bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/image/GIFFileFormat.java - platform/eclipse.platform.swt - Git at Google

 package org.eclipse.swt.internal.image;

 /*
  * (c) Copyright IBM Corp. 2000, 2001.
  * All Rights Reserved
  */

 import org.eclipse.swt.*;
 import org.eclipse.swt.graphics.*;
 import java.io.*;

 final class GIFFileFormat extends FileFormat {
 	String signature, version;
 	boolean sorted;
 	int screenWidth, screenHeight, backgroundPixel, aspect, bitsPerPixel;
 	boolean userInput = false;
 	int disposalMethod = 0;
 	int delayTime = 0;
 	int transparentPixel = -1;
 	int repeatCount = 1;

 	static final int GIF_APPLICATION_EXTENSION_BLOCK_ID = 0xFF;
 	static final int GIF_GRAPHICS_CONTROL_BLOCK_ID = 0xF9;
 	static final int GIF_PLAIN_TEXT_BLOCK_ID = 0x01;
 	static final int GIF_COMMENT_BLOCK_ID = 0xFE;
 	static final int GIF_EXTENSION_BLOCK_ID = 0x21;
 	static final int GIF_IMAGE_BLOCK_ID = 0x2C;
 	static final int GIF_TRAILER_ID = 0x3B;

 	/**
 	 * Return whether or not the specified input stream
 	 * represents a GIF file.
 	 */
 	public static boolean isGIFFile(LEDataInputStream stream) {
 		try {
 			byte[] signature = new byte[3];
 			stream.read(signature);
 			stream.unread(signature);
 			return new String(signature).equals("GIF");
 		} catch (Exception e) {
 			return false;
 		}
 	}

 	/**
 	 * Answer a palette containing numGrays
 	 * shades of gray, ranging from black to white.
 	 */
 	static PaletteData grayRamp(int numGrays) {
 		int n = numGrays - 1;
 		RGB[] colors = new RGB[numGrays];
 		for (int i = 0; i < numGrays; i++) {
 			int intensity = (byte)((i * 3) * 256 / n);
 			colors[i] = new RGB(intensity, intensity, intensity);
 		}
 		return new PaletteData(colors);
 	}

 	/**
 	 * Load the GIF image(s) stored in the input stream.
 	 * Return an array of ImageData representing the image(s).
 	 */
 	ImageData[] loadFromByteStream() {
 		byte[] signatureBytes = new byte[3];
 		byte[] versionBytes = new byte[3];
 		byte[] block = new byte[7];
 		try {
 			inputStream.read(signatureBytes);
 			signature = new String(signatureBytes);
 			if (!signature.equals("GIF"))
 				SWT.error(SWT.ERROR_INVALID_IMAGE);

 			inputStream.read(versionBytes);
 			version = new String(versionBytes);

 			inputStream.read(block);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		screenWidth = (block[0] & 0xFF) | ((block[1] & 0xFF) << 8);
 		loader.logicalScreenWidth = screenWidth;
 		screenHeight = (block[2] & 0xFF) | ((block[3] & 0xFF) << 8);
 		loader.logicalScreenHeight = screenHeight;
 		byte bitField = block[4];
 		backgroundPixel = block[5] & 0xFF;
 		aspect = block[6] & 0xFF;
 		bitsPerPixel = ((bitField >> 4) & 0x07) + 1;
 		int depth = (bitField & 0x7) + 1;
 		PaletteData palette = null;
 		if ((bitField & 0x80) != 0) {
 			// Global palette.
 			sorted = (bitField & 0x8) != 0;
 			palette = readPalette(1 << depth);
 		} else {
 			// No global palette.
 			sorted = false;
 			backgroundPixel = -1;
 			depth = bitsPerPixel;
 		}
 		loader.backgroundPixel = backgroundPixel;

 		getExtensions();
 		int id = readID();
 		ImageData[] images = new ImageData[0];
 		while (id == GIF_IMAGE_BLOCK_ID) {
 			ImageData image = readImageBlock(depth, palette);
 			if (loader.hasListeners()) {
 				loader.notifyListeners(new ImageLoaderEvent(loader, image, 3, true));
 			}
 			ImageData[] oldImages = images;
 			images = new ImageData[oldImages.length + 1];
 			System.arraycopy(oldImages, 0, images, 0, oldImages.length);
 			images[images.length - 1] = image;
 			try {
 				/* Read the 0-byte terminator at the end of the image. */
 				id = inputStream.read();
 				if (id > 0) {
 					/* We read the terminator earlier. */
 					inputStream.unread(new byte[] {(byte)id});
 				}
 			} catch (IOException e) {
 				SWT.error(SWT.ERROR_IO, e);
 			}
 			getExtensions();
 			id = readID();
 		}
 		return images;
 	}

