JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.imageio.plugins.gif;

import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.image.ColorModel;
import java.awt.image.ComponentSampleModel;
import java.awt.image.DataBufferByte;
import java.awt.image.IndexColorModel;
import java.awt.image.Raster;
import java.awt.image.RenderedImage;
import java.awt.image.SampleModel;
import java.awt.image.WritableRaster;
import java.io.IOException;
import java.nio.ByteOrder;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Locale;
import javax.imageio.IIOException;
import javax.imageio.IIOImage;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.spi.ImageWriterSpi;
import javax.imageio.metadata.IIOInvalidTreeException;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.metadata.IIOMetadataFormatImpl;
import javax.imageio.metadata.IIOMetadataNode;
import javax.imageio.stream.ImageOutputStream;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import com.sun.imageio.plugins.common.LZWCompressor;
import com.sun.imageio.plugins.common.PaletteBuilder;
import sun.awt.image.ByteComponentRaster;

public class GIFImageWriter extends ImageWriter {
    private static final boolean DEBUG = false; // XXX false for release!

    static final String STANDARD_METADATA_NAME =
    IIOMetadataFormatImpl.standardMetadataFormatName;

    static final String STREAM_METADATA_NAME =
    GIFWritableStreamMetadata.NATIVE_FORMAT_NAME;

    static final String IMAGE_METADATA_NAME =
    GIFWritableImageMetadata.NATIVE_FORMAT_NAME;

    /**
     * The {@code output} case to an {@code ImageOutputStream}.
     */
    private ImageOutputStream stream = null;

    /**
     * Whether a sequence is being written.
     */
    private boolean isWritingSequence = false;

    /**
     * Whether the header has been written.
     */
    private boolean wroteSequenceHeader = false;

    /**
     * The stream metadata of a sequence.
     */
    private GIFWritableStreamMetadata theStreamMetadata = null;

    /**
     * The index of the image being written.
     */
    private int imageIndex = 0;

    /**
     * The number of bits represented by the value which should be a
     * legal length for a color table.
     */
    private static int getNumBits(int value) throws IOException {
        int numBits;
        switch(value) {
        case 2:
            numBits = 1;
            break;
        case 4:
            numBits = 2;
            break;
        case 8:
            numBits = 3;
            break;
        case 16:
            numBits = 4;
            break;
        case 32:
            numBits = 5;
            break;
        case 64:
            numBits = 6;
            break;
        case 128:
            numBits = 7;
            break;
        case 256:
            numBits = 8;
            break;
        default:
            throw new IOException("Bad palette length: "+value+"!");
        }

        return numBits;
    }

    /**
     * Compute the source region and destination dimensions taking any
     * parameter settings into account.
     */
    private static void computeRegions(Rectangle sourceBounds,
                                       Dimension destSize,
                                       ImageWriteParam p) {
        ImageWriteParam param;
        int periodX = 1;
        int periodY = 1;
        if (p != null) {
            int[] sourceBands = p.getSourceBands();
            if (sourceBands != null &&
                (sourceBands.length != 1 ||
                 sourceBands[0] != 0)) {
                throw new IllegalArgumentException("Cannot sub-band image!");
            }

            // Get source region and subsampling factors
            Rectangle sourceRegion = p.getSourceRegion();
            if (sourceRegion != null) {
                // Clip to actual image bounds
                sourceRegion = sourceRegion.intersection(sourceBounds);
                sourceBounds.setBounds(sourceRegion);
            }

            // Adjust for subsampling offsets
            int gridX = p.getSubsamplingXOffset();
            int gridY = p.getSubsamplingYOffset();
            sourceBounds.x += gridX;
            sourceBounds.y += gridY;
            sourceBounds.width -= gridX;
            sourceBounds.height -= gridY;

            // Get subsampling factors
            periodX = p.getSourceXSubsampling();
            periodY = p.getSourceYSubsampling();
        }

        // Compute output dimensions
        destSize.setSize((sourceBounds.width + periodX - 1)/periodX,
                         (sourceBounds.height + periodY - 1)/periodY);
        if (destSize.width <= 0 || destSize.height <= 0) {
            throw new IllegalArgumentException("Empty source region!");
        }
    }

    /**
     * Create a color table from the image ColorModel and SampleModel.
     */
    private static byte[] createColorTable(ColorModel colorModel,
                                           SampleModel sampleModel)
    {
        byte[] colorTable;
        if (colorModel instanceof IndexColorModel) {
            IndexColorModel icm = (IndexColorModel)colorModel;
            int mapSize = icm.getMapSize();

