        return data;
    }

    // Stream must be positioned at start of metadata for 'currIndex'
    private void readMetadata() throws IIOException {
        if (stream == null) {
            throw new IllegalStateException("Input not set!");
        }

        try {
            // Create an object to store the image metadata
            this.imageMetadata = new GIFImageMetadata();
            
            long startPosition = stream.getStreamPosition();
            while (true) {
                int blockType = stream.readUnsignedByte();
                if (blockType == 0x2c) { // Image Descriptor
                    imageMetadata.imageLeftPosition =
                        stream.readUnsignedShort();
                    imageMetadata.imageTopPosition =
                        stream.readUnsignedShort();
                    imageMetadata.imageWidth = stream.readUnsignedShort();
                    imageMetadata.imageHeight = stream.readUnsignedShort();

                    int idPackedFields = stream.readUnsignedByte();
                    boolean localColorTableFlag =
                        (idPackedFields & 0x80) != 0;
                    imageMetadata.interlaceFlag = (idPackedFields & 0x40) != 0;
                    imageMetadata.sortFlag = (idPackedFields & 0x20) != 0;
                    int numLCTEntries = 1 << ((idPackedFields & 0x7) + 1);

                    if (localColorTableFlag) {
                        // Read color table if any
                        imageMetadata.localColorTable =
                            new byte[3*numLCTEntries];
                        stream.readFully(imageMetadata.localColorTable);
                    } else {
                        imageMetadata.localColorTable = null;
                    }

                    // Record length of this metadata block
                    this.imageMetadataLength =
                        (int)(stream.getStreamPosition() - startPosition);

                    // Now positioned at start of LZW-compressed pixels
                    return;
                } else if (blockType == 0x21) { // Extension block
                    int label = stream.readUnsignedByte();

                    if (label == 0xf9) { // Graphics Control Extension
                        int gceLength = stream.readUnsignedByte(); // 4
                        int gcePackedFields = stream.readUnsignedByte();
                        imageMetadata.disposalMethod =
                            (gcePackedFields >> 2) & 0x3;
                        imageMetadata.userInputFlag = 
                            (gcePackedFields & 0x2) != 0;
                        imageMetadata.transparentColorFlag =