 	/**
 	 * Read and return the next block or extension identifier from the file.
 	 */
 	int readID() {
 		try {
 			return inputStream.read();
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		return -1;
 	}

 	/**
 	 * Read extensions until an image descriptor appears.
 	 * In the future, if we care about the extensions, they
 	 * should be properly grouped with the image data before
 	 * which they appeared. Right now, the interesting parts
 	 * of some extensions are kept, but the rest is discarded.
 	 * Throw an error if an error occurs.
 	 */
 	void getExtensions() {
 		int id = readID();
 		while (id != GIF_IMAGE_BLOCK_ID && id != GIF_TRAILER_ID && id > 0) {
 			if (id == GIF_EXTENSION_BLOCK_ID) {
 				readExtension();
 			} else {
 				SWT.error(SWT.ERROR_INVALID_IMAGE);
 			}
 			id = readID();
 		}
 		if (id == GIF_IMAGE_BLOCK_ID || id == GIF_TRAILER_ID) {
 			try {
 				inputStream.unread(new byte[] {(byte)id});
 			} catch (IOException e) {
 				SWT.error(SWT.ERROR_IO, e);
 			}
 		}
 	}

 	/**
 	 * Read a control extension.
 	 * Return the extension block data.
 	 */
 	byte[] readExtension() {
 		int extensionID = readID();
 		if (extensionID == GIF_COMMENT_BLOCK_ID)
 			return readCommentExtension();
 		if (extensionID == GIF_PLAIN_TEXT_BLOCK_ID)
 			return readPlainTextExtension();
 		if (extensionID == GIF_GRAPHICS_CONTROL_BLOCK_ID)
 			return readGraphicsControlExtension();
 		if (extensionID == GIF_APPLICATION_EXTENSION_BLOCK_ID)
 			return readApplicationExtension();
 		// Otherwise, we don't recognize the block. If the
 		// field size is correct, we can just skip over
 		// the block contents.
 		try {
 			int extSize = inputStream.read();
 			if (extSize < 0) {
 				SWT.error(SWT.ERROR_INVALID_IMAGE);
 			}
 			byte[] ext = new byte[extSize];
 			inputStream.read(ext, 0, extSize);
 			return ext;
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 			return null;
 		}
 	}

 	/**
 	 * We have just read the Comment extension identifier
 	 * from the input stream. Read in the rest of the comment
 	 * and return it. GIF comment blocks are variable size.
 	 */
 	byte[] readCommentExtension() {
 		try {
 			byte[] comment = new byte[0];
 			byte[] block = new byte[255];
 			int size = inputStream.read();
 			while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
 				byte[] oldComment = comment;
 				comment = new byte[oldComment.length + size];
 				System.arraycopy(oldComment, 0, comment, 0, oldComment.length);
 				System.arraycopy(block, 0, comment, oldComment.length, size);
 				size = inputStream.read();
 			}
 			return comment;
 		} catch (Exception e) {
 			SWT.error(SWT.ERROR_IO, e);
 			return null;
 		}
 	}

 	/**
 	 * We have just read the PlainText extension identifier
 	 * from the input stream. Read in the plain text info and text,
 	 * and return the text. GIF plain text blocks are variable size.
 	 */
 	byte[] readPlainTextExtension() {
 		try {
 			// Read size of block = 0x0C.
 			inputStream.read();
 			// Read the text information (x, y, width, height, colors).
 			byte[] info = new byte[12];
 			inputStream.read(info);
 			// Read the text.
 			byte[] text = new byte[0];
 			byte[] block = new byte[255];
 			int size = inputStream.read();
 			while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
 				byte[] oldText = text;
 				text = new byte[oldText.length + size];
 				System.arraycopy(oldText, 0, text, 0, oldText.length);
 				System.arraycopy(block, 0, text, oldText.length, size);
 				size = inputStream.read();
 			}
 			return text;
 		} catch (Exception e) {
 			SWT.error(SWT.ERROR_IO, e);
 			return null;
 		}
 	}