            /**
             * The GIF image format assumes that size of image palette
             * is power of two. We will use closest larger power of two
             * as size of color table.
             */
            int ctSize = getGifPaletteSize(mapSize);

            byte[] reds = new byte[ctSize];
            byte[] greens = new byte[ctSize];
            byte[] blues = new byte[ctSize];
            icm.getReds(reds);
            icm.getGreens(greens);
            icm.getBlues(blues);

            /**
             * fill tail of color component arrays by replica of first color
             * in order to avoid appearance of extra colors in the color table
             */
            for (int i = mapSize; i < ctSize; i++) {
                reds[i] = reds[0];
                greens[i] = greens[0];
                blues[i] = blues[0];
            }

            colorTable = new byte[3*ctSize];
            int idx = 0;
            for (int i = 0; i < ctSize; i++) {
                colorTable[idx++] = reds[i];
                colorTable[idx++] = greens[i];
                colorTable[idx++] = blues[i];
            }
        } else if (sampleModel.getNumBands() == 1) {
            // create gray-scaled color table for single-banded images
            int numBits = sampleModel.getSampleSize()[0];
            if (numBits > 8) {
                numBits = 8;
            }
            int colorTableLength = 3*(1 << numBits);
            colorTable = new byte[colorTableLength];
            for (int i = 0; i < colorTableLength; i++) {
                colorTable[i] = (byte)(i/3);
            }
        } else {
            // We do not have enough information here
            // to create well-fit color table for RGB image.
            colorTable = null;
        }

        return colorTable;
    }

    /**
     * According do GIF specification size of clor table (palette here)
     * must be in range from 2 to 256 and must be power of 2.
     */
    private static int getGifPaletteSize(int x) {
        if (x <= 2) {
            return 2;
        }
        x = x - 1;
        x = x | (x >> 1);
        x = x | (x >> 2);
        x = x | (x >> 4);
        x = x | (x >> 8);
        x = x | (x >> 16);
        return x + 1;
    }



    public GIFImageWriter(GIFImageWriterSpi originatingProvider) {
        super(originatingProvider);
        if (DEBUG) {
            System.err.println("GIF Writer is created");
        }
    }

    public boolean canWriteSequence() {
        return true;
    }

    /**
     * Merges {@code inData} into {@code outData}. The supplied
     * metadata format name is attempted first and failing that the standard
     * metadata format name is attempted.
     */
    private void convertMetadata(String metadataFormatName,
                                 IIOMetadata inData,
                                 IIOMetadata outData) {
        String formatName = null;

        String nativeFormatName = inData.getNativeMetadataFormatName();
        if (nativeFormatName != null &&
            nativeFormatName.equals(metadataFormatName)) {
            formatName = metadataFormatName;
        } else {
            String[] extraFormatNames = inData.getExtraMetadataFormatNames();

            if (extraFormatNames != null) {
                for (int i = 0; i < extraFormatNames.length; i++) {
                    if (extraFormatNames[i].equals(metadataFormatName)) {
                        formatName = metadataFormatName;
                        break;
                    }
                }
            }
        }

        if (formatName == null &&
            inData.isStandardMetadataFormatSupported()) {
            formatName = STANDARD_METADATA_NAME;
        }

        if (formatName != null) {
            try {
                Node root = inData.getAsTree(formatName);
                outData.mergeTree(formatName, root);
            } catch(IIOInvalidTreeException e) {
                // ignore
            }
        }
    }

    /**
     * Creates a default stream metadata object and merges in the
     * supplied metadata.
     */
    public IIOMetadata convertStreamMetadata(IIOMetadata inData,
                                             ImageWriteParam param) {
        if (inData == null) {
            throw new IllegalArgumentException("inData == null!");
        }

        IIOMetadata sm = getDefaultStreamMetadata(param);

        convertMetadata(STREAM_METADATA_NAME, inData, sm);

        return sm;
    }

    /**
     * Creates a default image metadata object and merges in the
     * supplied metadata.
     */
    public IIOMetadata convertImageMetadata(IIOMetadata inData,
                                            ImageTypeSpecifier imageType,
                                            ImageWriteParam param) {
        if (inData == null) {
            throw new IllegalArgumentException("inData == null!");
        }
        if (imageType == null) {
            throw new IllegalArgumentException("imageType == null!");
        }

