add java classes for handling animated GIF frames retrieval

shamelessly taken from a Stackoverflow post:
http://stackoverflow.com/a/18425922

src/java/clj_image2ascii/java/AnimatedGif.java

@@ -0,0 +1,114 @@
+package clj_image2ascii.java;
+
+import org.w3c.dom.NamedNodeMap;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+
+import javax.imageio.ImageIO;
+import javax.imageio.ImageReader;
+import javax.imageio.metadata.IIOMetadata;
+import javax.imageio.metadata.IIOMetadataNode;
+import javax.imageio.stream.ImageInputStream;
+import java.awt.*;
+import java.awt.image.BufferedImage;
+import java.io.IOException;
+import java.util.ArrayList;
+
+/**
+ * Helper for extracting each frame of animation from a GIF as a separate BufferedImage.
+ * This handles a bunch of edge cases when dealing with different kinds of animated GIFs
+ * such as, getting the proper width/height, handling transparency properly, taking
+ * disposal methods into account, and properly grabbing each frame's delay time before
+ * the next frame should be displayed.
+ * @author SteveH (http://stackoverflow.com/a/18425922)
+ * @author gered (_extremely_ minor tweaks)
+ */
+public class AnimatedGif {
+	public static ImageFrame[] read(ImageInputStream stream) throws IOException {
+		ImageReader reader = ImageIO.getImageReadersByFormatName("gif").next();
+		ArrayList<ImageFrame> frames = new ArrayList<ImageFrame>(2);
+
+		int width = -1;
+		int height = -1;
+
+		IIOMetadata metadata = reader.getStreamMetadata();
+		if (metadata != null) {
+			IIOMetadataNode globalRoot = (IIOMetadataNode) metadata.getAsTree(metadata.getNativeMetadataFormatName());
+
+			NodeList globalScreenDescriptor = globalRoot.getElementsByTagName("LogicalScreenDescriptor");
+
+			if (globalScreenDescriptor != null && globalScreenDescriptor.getLength() > 0) {
+				IIOMetadataNode screenDescriptor = (IIOMetadataNode) globalScreenDescriptor.item(0);
+
+				if (screenDescriptor != null) {
+					width = Integer.parseInt(screenDescriptor.getAttribute("logicalScreenWidth"));
+					height = Integer.parseInt(screenDescriptor.getAttribute("logicalScreenHeight"));
+				}
+			}
+		}
+
+		BufferedImage master = null;
+		Graphics2D masterGraphics = null;
+
+		for (int frameIndex = 0;; frameIndex++) {
+			BufferedImage image;
+			try {
+				image = reader.read(frameIndex);
+			} catch (IndexOutOfBoundsException io) {
+				break;
+			}
+
+			if (width == -1 || height == -1) {
+				width = image.getWidth();
+				height = image.getHeight();
+			}
+
+			IIOMetadataNode root = (IIOMetadataNode) reader.getImageMetadata(frameIndex).getAsTree("javax_imageio_gif_image_1.0");
+			IIOMetadataNode gce = (IIOMetadataNode) root.getElementsByTagName("GraphicControlExtension").item(0);
+			int delay = Integer.valueOf(gce.getAttribute("delayTime"));
+			String disposal = gce.getAttribute("disposalMethod");
+
+			int x = 0;
+			int y = 0;
+
+			if (master == null) {
+				master = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
+				masterGraphics = master.createGraphics();
+				masterGraphics.setBackground(new Color(0, 0, 0, 0));
+			} else {
+				NodeList children = root.getChildNodes();
+				for (int nodeIndex = 0; nodeIndex < children.getLength(); nodeIndex++) {
+					Node nodeItem = children.item(nodeIndex);
+					if (nodeItem.getNodeName().equals("ImageDescriptor")) {
+						NamedNodeMap map = nodeItem.getAttributes();
+						x = Integer.valueOf(map.getNamedItem("imageLeftPosition").getNodeValue());
+						y = Integer.valueOf(map.getNamedItem("imageTopPosition").getNodeValue());
+					}
+				}
+			}
+			masterGraphics.drawImage(image, x, y, null);
+
+			BufferedImage copy = new BufferedImage(master.getColorModel(), master.copyData(null), master.isAlphaPremultiplied(), null);
+			frames.add(new ImageFrame(copy, delay, disposal));
+
+			if (disposal.equals("restoreToPrevious")) {
+				BufferedImage from = null;
+				for (int i = frameIndex - 1; i >= 0; i--) {
+					if (!frames.get(i).disposal.equals("restoreToPrevious") || frameIndex == 0) {
+						from = frames.get(i).image;
+						break;
+					}
+				}
+
+				master = new BufferedImage(from.getColorModel(), from.copyData(null), from.isAlphaPremultiplied(), null);
+				masterGraphics = master.createGraphics();
+				masterGraphics.setBackground(new Color(0, 0, 0, 0));
+			} else if (disposal.equals("restoreToBackgroundColor")) {
+				masterGraphics.clearRect(x, y, image.getWidth(), image.getHeight());
+			}
+		}
+		reader.dispose();
+
+		return frames.toArray(new ImageFrame[frames.size()]);
+	}
+}

src/java/clj_image2ascii/java/ImageFrame.java

@@ -0,0 +1,20 @@
+package clj_image2ascii.java;
+
+import java.awt.image.BufferedImage;
+
+/**
+ * Holds information about a single image frame from an animated GIF.
+ * @author SteveH (http://stackoverflow.com/a/18425922)
+ * @author gered (_extremely_ minor tweaks)
+ */
+public class ImageFrame {
+	public final int delay;
+	public final BufferedImage image;
+	public final String disposal;
+
+	public ImageFrame(BufferedImage image, int delay, String disposal) {
+		this.image = image;
+		this.delay = delay;
+		this.disposal = disposal;
+	}
+}