 	/**
 	 * We have just read the GraphicsControl extension identifier
 	 * from the input stream. Read in the control information, store
 	 * it, and return it.
 	 */
 	byte[] readGraphicsControlExtension() {
 		try {
 			// Read size of block = 0x04.
 			inputStream.read();
 			// Read the control block.
 			byte[] controlBlock = new byte[4];
 			inputStream.read(controlBlock);
 			byte bitField = controlBlock[0];
 			// Store the user input field.
 			userInput = (bitField & 0x02) != 0;
 			// Store the disposal method.
 			disposalMethod = (bitField >> 2) & 0x07;
 			// Store the delay time.
 			delayTime = (controlBlock[1] & 0xFF) | ((controlBlock[2] & 0xFF) << 8);
 			// Store the transparent color.
 			if ((bitField & 0x01) != 0)
 				transparentPixel = controlBlock[3] & 0xFF;
 			else
 				transparentPixel = -1;
 			// Read block terminator.
 			inputStream.read();
 			return controlBlock;
 		} catch (Exception e) {
 			SWT.error(SWT.ERROR_IO, e);
 			return null;
 		}
 	}

 	/**
 	 * We have just read the Application extension identifier
 	 * from the input stream.  Read in the rest of the extension,
 	 * look for and store 'number of repeats', and return the data.
 	 */
 	byte[] readApplicationExtension() {
 		try {
 			// Read size of block = 0x0B.
 			inputStream.read();
 			// Read application identifier.
 			byte[] applicationBytes = new byte[8];
 			inputStream.read(applicationBytes);
 			String application = new String(applicationBytes);
 			// Read authentication code.
 			byte[] authenticationBytes = new byte[3];
 			inputStream.read(authenticationBytes);
 			String authentication = new String(authenticationBytes);
 			// Read application data.
 			byte[] data = new byte[0];
 			byte[] block = new byte[255];
 			int size = inputStream.read();
 			while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
 				byte[] oldData = data;
 				data = new byte[oldData.length + size];
 				System.arraycopy(oldData, 0, data, 0, oldData.length);
 				System.arraycopy(block, 0, data, oldData.length, size);
 				size = inputStream.read();
 			}
 			// Look for the NETSCAPE 'repeat count' field for an animated GIF.
 			if (application.equals("NETSCAPE") && authentication.equals("2.0") && data[0] == 01) {
 				repeatCount = (data[1] & 0xFF) | ((data[2] & 0xFF) << 8);
 				loader.repeatCount = repeatCount;
 			}
 			return data;
 		} catch (Exception e) {
 			SWT.error(SWT.ERROR_IO, e);
 			return null;
 		}
 	}

 	/**
 	 * Return a DeviceIndependentImage representing the
 	 * image block at the current position in the input stream.
 	 * Throw an error if an error occurs.
 	 */
 	ImageData readImageBlock(int defaultDepth, PaletteData defaultPalette) {
 		int depth;
 		PaletteData palette;
 		byte[] block = new byte[9];
 		try {
 			inputStream.read(block);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		int left = (block[0] & 0xFF) | ((block[1] & 0xFF) << 8);
 		int top = (block[2] & 0xFF) | ((block[3] & 0xFF) << 8);
 		int width = (block[4] & 0xFF) | ((block[5] & 0xFF) << 8);
 		int height = (block[6] & 0xFF) | ((block[7] & 0xFF) << 8);
 		byte bitField = block[8];
 		boolean interlaced = (bitField & 0x40) != 0;
 		boolean sorted = (bitField & 0x20) != 0;
 		if ((bitField & 0x80) != 0) {
 			// Local palette.
 			depth = (bitField & 0x7) + 1;
 			palette = readPalette(1 << depth);
 		} else {
 			// No local palette.
 			depth = defaultDepth;
 			palette = defaultPalette;
 		}
 		// Promote depth to next highest supported value.
 		if (!(depth == 1 || depth == 4 || depth == 8)) {
 			if (depth < 4)
 				depth = 4;
 			else
 				depth = 8;
 		}
 		if (palette == null) {
 			palette = grayRamp(1 << depth);
 		}
 		int initialCodeSize = -1;
 		try {
 			initialCodeSize = inputStream.read();
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		if (initialCodeSize < 0) {
 			SWT.error(SWT.ERROR_INVALID_IMAGE);
 		}
 		ImageData image = ImageData.internal_new(
 			width,
 			height,
 			depth,
 			palette,
 			4,
 			null,
 			0,
 			null,
 			null,
 			-1,
 			transparentPixel,
 			SWT.IMAGE_GIF,
 			left,
 			top,
 			disposalMethod,
 			delayTime);
 		LZWCodec codec = new LZWCodec();
 		codec.decode(inputStream, loader, image, interlaced, initialCodeSize);
 		return image;
 	}