        GIFWritableImageMetadata im =
            (GIFWritableImageMetadata)getDefaultImageMetadata(imageType,
                                                              param);

        // Save interlace flag state.

        boolean isProgressive = im.interlaceFlag;

        convertMetadata(IMAGE_METADATA_NAME, inData, im);

        // Undo change to interlace flag if not MODE_COPY_FROM_METADATA.

        if (param != null && param.canWriteProgressive() &&
            param.getProgressiveMode() != ImageWriteParam.MODE_COPY_FROM_METADATA) {
            im.interlaceFlag = isProgressive;
        }

        return im;
    }

    public void endWriteSequence() throws IOException {
        if (stream == null) {
            throw new IllegalStateException("output == null!");
        }
        if (!isWritingSequence) {
            throw new IllegalStateException("prepareWriteSequence() was not invoked!");
        }
        writeTrailer();
        resetLocal();
    }

    public IIOMetadata getDefaultImageMetadata(ImageTypeSpecifier imageType,
                                               ImageWriteParam param) {
        GIFWritableImageMetadata imageMetadata =
            new GIFWritableImageMetadata();

        // Image dimensions

        SampleModel sampleModel = imageType.getSampleModel();

        Rectangle sourceBounds = new Rectangle(sampleModel.getWidth(),
                                               sampleModel.getHeight());
        Dimension destSize = new Dimension();
        computeRegions(sourceBounds, destSize, param);

        imageMetadata.imageWidth = destSize.width;
        imageMetadata.imageHeight = destSize.height;

        // Interlacing

        if (param != null && param.canWriteProgressive() &&
            param.getProgressiveMode() == ImageWriteParam.MODE_DISABLED) {
            imageMetadata.interlaceFlag = false;
        } else {
            imageMetadata.interlaceFlag = true;
        }

        // Local color table

        ColorModel colorModel = imageType.getColorModel();

        imageMetadata.localColorTable =
            createColorTable(colorModel, sampleModel);

        // Transparency

        if (colorModel instanceof IndexColorModel) {
            int transparentIndex =
                ((IndexColorModel)colorModel).getTransparentPixel();
            if (transparentIndex != -1) {
                imageMetadata.transparentColorFlag = true;
                imageMetadata.transparentColorIndex = transparentIndex;
            }
        }

        return imageMetadata;
    }

    public IIOMetadata getDefaultStreamMetadata(ImageWriteParam param) {
        GIFWritableStreamMetadata streamMetadata =
            new GIFWritableStreamMetadata();
        streamMetadata.version = "89a";
        return streamMetadata;
    }

    public ImageWriteParam getDefaultWriteParam() {
        return new GIFImageWriteParam(getLocale());
    }

    public void prepareWriteSequence(IIOMetadata streamMetadata)
      throws IOException {

        if (stream == null) {
            throw new IllegalStateException("Output is not set.");
        }

        resetLocal();

        // Save the possibly converted stream metadata as an instance variable.
        if (streamMetadata == null) {
            this.theStreamMetadata =
                (GIFWritableStreamMetadata)getDefaultStreamMetadata(null);
        } else {
            this.theStreamMetadata = new GIFWritableStreamMetadata();
            convertMetadata(STREAM_METADATA_NAME, streamMetadata,
                            theStreamMetadata);
        }

        this.isWritingSequence = true;
    }

    public void reset() {
        super.reset();
        resetLocal();
    }

    /**
     * Resets locally defined instance variables.
     */
    private void resetLocal() {
        this.isWritingSequence = false;
        this.wroteSequenceHeader = false;
        this.theStreamMetadata = null;
        this.imageIndex = 0;
    }

    public void setOutput(Object output) {
        super.setOutput(output);
        if (output != null) {
            if (!(output instanceof ImageOutputStream)) {
                throw new
                    IllegalArgumentException("output is not an ImageOutputStream");
            }
            this.stream = (ImageOutputStream)output;
            this.stream.setByteOrder(ByteOrder.LITTLE_ENDIAN);
        } else {
            this.stream = null;
        }
    }

    public void write(IIOMetadata sm,
                      IIOImage iioimage,
                      ImageWriteParam p) throws IOException {
        if (stream == null) {
            throw new IllegalStateException("output == null!");
        }
        if (iioimage == null) {
            throw new IllegalArgumentException("iioimage == null!");
        }
        if (iioimage.hasRaster()) {
            throw new UnsupportedOperationException("canWriteRasters() == false!");
        }

        resetLocal();

