gifimagereader.java

java1.6众多例子参考

/*
 * @(#)GIFImageReader.java	1.46 05/12/01
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.imageio.plugins.gif;

import java.awt.Point;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.image.WritableRaster;
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.InputStream;
import java.io.IOException;
import java.nio.ByteOrder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import javax.imageio.IIOException;
import javax.imageio.ImageReader;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.spi.ImageReaderSpi;
import javax.imageio.stream.ImageInputStream;
import com.sun.imageio.plugins.common.ReaderUtil;

/**
 * @version 0.5
 */
public class GIFImageReader extends ImageReader {

    // The current ImageInputStream source.
    ImageInputStream stream = null;

    // Per-stream settings

    // True if the file header including stream metadata has been read.
    boolean gotHeader = false;
    
    // Global metadata, read once per input setting.
    GIFStreamMetadata streamMetadata = null;

    // The current image index
    int currIndex = -1;

    // Metadata for image at 'currIndex', or null.
    GIFImageMetadata imageMetadata = null;

    // A List of Longs indicating the stream positions of the
    // start of the metadata for each image.  Entries are added
    // as needed.
    List imageStartPosition = new ArrayList();

    // Length of metadata for image at 'currIndex', valid only if
    // imageMetadata != null.
    int imageMetadataLength;

    // The number of images in the stream, if known, otherwise -1.
    int numImages = -1;

    // Variables used by the LZW decoding process
    byte[] block = new byte[255];
    int blockLength = 0;
    int bitPos = 0;
    int nextByte = 0;
    int initCodeSize;
    int clearCode;
    int eofCode;

    // 32-bit lookahead buffer
    int next32Bits = 0;

    // Try if the end of the data blocks has been found,
    // and we are simply draining the 32-bit buffer
    boolean lastBlockFound = false;

    // The image to be written.
    BufferedImage theImage = null;

    // The image's tile.
    WritableRaster theTile = null;
    
    // The image dimensions (from the stream).
    int width = -1, height = -1;

    // The pixel currently being decoded (in the stream's coordinates).
    int streamX = -1, streamY = -1;

    // The number of rows decoded
    int rowsDone = 0;

    // The current interlace pass, starting with 0.
    int interlacePass = 0;

    // End per-stream settings

    // Constants used to control interlacing.
    static final int[] interlaceIncrement = { 8, 8, 4, 2, -1 };
    static final int[] interlaceOffset = { 0, 4, 2, 1, -1 };

    public GIFImageReader(ImageReaderSpi originatingProvider) {
        super(originatingProvider);
    }

    // Take input from an ImageInputStream
    public void setInput(Object input,
                         boolean seekForwardOnly,
                         boolean ignoreMetadata) {
        super.setInput(input, seekForwardOnly, ignoreMetadata);
        if (input != null) {
            if (!(input instanceof ImageInputStream)) {
                throw new IllegalArgumentException
                    ("input not an ImageInputStream!"); 
            }
            this.stream = (ImageInputStream)input;
        } else {
            this.stream = null;
        }
        
        // Clear all values based on the previous stream contents
        resetStreamSettings();
    }

    public int getNumImages(boolean allowSearch) throws IIOException {
        if (stream == null) {
            throw new IllegalStateException("Input not set!");
        }
        if (seekForwardOnly && allowSearch) {
            throw new IllegalStateException
                ("seekForwardOnly and allowSearch can't both be true!");
        }

        if (numImages > 0) {
            return numImages;
        }
        if (allowSearch) {
            this.numImages = locateImage(Integer.MAX_VALUE) + 1;
        }
        return numImages;
    }

    // Throw an IndexOutOfBoundsException if index < minIndex,
    // and bump minIndex if required.
    private void checkIndex(int imageIndex) {
        if (imageIndex < minIndex) {
            throw new IndexOutOfBoundsException("imageIndex < minIndex!");
        }
        if (seekForwardOnly) {
            minIndex = imageIndex;
        }
    }

    public int getWidth(int imageIndex) throws IIOException {
        checkIndex(imageIndex);

        int index = locateImage(imageIndex);
        if (index != imageIndex) {
            throw new IndexOutOfBoundsException();
        }
        readMetadata();
        return imageMetadata.imageWidth;
    }

    public int getHeight(int imageIndex) throws IIOException {
        checkIndex(imageIndex);

        int index = locateImage(imageIndex);
        if (index != imageIndex) {
            throw new IndexOutOfBoundsException();
        }
        readMetadata();
        return imageMetadata.imageHeight;
    }

    public Iterator getImageTypes(int imageIndex) throws IIOException {
        checkIndex(imageIndex);

        int index = locateImage(imageIndex);
        if (index != imageIndex) {
            throw new IndexOutOfBoundsException();
        }
        readMetadata();