 	/**
 	 * Read a palette from the input stream.
 	 */
 	PaletteData readPalette(int numColors) {
 		byte[] bytes = new byte[numColors * 3];
 		try {
 			if (inputStream.read(bytes) != bytes.length)
 				SWT.error(SWT.ERROR_INVALID_IMAGE);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		RGB[] colors = new RGB[numColors];
 		for (int i = 0; i < numColors; i++)
 			colors[i] = new RGB(bytes[i*3] & 0xFF,
 				bytes[i*3+1] & 0xFF, bytes[i*3+2] & 0xFF);
 		return new PaletteData(colors);
 	}

 	/**
 	 * Write the specified device independent image
 	 * to the output stream.
 	 */
 	void unloadIntoByteStream(ImageData image) {
 		if (!((image.depth == 1) || (image.depth == 4) || (image.depth == 8))) {
 			SWT.error(SWT.ERROR_UNSUPPORTED_DEPTH);
 		}
 		byte bitField = (byte)((0x80 & 0xF8 & 0xF7 & 0x8F) + (image.depth - 1) + ((image.depth - 1) * 16));
 		try {
 			outputStream.write(new byte[] { (byte)'G', (byte)'I', (byte)'F' });
 			outputStream.write(new byte[] { (byte)'8', (byte)'9', (byte)'a' });
 			outputStream.writeShort((short)image.width);
 			outputStream.writeShort((short)image.height);
 			outputStream.writeByte(bitField);
 			outputStream.writeByte((byte)0);
 			outputStream.writeByte((byte)0);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		writePalette(image.palette, image.depth);
 		if (image.transparentPixel != -1 || image.disposalMethod != 0 || image.delayTime != 0) {
 			writeGraphicsControlBlock(image);
 		}
 		writeImageBlock(image);
 	}

 	/**
 	 * Write out a GraphicsControlBlock to describe
 	 * the specified device independent image.
 	 */
 	void writeGraphicsControlBlock(ImageData image) {
 		try {
 			outputStream.write(GIF_EXTENSION_BLOCK_ID);
 			outputStream.write(GIF_GRAPHICS_CONTROL_BLOCK_ID);
 			outputStream.write(0x04); // size of block
 			byte[] gcBlock = new byte[4];
 			gcBlock[0] = (byte)0xFD;
 			gcBlock[1] = 0;
 			gcBlock[2] = 0;
 			gcBlock[3] = 0;
 			if (image.transparentPixel == -1) {
 				gcBlock[0] = (byte)(gcBlock[0] & 0xFE);
 			} else {
 				gcBlock[0] = (byte)(gcBlock[0] | 0x01);
 				gcBlock[3] = (byte)image.transparentPixel;
 			}
 			if (image.disposalMethod != 0) {
 				gcBlock[0] = (byte)(gcBlock[0] | ((image.disposalMethod & 0x07) << 2));
 			}
 			if (image.delayTime != 0) {
 				gcBlock[1] = (byte)(image.delayTime & 0xFF);
 				gcBlock[2] = (byte)((image.delayTime >> 8) & 0xFF);
 			}
 			outputStream.write(gcBlock);
 			outputStream.write(0); // block terminator
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 	}

 	/**
 	 * Write the specified device independent image
 	 * to the current position in the output stream.
 	 */
 	void writeImageBlock(ImageData image) {
 		try {
 			outputStream.write(GIF_IMAGE_BLOCK_ID);
 			byte[] block = new byte[9];
 			block[0] = (byte)(image.x & 0xFF);
 			block[1] = (byte)((image.x >> 8) & 0xFF);
 			block[2] = (byte)(image.y & 0xFF);
 			block[3] = (byte)((image.y >> 8) & 0xFF);
 			block[4] = (byte)(image.width & 0xFF);
 			block[5] = (byte)((image.width >> 8) & 0xFF);
 			block[6] = (byte)(image.height & 0xFF);
 			block[7] = (byte)((image.height >> 8) & 0xFF);
 			block[8] = 0; // no interlace, no sort, no local palette
 			outputStream.write(block);
 			outputStream.write(image.depth);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 		new LZWCodec().encode(outputStream, image);
 	}