        GIFWritableStreamMetadata streamMetadata;
        if (sm == null) {
            streamMetadata =
                (GIFWritableStreamMetadata)getDefaultStreamMetadata(p);
        } else {
            streamMetadata =
                (GIFWritableStreamMetadata)convertStreamMetadata(sm, p);
        }

        write(true, true, streamMetadata, iioimage, p);
    }

    public void writeToSequence(IIOImage image, ImageWriteParam param)
      throws IOException {
        if (stream == null) {
            throw new IllegalStateException("output == null!");
        }
        if (image == null) {
            throw new IllegalArgumentException("image == null!");
        }
        if (image.hasRaster()) {
            throw new UnsupportedOperationException("canWriteRasters() == false!");
        }
        if (!isWritingSequence) {
            throw new IllegalStateException("prepareWriteSequence() was not invoked!");
        }

        write(!wroteSequenceHeader, false, theStreamMetadata,
              image, param);

        if (!wroteSequenceHeader) {
            wroteSequenceHeader = true;
        }

        this.imageIndex++;
    }


    private boolean needToCreateIndex(RenderedImage image) {

        SampleModel sampleModel = image.getSampleModel();
        ColorModel colorModel = image.getColorModel();

        return sampleModel.getNumBands() != 1 ||
            sampleModel.getSampleSize()[0] > 8 ||
            colorModel.getComponentSize()[0] > 8;
    }

    /**
     * Writes any extension blocks, the Image Descriptor, the image data,
     * and optionally the header (Signature and Logical Screen Descriptor)
     * and trailer (Block Terminator).
     *
     * @param writeHeader Whether to write the header.
     * @param writeTrailer Whether to write the trailer.
     * @param sm The stream metadata or {@code null} if
     * {@code writeHeader} is {@code false}.
     * @param iioimage The image and image metadata.
     * @param p The write parameters.
     *
     * @throws IllegalArgumentException if the number of bands is not 1.
     * @throws IllegalArgumentException if the number of bits per sample is
     * greater than 8.
     * @throws IllegalArgumentException if the color component size is
     * greater than 8.
     * @throws IllegalArgumentException if {@code writeHeader} is
     * {@code true} and {@code sm} is {@code null}.
     * @throws IllegalArgumentException if {@code writeHeader} is
     * {@code false} and a sequence is not being written.
     */
    private void write(boolean writeHeader,
                       boolean writeTrailer,
                       IIOMetadata sm,
                       IIOImage iioimage,
                       ImageWriteParam p) throws IOException {

        RenderedImage image = iioimage.getRenderedImage();

        // Check for ability to encode image.
        if (needToCreateIndex(image)) {
            image = PaletteBuilder.createIndexedImage(image);
            iioimage.setRenderedImage(image);
        }

        ColorModel colorModel = image.getColorModel();
        SampleModel sampleModel = image.getSampleModel();

        // Determine source region and destination dimensions.
        Rectangle sourceBounds = new Rectangle(image.getMinX(),
                                               image.getMinY(),
                                               image.getWidth(),
                                               image.getHeight());
        Dimension destSize = new Dimension();
        computeRegions(sourceBounds, destSize, p);

        // Convert any provided image metadata.
        GIFWritableImageMetadata imageMetadata = null;
        if (iioimage.getMetadata() != null) {
            imageMetadata = new GIFWritableImageMetadata();
            convertMetadata(IMAGE_METADATA_NAME, iioimage.getMetadata(),
                            imageMetadata);
            // Converted rgb image can use palette different from global.
            // In order to avoid color artefacts we want to be sure we use
            // appropriate palette. For this we initialize local color table
            // from current color and sample models.
            // At this point we can guarantee that local color table can be
            // build because image was already converted to indexed or
            // gray-scale representations
            if (imageMetadata.localColorTable == null) {
                imageMetadata.localColorTable =
                    createColorTable(colorModel, sampleModel);

                // in case of indexed image we should take care of
                // transparent pixels
                if (colorModel instanceof IndexColorModel) {
                    IndexColorModel icm =
                        (IndexColorModel)colorModel;
                    int index = icm.getTransparentPixel();
                    imageMetadata.transparentColorFlag = (index != -1);
                    if (imageMetadata.transparentColorFlag) {
                        imageMetadata.transparentColorIndex = index;
                    }
                    /* NB: transparentColorFlag might have not beed reset for
                       greyscale images but explicitly reseting it here
                       is potentially not right thing to do until we have way
                       to find whether current value was explicitly set by
                       the user.
                    */
                }
            }
        }