        List l = new ArrayList(1);

        byte[] colorTable;
        if (imageMetadata.localColorTable != null) {
            colorTable = imageMetadata.localColorTable;
        } else {
            colorTable = streamMetadata.globalColorTable;
        }

        // Normalize color table length to 2^1, 2^2, 2^4, or 2^8
        int length = colorTable.length/3;
        int bits;
        if (length == 2) {
            bits = 1;
        } else if (length == 4) {
            bits = 2;
        } else if (length == 8 || length == 16) {
            // Bump from 3 to 4 bits
            bits = 4;
        } else {
            // Bump to 8 bits
            bits = 8;
        }
        int lutLength = 1 << bits;
        byte[] r = new byte[lutLength];
        byte[] g = new byte[lutLength];
        byte[] b = new byte[lutLength];

        // Entries from length + 1 to lutLength - 1 will be 0
        int rgbIndex = 0;
        for (int i = 0; i < length; i++) {
            r[i] = colorTable[rgbIndex++];
            g[i] = colorTable[rgbIndex++];
            b[i] = colorTable[rgbIndex++];
        }

        byte[] a = null;
        if (imageMetadata.transparentColorFlag) {
            a = new byte[lutLength];
            Arrays.fill(a, (byte)255);
            
            // Some files erroneously have a transparent color index
            // of 255 even though there are fewer than 256 colors.
            int idx = Math.min(imageMetadata.transparentColorIndex,
                               lutLength - 1);
            a[idx] = (byte)0;
        }

        int[] bitsPerSample = new int[1];
        bitsPerSample[0] = bits;
        l.add(ImageTypeSpecifier.createIndexed(r, g, b, a, bits,
                                               DataBuffer.TYPE_BYTE));
        return l.iterator();
    }

    public ImageReadParam getDefaultReadParam() {
        return new ImageReadParam();
    }

    public IIOMetadata getStreamMetadata() throws IIOException {
        readHeader();
        return streamMetadata;
    }

    public IIOMetadata getImageMetadata(int imageIndex) throws IIOException {
        checkIndex(imageIndex);

        int index = locateImage(imageIndex);
        if (index != imageIndex) {
            throw new IndexOutOfBoundsException("Bad image index!");
        }
        readMetadata();
        return imageMetadata;
    }

    // BEGIN LZW STUFF

    private void initNext32Bits() {
        next32Bits = block[0] & 0xff;
        next32Bits |= (block[1] & 0xff) << 8;
        next32Bits |= (block[2] & 0xff) << 16;
        next32Bits |= block[3] << 24;
        nextByte = 4;
    }

    // Load a block (1-255 bytes) at a time, and maintain
    // a 32-bit lookahead buffer that is filled from the left
    // and extracted from the right.
    //
    // When the last block is found, we continue to 
    //
    private int getCode(int codeSize, int codeMask) throws IOException {
        if (bitPos + codeSize > 32) {
            return eofCode; // No more data available
        }

        int code = (next32Bits >> bitPos) & codeMask;
        bitPos += codeSize;

        // Shift in a byte of new data at a time
        while (bitPos >= 8 && !lastBlockFound) {
            next32Bits >>>= 8;
            bitPos -= 8;
            
            // Check if current block is out of bytes
            if (nextByte >= blockLength) {
                // Get next block size
                blockLength = stream.readUnsignedByte();
                if (blockLength == 0) {
                    lastBlockFound = true;
                    return code;
                } else {
                    int left = blockLength;
                    int off = 0;
                    while (left > 0) {
                        int nbytes = stream.read(block, off, left);
                        off += nbytes;
                        left -= nbytes;
                    }
                    nextByte = 0;
                }
            }

            next32Bits |= block[nextByte++] << 24;
        }

        return code;
    }

    public void initializeStringTable(int[] prefix,
                                      byte[] suffix,
                                      byte[] initial,
                                      int[] length) {
        int numEntries = 1 << initCodeSize;
  	for (int i = 0; i < numEntries; i++) {
            prefix[i] = -1;
            suffix[i] = (byte)i;
            initial[i] = (byte)i;
            length[i] = 1;