GIF是一种图像文件格式，可以将多幅图像保存到一个文件中，形成动画。网上常见的动画文件都是GIF文件格式。适当地使用动画，可以使我们的网站或应用显得更加活泼，从而更具有吸引力。
通过开发应用，我们可以根据自己的需要，定制实现GIF动画的生成方式，本文提供一个GIF编码类，通过将该类嵌入您的应用中，轻松几部就可以实现GIF动画的生成。
使用方式
我们先看看如何使用
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
public class GifEncoderTest {
public static void main(String[] argv) throws Exception {
BufferedImage[] imgs = new BufferedImage[4];
imgs[0] = ImageIO.read(new File("a1.png"));
imgs[1] = ImageIO.read(new File("a2.jpg"));
imgs[2] = ImageIO.read(new File("a3.jpg"));
imgs[3] = ImageIO.read(new File("a4.jpg"));
GifEncoder gif = new GifEncoder(300, 200, new java.io.FileOutputStream("D:\\eclipse-workspace\\image-toolkit\\images\\bbbb.gif"), true, true);
for (BufferedImage img : imgs) {
gif.addImage(img);
}
gif.setDelay(100); //帧之间的延时，单位毫秒
gif.encodeMultiple();
}
}
其中GifEncoder就是我们需要使用的类，通过给该类添加图片，设置延时，就可以生成我么需要的动画。
GifEncoder构造函数的参数如下：
GifEncoder(int width, int height, OutputStream out, boolean interlace)
Width：最终生成的图片的宽度
Height：最终生成的图片的高度
Out: 输出流
Interlace: 是否采用交错编码方式
GIF编码类实现方式
GIF编码包含四个文件Pixel.java，IntHashtable.java，TrueTo256.java和GifEncoder.java
Pixel.java 实现单点的颜色值的设置或读取
IntHashtable.java 实现整型数据哈希表的操作
TrueTo256.java 实现真彩色到256色的转换
GifEncoder.java 实现Gif文件编码
Pixel.java代码
import java.awt.image.*;
public class Pixel {
public int red;
public int green;
public int blue;
public int alpha=0xFF;
public double hue;
public double saturation;
public double luminosity;
private int rgb;
public Pixel() {
}
public void setRGB(int rgb) {
red = (rgb & 0x00FF0000) / 0x00010000;
green = (rgb & 0x0000FF00) / 0x00000100;
blue = rgb & 0x000000FF;
alpha = (rgb >> 24)&0x0ff;
this.rgb = rgb;
}
public int getRGB() {
rgb = alpha<<24 | 0x00010000 * red | 0x00000100 * green | blue;
return this.rgb;
}
public static void setRgb(BufferedImage image, int x, int y, int red, int green, int blue) {
int rgb = 0xFF000000 | red * 0x00010000 | green * 0x00000100 | blue;
image.setRGB(x, y, rgb);
}
public static int pixelIntensity(int rgb) {
int red = (rgb&0x00FF0000)/0x00010000;
int green = (rgb&0x0000FF00)/0x00000100;
int blue = rgb&0x000000FF;
return (int) (0.299 * red + 0.587 * green + 0.114 * blue + 0.5);
}
}
IntHashtable.java 代码
import java.util.*;
public class IntHashtable extends Dictionary implements Cloneable {
/// The hash table data.
private IntHashtableEntry table[];
/// The total number of entries in the hash table.
private int count;
/// Rehashes the table when count exceeds this threshold.
private int threshold;
/// The load factor for the hashtable.
private float loadFactor;
public IntHashtable(int initialCapacity, float loadFactor) {
if (initialCapacity <= 0 || loadFactor <= 0.0)
throw new IllegalArgumentException();
this.loadFactor = loadFactor;
table = new IntHashtableEntry[initialCapacity];
threshold = (int) (initialCapacity * loadFactor);
}
public IntHashtable(int initialCapacity) {
this(initialCapacity, 0.75f);
}
public IntHashtable() {
this(101, 0.75f);
}
public int size() {
return count;
}
public boolean isEmpty() {
return count == 0;
}
public synchronized Enumeration keys() {
return new IntHashtableEnumerator(table, true);
}
public synchronized Enumeration elements() {
return new IntHashtableEnumerator(table, false);
}
public synchronized boolean contains(Object value) {
if (value == null)
throw new NullPointerException();
IntHashtableEntry tab[] = table;
for (int i = tab.length; i-- > 0;) {
for (IntHashtableEntry e = tab[i]; e != null; e = e.next) {
if (e.value.equals(value))
return true;
}
}
return false;
}
public synchronized boolean containsKey(int key) {
IntHashtableEntry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
if (e.hash == hash && e.key == key)
return true;
}
return false;
}
public synchronized Object get(int key) {
IntHashtableEntry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
if (e.hash == hash && e.key == key)
return e.value;
}
return null;
}
public Object get(Object okey) {
if (!(okey instanceof Integer))
throw new InternalError("key is not an Integer");
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return get(key);
}
protected void rehash() {
int oldCapacity = table.length;
IntHashtableEntry oldTable[] = table;
int newCapacity = oldCapacity * 2 + 1;
IntHashtableEntry newTable[] = new IntHashtableEntry[newCapacity];
threshold = (int) (newCapacity * loadFactor);
table = newTable;
for (int i = oldCapacity; i-- > 0;) {
for (IntHashtableEntry old = oldTable[i]; old != null;) {
IntHashtableEntry e = old;
old = old.next;
int index = (e.hash & 0x7FFFFFFF) % newCapacity;
e.next = newTable[index];
newTable[index] = e;
}
}
}
public synchronized Object put(int key, Object value) {
// Make sure the value is not null.