        // Global color table values.
        byte[] globalColorTable = null;

        // Write the header (Signature+Logical Screen Descriptor+
        // Global Color Table).
        if (writeHeader) {
            if (sm == null) {
                throw new IllegalArgumentException("Cannot write null header!");
            }

            GIFWritableStreamMetadata streamMetadata =
                (GIFWritableStreamMetadata)sm;

            // Set the version if not set.
            if (streamMetadata.version == null) {
                streamMetadata.version = "89a";
            }

            // Set the Logical Screen Desriptor if not set.
            if (streamMetadata.logicalScreenWidth ==
                GIFMetadata.UNDEFINED_INTEGER_VALUE)
            {
                streamMetadata.logicalScreenWidth = destSize.width;
            }

            if (streamMetadata.logicalScreenHeight ==
                GIFMetadata.UNDEFINED_INTEGER_VALUE)
            {
                streamMetadata.logicalScreenHeight = destSize.height;
            }

            if (streamMetadata.colorResolution ==
                GIFMetadata.UNDEFINED_INTEGER_VALUE)
            {
                streamMetadata.colorResolution = colorModel != null ?
                    colorModel.getComponentSize()[0] :
                    sampleModel.getSampleSize()[0];
            }

            // Set the Global Color Table if not set, i.e., if not
            // provided in the stream metadata.
            if (streamMetadata.globalColorTable == null) {
                if (isWritingSequence && imageMetadata != null &&
                    imageMetadata.localColorTable != null) {
                    // Writing a sequence and a local color table was
                    // provided in the metadata of the first image: use it.
                    streamMetadata.globalColorTable =
                        imageMetadata.localColorTable;
                } else if (imageMetadata == null ||
                           imageMetadata.localColorTable == null) {
                    // Create a color table.
                    streamMetadata.globalColorTable =
                        createColorTable(colorModel, sampleModel);
                }
            }

            // Set the Global Color Table. At this point it should be
            // A) the global color table provided in stream metadata, if any;
            // B) the local color table of the image metadata, if any, if
            //    writing a sequence;
            // C) a table created on the basis of the first image ColorModel
            //    and SampleModel if no local color table is available; or
            // D) null if none of the foregoing conditions obtain (which
            //    should only be if a sequence is not being written and
            //    a local color table is provided in image metadata).
            globalColorTable = streamMetadata.globalColorTable;

            // Write the header.
            int bitsPerPixel;
            if (globalColorTable != null) {
                bitsPerPixel = getNumBits(globalColorTable.length/3);
            } else if (imageMetadata != null &&
                       imageMetadata.localColorTable != null) {
                bitsPerPixel =
                    getNumBits(imageMetadata.localColorTable.length/3);
            } else {
                bitsPerPixel = sampleModel.getSampleSize(0);
            }
            writeHeader(streamMetadata, bitsPerPixel);
        } else if (isWritingSequence) {
            globalColorTable = theStreamMetadata.globalColorTable;
        } else {
            throw new IllegalArgumentException("Must write header for single image!");
        }

        // Write extension blocks, Image Descriptor, and image data.
        writeImage(iioimage.getRenderedImage(), imageMetadata, p,
                   globalColorTable, sourceBounds, destSize);

        // Write the trailer.
        if (writeTrailer) {
            writeTrailer();
        }
    }

    /**
     * Writes any extension blocks, the Image Descriptor, and the image data
     *
     * @param image The image.
     * @param imageMetadata The image metadata.
     * @param param The write parameters.
     * @param globalColorTable The Global Color Table.
     * @param sourceBounds The source region.
     * @param destSize The destination dimensions.
     */
    private void writeImage(RenderedImage image,
                            GIFWritableImageMetadata imageMetadata,
                            ImageWriteParam param, byte[] globalColorTable,
                            Rectangle sourceBounds, Dimension destSize)
      throws IOException {
        ColorModel colorModel = image.getColorModel();
        SampleModel sampleModel = image.getSampleModel();

        boolean writeGraphicsControlExtension;
        if (imageMetadata == null) {
            // Create default metadata.
            imageMetadata = (GIFWritableImageMetadata)getDefaultImageMetadata(
                new ImageTypeSpecifier(image), param);