 	/**
 	 * Write the specified palette to the output stream.
 	 */
 	void writePalette(PaletteData palette, int depth) {
 		byte[] bytes = new byte[(1 << depth) * 3];
 		int offset = 0;
 		for (int i = 0; i < palette.colors.length; i++) {
 			RGB color = palette.colors[i];
 			bytes[offset] = (byte)color.red;
 			bytes[offset + 1] = (byte)color.green;
 			bytes[offset + 2] = (byte)color.blue;
 			offset += 3;;
 		}
 		try {
 			outputStream.write(bytes);
 		} catch (IOException e) {
 			SWT.error(SWT.ERROR_IO, e);
 		}
 	}
 }
	package org.eclipse.swt.internal.image;

	/*
	* (c) Copyright IBM Corp. 2000, 2001.
	* All Rights Reserved
	*/

	import org.eclipse.swt.*;
	import org.eclipse.swt.graphics.*;
	import java.io.*;

	final class GIFFileFormat extends FileFormat {
	String signature, version;
	boolean sorted;
	int screenWidth, screenHeight, backgroundPixel, aspect, bitsPerPixel;
	boolean userInput = false;
	int disposalMethod = 0;
	int delayTime = 0;
	int transparentPixel = -1;
	int repeatCount = 1;

	static final int GIF_APPLICATION_EXTENSION_BLOCK_ID = 0xFF;
	static final int GIF_GRAPHICS_CONTROL_BLOCK_ID = 0xF9;
	static final int GIF_PLAIN_TEXT_BLOCK_ID = 0x01;
	static final int GIF_COMMENT_BLOCK_ID = 0xFE;
	static final int GIF_EXTENSION_BLOCK_ID = 0x21;
	static final int GIF_IMAGE_BLOCK_ID = 0x2C;
	static final int GIF_TRAILER_ID = 0x3B;

	/**
	* Return whether or not the specified input stream
	* represents a GIF file.
	*/
	public static boolean isGIFFile(LEDataInputStream stream) {
	try {
	byte[] signature = new byte[3];
	stream.read(signature);
	stream.unread(signature);
	return new String(signature).equals("GIF");
	} catch (Exception e) {
	return false;
	}
	}

	/**
	* Answer a palette containing numGrays
	* shades of gray, ranging from black to white.
	*/
	static PaletteData grayRamp(int numGrays) {
	int n = numGrays - 1;
	RGB[] colors = new RGB[numGrays];
	for (int i = 0; i < numGrays; i++) {
	int intensity = (byte)((i * 3) * 256 / n);
	colors[i] = new RGB(intensity, intensity, intensity);
	}
	return new PaletteData(colors);
	}

	/**
	* Load the GIF image(s) stored in the input stream.
	* Return an array of ImageData representing the image(s).
	*/
	ImageData[] loadFromByteStream() {
	byte[] signatureBytes = new byte[3];
	byte[] versionBytes = new byte[3];
	byte[] block = new byte[7];
	try {
	inputStream.read(signatureBytes);
	signature = new String(signatureBytes);
	if (!signature.equals("GIF"))
	SWT.error(SWT.ERROR_INVALID_IMAGE);

	inputStream.read(versionBytes);
	version = new String(versionBytes);

	inputStream.read(block);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	screenWidth = (block[0] & 0xFF) \| ((block[1] & 0xFF) << 8);
	loader.logicalScreenWidth = screenWidth;
	screenHeight = (block[2] & 0xFF) \| ((block[3] & 0xFF) << 8);
	loader.logicalScreenHeight = screenHeight;
	byte bitField = block[4];
	backgroundPixel = block[5] & 0xFF;
	aspect = block[6] & 0xFF;
	bitsPerPixel = ((bitField >> 4) & 0x07) + 1;
	int depth = (bitField & 0x7) + 1;
	PaletteData palette = null;
	if ((bitField & 0x80) != 0) {
	// Global palette.
	sorted = (bitField & 0x8) != 0;
	palette = readPalette(1 << depth);
	} else {
	// No global palette.
	sorted = false;
	backgroundPixel = -1;
	depth = bitsPerPixel;
	}
	loader.backgroundPixel = backgroundPixel;

	getExtensions();
	int id = readID();
	ImageData[] images = new ImageData[0];
	while (id == GIF_IMAGE_BLOCK_ID) {
	ImageData image = readImageBlock(depth, palette);
	if (loader.hasListeners()) {
	loader.notifyListeners(new ImageLoaderEvent(loader, image, 3, true));
	}
	ImageData[] oldImages = images;
	images = new ImageData[oldImages.length + 1];
	System.arraycopy(oldImages, 0, images, 0, oldImages.length);
	images[images.length - 1] = image;
	try {
	/* Read the 0-byte terminator at the end of the image. */
	id = inputStream.read();
	if (id > 0) {
	/* We read the terminator earlier. */
	inputStream.unread(new byte[] {(byte)id});
	}
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	getExtensions();
	id = readID();
	}
	return images;
	}

