giffileformat.java

源码为Eclipse开源开发平台桌面开发工具SWT的源代码,

			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) {
				int colorIndex = controlBlock[3] & 0xFF;
				/* Work around: a customer has a GIF that specifies an
				 * invalid color index that is larger than the number
				 * of entries in the palette. Detect this case, and
				 * ignore the specified color index. */
				if (colorIndex <= 1 << defaultDepth) {
					transparentPixel = colorIndex;
				}
			} 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) { //$NON-NLS-1$ //$NON-NLS-2$
				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(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);
		try {
			outputStream.write(0x3B);
		} catch (IOException e) {
			SWT.error(SWT.ERROR_IO, e);
		}
	}

	/**
	 * 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);
		}
	}
}