            // Set GraphicControlExtension flag only if there is
            // transparency.
            writeGraphicsControlExtension = imageMetadata.transparentColorFlag;
        } else {
            // Check for GraphicControlExtension element.
            NodeList list = null;
            try {
                IIOMetadataNode root = (IIOMetadataNode)
                    imageMetadata.getAsTree(IMAGE_METADATA_NAME);
                list = root.getElementsByTagName("GraphicControlExtension");
            } catch(IllegalArgumentException iae) {
                // Should never happen.
            }

            // Set GraphicControlExtension flag if element present.
            writeGraphicsControlExtension =
                list != null && list.getLength() > 0;

            // If progressive mode is not MODE_COPY_FROM_METADATA, ensure
            // the interlacing is set per the ImageWriteParam mode setting.
            if (param != null && param.canWriteProgressive()) {
                if (param.getProgressiveMode() ==
                    ImageWriteParam.MODE_DISABLED) {
                    imageMetadata.interlaceFlag = false;
                } else if (param.getProgressiveMode() ==
                           ImageWriteParam.MODE_DEFAULT) {
                    imageMetadata.interlaceFlag = true;
                }
            }
        }

        // Unset local color table if equal to global color table.
        if (Arrays.equals(globalColorTable, imageMetadata.localColorTable)) {
            imageMetadata.localColorTable = null;
        }

        // Override dimensions
        imageMetadata.imageWidth = destSize.width;
        imageMetadata.imageHeight = destSize.height;

        // Write Graphics Control Extension.
        if (writeGraphicsControlExtension) {
            writeGraphicControlExtension(imageMetadata);
        }

        // Write extension blocks.
        writePlainTextExtension(imageMetadata);
        writeApplicationExtension(imageMetadata);
        writeCommentExtension(imageMetadata);

        // Write Image Descriptor
        int bitsPerPixel =
            getNumBits(imageMetadata.localColorTable == null ?
                       (globalColorTable == null ?
                        sampleModel.getSampleSize(0) :
                        globalColorTable.length/3) :
                       imageMetadata.localColorTable.length/3);
        writeImageDescriptor(imageMetadata, bitsPerPixel);

        // Write image data
        writeRasterData(image, sourceBounds, destSize,
                        param, imageMetadata.interlaceFlag);
    }

    private void writeRows(RenderedImage image, LZWCompressor compressor,
                           int sx, int sdx, int sy, int sdy, int sw,
                           int dy, int ddy, int dw, int dh,
                           int numRowsWritten, int progressReportRowPeriod)
      throws IOException {
        if (DEBUG) System.out.println("Writing unoptimized");

        int[] sbuf = new int[sw];
        byte[] dbuf = new byte[dw];

        Raster raster =
            image.getNumXTiles() == 1 && image.getNumYTiles() == 1 ?
            image.getTile(0, 0) : image.getData();
        for (int y = dy; y < dh; y += ddy) {
            if (numRowsWritten % progressReportRowPeriod == 0) {
                processImageProgress((numRowsWritten*100.0F)/dh);
                if (abortRequested()) {
                    processWriteAborted();
                    return;
                }
            }

            raster.getSamples(sx, sy, sw, 1, 0, sbuf);
            for (int i = 0, j = 0; i < dw; i++, j += sdx) {
                dbuf[i] = (byte)sbuf[j];
            }
            compressor.compress(dbuf, 0, dw);
            numRowsWritten++;
            sy += sdy;
        }
    }

    private void writeRowsOpt(byte[] data, int offset, int lineStride,
                              LZWCompressor compressor,
                              int dy, int ddy, int dw, int dh,
                              int numRowsWritten, int progressReportRowPeriod)
      throws IOException {
        if (DEBUG) System.out.println("Writing optimized");

        offset += dy*lineStride;
        lineStride *= ddy;
        for (int y = dy; y < dh; y += ddy) {
            if (numRowsWritten % progressReportRowPeriod == 0) {
                processImageProgress((numRowsWritten*100.0F)/dh);
                if (abortRequested()) {
                    processWriteAborted();
                    return;
                }
            }

            compressor.compress(data, offset, dw);
            numRowsWritten++;
            offset += lineStride;
        }
    }

    private void writeRasterData(RenderedImage image,
                                 Rectangle sourceBounds,
                                 Dimension destSize,
                                 ImageWriteParam param,
                                 boolean interlaceFlag) throws IOException {

        int sourceXOffset = sourceBounds.x;
        int sourceYOffset = sourceBounds.y;
        int sourceWidth = sourceBounds.width;
        int sourceHeight = sourceBounds.height;

        int destWidth = destSize.width;
        int destHeight = destSize.height;

        int periodX;
        int periodY;
        if (param == null) {
            periodX = 1;
            periodY = 1;
        } else {
            periodX = param.getSourceXSubsampling();
            periodY = param.getSourceYSubsampling();
        }