	/**
	* Read and return the next block or extension identifier from the file.
	*/
	int readID() {
	try {
	return inputStream.read();
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	return -1;
	}

	/**
	* Read extensions until an image descriptor appears.
	* In the future, if we care about the extensions, they
	* should be properly grouped with the image data before
	* which they appeared. Right now, the interesting parts
	* of some extensions are kept, but the rest is discarded.
	* Throw an error if an error occurs.
	*/
	void getExtensions() {
	int id = readID();
	while (id != GIF_IMAGE_BLOCK_ID && id != GIF_TRAILER_ID && id > 0) {
	if (id == GIF_EXTENSION_BLOCK_ID) {
	readExtension();
	} else {
	SWT.error(SWT.ERROR_INVALID_IMAGE);
	}
	id = readID();
	}
	if (id == GIF_IMAGE_BLOCK_ID \|\| id == GIF_TRAILER_ID) {
	try {
	inputStream.unread(new byte[] {(byte)id});
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	}
	}

	/**
	* Read a control extension.
	* Return the extension block data.
	*/
	byte[] readExtension() {
	int extensionID = readID();
	if (extensionID == GIF_COMMENT_BLOCK_ID)
	return readCommentExtension();
	if (extensionID == GIF_PLAIN_TEXT_BLOCK_ID)
	return readPlainTextExtension();
	if (extensionID == GIF_GRAPHICS_CONTROL_BLOCK_ID)
	return readGraphicsControlExtension();
	if (extensionID == GIF_APPLICATION_EXTENSION_BLOCK_ID)
	return readApplicationExtension();
	// Otherwise, we don't recognize the block. If the
	// field size is correct, we can just skip over
	// the block contents.
	try {
	int extSize = inputStream.read();
	if (extSize < 0) {
	SWT.error(SWT.ERROR_INVALID_IMAGE);
	}
	byte[] ext = new byte[extSize];
	inputStream.read(ext, 0, extSize);
	return ext;
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	return null;
	}
	}

	/**
	* We have just read the Comment extension identifier
	* from the input stream. Read in the rest of the comment
	* and return it. GIF comment blocks are variable size.
	*/
	byte[] readCommentExtension() {
	try {
	byte[] comment = new byte[0];
	byte[] block = new byte[255];
	int size = inputStream.read();
	while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
	byte[] oldComment = comment;
	comment = new byte[oldComment.length + size];
	System.arraycopy(oldComment, 0, comment, 0, oldComment.length);
	System.arraycopy(block, 0, comment, oldComment.length, size);
	size = inputStream.read();
	}
	return comment;
	} catch (Exception e) {
	SWT.error(SWT.ERROR_IO, e);
	return null;
	}
	}

	/**
	* We have just read the PlainText extension identifier
	* from the input stream. Read in the plain text info and text,
	* and return the text. GIF plain text blocks are variable size.
	*/
	byte[] readPlainTextExtension() {
	try {
	// Read size of block = 0x0C.
	inputStream.read();
	// Read the text information (x, y, width, height, colors).
	byte[] info = new byte[12];
	inputStream.read(info);
	// Read the text.
	byte[] text = new byte[0];
	byte[] block = new byte[255];
	int size = inputStream.read();
	while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
	byte[] oldText = text;
	text = new byte[oldText.length + size];
	System.arraycopy(oldText, 0, text, 0, oldText.length);
	System.arraycopy(block, 0, text, oldText.length, size);
	size = inputStream.read();
	}
	return text;
	} catch (Exception e) {
	SWT.error(SWT.ERROR_IO, e);
	return null;
	}
	}

	/**
	* We have just read the GraphicsControl extension identifier
	* from the input stream. Read in the control information, store
	* it, and return it.
	*/
	byte[] readGraphicsControlExtension() {
	try {
	// Read size of block = 0x04.
	inputStream.read();
	// Read the control block.
	byte[] controlBlock = new byte[4];
	inputStream.read(controlBlock);
	byte bitField = controlBlock[0];
	// Store the user input field.
	userInput = (bitField & 0x02) != 0;
	// Store the disposal method.
	disposalMethod = (bitField >> 2) & 0x07;
	// Store the delay time.
	delayTime = (controlBlock[1] & 0xFF) \| ((controlBlock[2] & 0xFF) << 8);
	// Store the transparent color.
	if ((bitField & 0x01) != 0)
	transparentPixel = controlBlock[3] & 0xFF;
	else
	transparentPixel = -1;
	// Read block terminator.
	inputStream.read();
	return controlBlock;
	} catch (Exception e) {
	SWT.error(SWT.ERROR_IO, e);
	return null;
	}
	}

	/**
	* We have just read the Application extension identifier
	* from the input stream. Read in the rest of the extension,
	* look for and store 'number of repeats', and return the data.
	*/
	byte[] readApplicationExtension() {
	try {
	// Read size of block = 0x0B.
	inputStream.read();
	// Read application identifier.
	byte[] applicationBytes = new byte[8];
	inputStream.read(applicationBytes);
	String application = new String(applicationBytes);
	// Read authentication code.
	byte[] authenticationBytes = new byte[3];
	inputStream.read(authenticationBytes);
	String authentication = new String(authenticationBytes);
	// Read application data.
	byte[] data = new byte[0];
	byte[] block = new byte[255];
	int size = inputStream.read();
	while ((size > 0) && (inputStream.read(block, 0, size) != -1)) {
	byte[] oldData = data;
	data = new byte[oldData.length + size];
	System.arraycopy(oldData, 0, data, 0, oldData.length);
	System.arraycopy(block, 0, data, oldData.length, size);
	size = inputStream.read();
	}
	// Look for the NETSCAPE 'repeat count' field for an animated GIF.
	if (application.equals("NETSCAPE") && authentication.equals("2.0") && data[0] == 01) {
	repeatCount = (data[1] & 0xFF) \| ((data[2] & 0xFF) << 8);
	loader.repeatCount = repeatCount;
	}
	return data;
	} catch (Exception e) {
	SWT.error(SWT.ERROR_IO, e);
	return null;
	}
	}

	/**
	* Return a DeviceIndependentImage representing the
	* image block at the current position in the input stream.
	* Throw an error if an error occurs.
	*/
	ImageData readImageBlock(int defaultDepth, PaletteData defaultPalette) {
	int depth;
	PaletteData palette;
	byte[] block = new byte[9];
	try {
	inputStream.read(block);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	int left = (block[0] & 0xFF) \| ((block[1] & 0xFF) << 8);
	int top = (block[2] & 0xFF) \| ((block[3] & 0xFF) << 8);
	int width = (block[4] & 0xFF) \| ((block[5] & 0xFF) << 8);
	int height = (block[6] & 0xFF) \| ((block[7] & 0xFF) << 8);
	byte bitField = block[8];
	boolean interlaced = (bitField & 0x40) != 0;
	boolean sorted = (bitField & 0x20) != 0;
	if ((bitField & 0x80) != 0) {
	// Local palette.
	depth = (bitField & 0x7) + 1;
	palette = readPalette(1 << depth);
	} else {
	// No local palette.
	depth = defaultDepth;
	palette = defaultPalette;
	}
	// Promote depth to next highest supported value.
	if (!(depth == 1 \|\| depth == 4 \|\| depth == 8)) {
	if (depth < 4)
	depth = 4;
	else
	depth = 8;
	}
	if (palette == null) {
	palette = grayRamp(1 << depth);
	}
	int initialCodeSize = -1;
	try {
	initialCodeSize = inputStream.read();
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	if (initialCodeSize < 0) {
	SWT.error(SWT.ERROR_INVALID_IMAGE);
	}
	ImageData image = ImageData.internal_new(
	width,
	height,
	depth,
	palette,
	4,
	null,
	0,
	null,
	null,
	-1,
	transparentPixel,
	SWT.IMAGE_GIF,
	left,
	top,
	disposalMethod,
	delayTime);
	LZWCodec codec = new LZWCodec();
	codec.decode(inputStream, loader, image, interlaced, initialCodeSize);
	return image;
	}