        SampleModel sampleModel = image.getSampleModel();
        int bitsPerPixel = sampleModel.getSampleSize()[0];

        int initCodeSize = bitsPerPixel;
        if (initCodeSize == 1) {
            initCodeSize++;
        }
        stream.write(initCodeSize);

        LZWCompressor compressor =
            new LZWCompressor(stream, initCodeSize, false);

        /* At this moment we know that input image is indexed image.
         * We can directly copy data iff:
         *   - no subsampling required (periodX = 1, periodY = 0)
         *   - we can access data directly (image is non-tiled,
         *     i.e. image data are in single block)
         *   - we can calculate offset in data buffer (next 3 lines)
         */
        boolean isOptimizedCase =
            periodX == 1 && periodY == 1 &&
            image.getNumXTiles() == 1 && image.getNumYTiles() == 1 &&
            sampleModel instanceof ComponentSampleModel &&
            image.getTile(0, 0) instanceof ByteComponentRaster &&
            image.getTile(0, 0).getDataBuffer() instanceof DataBufferByte;

        int numRowsWritten = 0;

        int progressReportRowPeriod = Math.max(destHeight/20, 1);

        clearAbortRequest();
        processImageStarted(imageIndex);
        if (abortRequested()) {
            processWriteAborted();
            return;
        }

        if (interlaceFlag) {
            if (DEBUG) System.out.println("Writing interlaced");

            if (isOptimizedCase) {
                ByteComponentRaster tile =
                    (ByteComponentRaster)image.getTile(0, 0);
                byte[] data = ((DataBufferByte)tile.getDataBuffer()).getData();
                ComponentSampleModel csm =
                    (ComponentSampleModel)tile.getSampleModel();
                int offset = csm.getOffset(sourceXOffset, sourceYOffset, 0);
                // take into account the raster data offset
                offset += tile.getDataOffset(0);
                int lineStride = csm.getScanlineStride();

                writeRowsOpt(data, offset, lineStride, compressor,
                             0, 8, destWidth, destHeight,
                             numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += destHeight/8;

                writeRowsOpt(data, offset, lineStride, compressor,
                             4, 8, destWidth, destHeight,
                             numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += (destHeight - 4)/8;

                writeRowsOpt(data, offset, lineStride, compressor,
                             2, 4, destWidth, destHeight,
                             numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += (destHeight - 2)/4;

                writeRowsOpt(data, offset, lineStride, compressor,
                             1, 2, destWidth, destHeight,
                             numRowsWritten, progressReportRowPeriod);
                if (abortRequested()) {
                    return;
                }
            } else {
                writeRows(image, compressor,
                          sourceXOffset, periodX,
                          sourceYOffset, 8*periodY,
                          sourceWidth,
                          0, 8, destWidth, destHeight,
                          numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += destHeight/8;

                writeRows(image, compressor, sourceXOffset, periodX,
                          sourceYOffset + 4*periodY, 8*periodY,
                          sourceWidth,
                          4, 8, destWidth, destHeight,
                          numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += (destHeight - 4)/8;

                writeRows(image, compressor, sourceXOffset, periodX,
                          sourceYOffset + 2*periodY, 4*periodY,
                          sourceWidth,
                          2, 4, destWidth, destHeight,
                          numRowsWritten, progressReportRowPeriod);

                if (abortRequested()) {
                    return;
                }

                numRowsWritten += (destHeight - 2)/4;

                writeRows(image, compressor, sourceXOffset, periodX,
                          sourceYOffset + periodY, 2*periodY,
                          sourceWidth,
                          1, 2, destWidth, destHeight,
                          numRowsWritten, progressReportRowPeriod);
                if (abortRequested()) {
                    return;
                }
            }
        } else {
            if (DEBUG) System.out.println("Writing non-interlaced");