	/**
	* Read a palette from the input stream.
	*/
	PaletteData readPalette(int numColors) {
	byte[] bytes = new byte[numColors * 3];
	try {
	if (inputStream.read(bytes) != bytes.length)
	SWT.error(SWT.ERROR_INVALID_IMAGE);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	RGB[] colors = new RGB[numColors];
	for (int i = 0; i < numColors; i++)
	colors[i] = new RGB(bytes[i*3] & 0xFF,
	bytes[i3+1] & 0xFF, bytes[i3+2] & 0xFF);
	return new PaletteData(colors);
	}

	/**
	* Write the specified device independent image
	* to the output stream.
	*/
	void unloadIntoByteStream(ImageData image) {
	if (!((image.depth == 1) \|\| (image.depth == 4) \|\| (image.depth == 8))) {
	SWT.error(SWT.ERROR_UNSUPPORTED_DEPTH);
	}
	byte bitField = (byte)((0x80 & 0xF8 & 0xF7 & 0x8F) + (image.depth - 1) + ((image.depth - 1) * 16));
	try {
	outputStream.write(new byte[] { (byte)'G', (byte)'I', (byte)'F' });
	outputStream.write(new byte[] { (byte)'8', (byte)'9', (byte)'a' });
	outputStream.writeShort((short)image.width);
	outputStream.writeShort((short)image.height);
	outputStream.writeByte(bitField);
	outputStream.writeByte((byte)0);
	outputStream.writeByte((byte)0);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	writePalette(image.palette, image.depth);
	if (image.transparentPixel != -1 \|\| image.disposalMethod != 0 \|\| image.delayTime != 0) {
	writeGraphicsControlBlock(image);
	}
	writeImageBlock(image);
	}

	/**
	* Write out a GraphicsControlBlock to describe
	* the specified device independent image.
	*/
	void writeGraphicsControlBlock(ImageData image) {
	try {
	outputStream.write(GIF_EXTENSION_BLOCK_ID);
	outputStream.write(GIF_GRAPHICS_CONTROL_BLOCK_ID);
	outputStream.write(0x04); // size of block
	byte[] gcBlock = new byte[4];
	gcBlock[0] = (byte)0xFD;
	gcBlock[1] = 0;
	gcBlock[2] = 0;
	gcBlock[3] = 0;
	if (image.transparentPixel == -1) {
	gcBlock[0] = (byte)(gcBlock[0] & 0xFE);
	} else {
	gcBlock[0] = (byte)(gcBlock[0] \| 0x01);
	gcBlock[3] = (byte)image.transparentPixel;
	}
	if (image.disposalMethod != 0) {
	gcBlock[0] = (byte)(gcBlock[0] \| ((image.disposalMethod & 0x07) << 2));
	}
	if (image.delayTime != 0) {
	gcBlock[1] = (byte)(image.delayTime & 0xFF);
	gcBlock[2] = (byte)((image.delayTime >> 8) & 0xFF);
	}
	outputStream.write(gcBlock);
	outputStream.write(0); // block terminator
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	}

	/**
	* Write the specified device independent image
	* to the current position in the output stream.
	*/
	void writeImageBlock(ImageData image) {
	try {
	outputStream.write(GIF_IMAGE_BLOCK_ID);
	byte[] block = new byte[9];
	block[0] = (byte)(image.x & 0xFF);
	block[1] = (byte)((image.x >> 8) & 0xFF);
	block[2] = (byte)(image.y & 0xFF);
	block[3] = (byte)((image.y >> 8) & 0xFF);
	block[4] = (byte)(image.width & 0xFF);
	block[5] = (byte)((image.width >> 8) & 0xFF);
	block[6] = (byte)(image.height & 0xFF);
	block[7] = (byte)((image.height >> 8) & 0xFF);
	block[8] = 0; // no interlace, no sort, no local palette
	outputStream.write(block);
	outputStream.write(image.depth);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	new LZWCodec().encode(outputStream, image);
	}

	/**
	* Write the specified palette to the output stream.
	*/
	void writePalette(PaletteData palette, int depth) {
	byte[] bytes = new byte[(1 << depth) * 3];
	int offset = 0;
	for (int i = 0; i < palette.colors.length; i++) {
	RGB color = palette.colors[i];
	bytes[offset] = (byte)color.red;
	bytes[offset + 1] = (byte)color.green;
	bytes[offset + 2] = (byte)color.blue;
	offset += 3;;
	}
	try {
	outputStream.write(bytes);
	} catch (IOException e) {
	SWT.error(SWT.ERROR_IO, e);
	}
	}
	}