            if (isOptimizedCase) {
                Raster tile = image.getTile(0, 0);
                byte[] data = ((DataBufferByte)tile.getDataBuffer()).getData();
                ComponentSampleModel csm =
                    (ComponentSampleModel)tile.getSampleModel();
                int offset = csm.getOffset(sourceXOffset, sourceYOffset, 0);
                int lineStride = csm.getScanlineStride();

                writeRowsOpt(data, offset, lineStride, compressor,
                             0, 1, destWidth, destHeight,
                             numRowsWritten, progressReportRowPeriod);
                if (abortRequested()) {
                    return;
                }
            } else {
                writeRows(image, compressor,
                          sourceXOffset, periodX,
                          sourceYOffset, periodY,
                          sourceWidth,
                          0, 1, destWidth, destHeight,
                          numRowsWritten, progressReportRowPeriod);
                if (abortRequested()) {
                    return;
                }
            }
        }

        compressor.flush();

        stream.write(0x00);

        processImageComplete();
    }

    private void writeHeader(String version,
                             int logicalScreenWidth,
                             int logicalScreenHeight,
                             int colorResolution,
                             int pixelAspectRatio,
                             int backgroundColorIndex,
                             boolean sortFlag,
                             int bitsPerPixel,
                             byte[] globalColorTable) throws IOException {
        try {
            // Signature
            stream.writeBytes("GIF"+version);

            // Screen Descriptor
            // Width
            stream.writeShort((short)logicalScreenWidth);

            // Height
            stream.writeShort((short)logicalScreenHeight);

            // Global Color Table
            // Packed fields
            int packedFields = globalColorTable != null ? 0x80 : 0x00;
            packedFields |= ((colorResolution - 1) & 0x7) << 4;
            if (sortFlag) {
                packedFields |= 0x8;
            }
            packedFields |= (bitsPerPixel - 1);
            stream.write(packedFields);

            // Background color index
            stream.write(backgroundColorIndex);

            // Pixel aspect ratio
            stream.write(pixelAspectRatio);

            // Global Color Table
            if (globalColorTable != null) {
                stream.write(globalColorTable);
            }
        } catch (IOException e) {
            throw new IIOException("I/O error writing header!", e);
        }
    }

    private void writeHeader(IIOMetadata streamMetadata, int bitsPerPixel)
      throws IOException {

        GIFWritableStreamMetadata sm;
        if (streamMetadata instanceof GIFWritableStreamMetadata) {
            sm = (GIFWritableStreamMetadata)streamMetadata;
        } else {
            sm = new GIFWritableStreamMetadata();
            Node root =
                streamMetadata.getAsTree(STREAM_METADATA_NAME);
            sm.setFromTree(STREAM_METADATA_NAME, root);
        }

        writeHeader(sm.version,
                    sm.logicalScreenWidth,
                    sm.logicalScreenHeight,
                    sm.colorResolution,
                    sm.pixelAspectRatio,
                    sm.backgroundColorIndex,
                    sm.sortFlag,
                    bitsPerPixel,
                    sm.globalColorTable);
    }

    private void writeGraphicControlExtension(int disposalMethod,
                                              boolean userInputFlag,
                                              boolean transparentColorFlag,
                                              int delayTime,
                                              int transparentColorIndex)
      throws IOException {
        try {
            stream.write(0x21);
            stream.write(0xf9);

            stream.write(4);

            int packedFields = (disposalMethod & 0x3) << 2;
            if (userInputFlag) {
                packedFields |= 0x2;
            }
            if (transparentColorFlag) {
                packedFields |= 0x1;
            }
            stream.write(packedFields);

            stream.writeShort((short)delayTime);

            stream.write(transparentColorIndex);
            stream.write(0x00);
        } catch (IOException e) {
            throw new IIOException("I/O error writing Graphic Control Extension!", e);
        }
    }

    private void writeGraphicControlExtension(GIFWritableImageMetadata im)
      throws IOException {
        writeGraphicControlExtension(im.disposalMethod,
                                     im.userInputFlag,
                                     im.transparentColorFlag,
                                     im.delayTime,
                                     im.transparentColorIndex);
    }

    private void writeBlocks(byte[] data) throws IOException {
        if (data != null && data.length > 0) {
            int offset = 0;
            while (offset < data.length) {
                int len = Math.min(data.length - offset, 255);
                stream.write(len);
                stream.write(data, offset, len);
                offset += len;
            }
        }
    }

    private void writePlainTextExtension(GIFWritableImageMetadata im)
      throws IOException {
        if (im.hasPlainTextExtension) {
            try {
                stream.write(0x21);

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