if (value == null)
throw new NullPointerException();
// Makes sure the key is not already in the hashtable.
IntHashtableEntry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (IntHashtableEntry e = tab[index]; e != null; e = e.next) {
if (e.hash == hash && e.key == key) {
Object old = e.value;
e.value = value;
return old;
}
}
if (count >= threshold) {
// Rehash the table if the threshold is exceeded.
rehash();
return put(key, value);
}
// Creates the new entry.
IntHashtableEntry e = new IntHashtableEntry();
e.hash = hash;
e.key = key;
e.value = value;
e.next = tab[index];
tab[index] = e;
++count;
return null;
}
public Object put(Object okey, Object value) {
if (!(okey instanceof Integer))
throw new InternalError("key is not an Integer");
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return put(key, value);
}
public synchronized Object remove(int key) {
IntHashtableEntry tab[] = table;
int hash = key;
int index = (hash & 0x7FFFFFFF) % tab.length;
for (IntHashtableEntry e = tab[index], prev = null; e != null; prev = e, e = e.next) {
if (e.hash == hash && e.key == key) {
if (prev != null)
prev.next = e.next;
else
tab[index] = e.next;
--count;
return e.value;
}
}
return null;
}
public Object remove(Object okey) {
if (!(okey instanceof Integer))
throw new InternalError("key is not an Integer");
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return remove(key);
}
public synchronized void clear() {
IntHashtableEntry tab[] = table;
for (int index = tab.length; --index >= 0;)
tab[index] = null;
count = 0;
}
public synchronized Object clone() {
try {
IntHashtable t = (IntHashtable) super.clone();
t.table = new IntHashtableEntry[table.length];
for (int i = table.length; i-- > 0;)
t.table[i] = (table[i] != null) ? (IntHashtableEntry) table[i].clone() : null;
return t;
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
public synchronized String toString() {
int max = size() - 1;
StringBuffer buf = new StringBuffer();
Enumeration k = keys();
Enumeration e = elements();
buf.append("{");
for (int i = 0; i <= max; ++i) {
String s1 = k.nextElement().toString();
String s2 = e.nextElement().toString();
buf.append(s1 + "=" + s2);
if (i < max)
buf.append(", ");
}
buf.append("}");
return buf.toString();
}
}
class IntHashtableEntry {
int hash;
int key;
Object value;
IntHashtableEntry next;
protected Object clone() {
IntHashtableEntry entry = new IntHashtableEntry();
entry.hash = hash;
entry.key = key;
entry.value = value;
entry.next = (next != null) ? (IntHashtableEntry) next.clone() : null;
return entry;
}
}
class IntHashtableEnumerator implements Enumeration {
boolean keys;
int index;
IntHashtableEntry table[];
IntHashtableEntry entry;
IntHashtableEnumerator(IntHashtableEntry table[], boolean keys) {
this.table = table;
this.keys = keys;
this.index = table.length;
}
public boolean hasMoreElements() {
if (entry != null)
return true;
while (index-- > 0)
if ((entry = table[index]) != null)
return true;
return false;
}
public Object nextElement() {
if (entry == null)
while ((index-- > 0) && ((entry = table[index]) == null))
;
if (entry != null) {
IntHashtableEntry e = entry;
entry = e.next;
return keys ? new Integer(e.key) : e.value;
}
throw new NoSuchElementException("IntHashtableEnumerator");
}
}
TrueTo256.java 代码
import java.awt.image.BufferedImage;
public class TrueTo256 {
public static int colorTransfer(int rgb) {
int r = (rgb&0x0F00000)>>20;
int g = (rgb&0x000F000)>>12;
int b = (rgb&0x00000F0)>>4;
return (r<<8|g<<4|b);
}
public static int colorRevert(int rgb) {
int r = (rgb&0x0F00)<<12;
int g = (rgb&0x000F0)<<8;
int b = (rgb&0x00000F)<<4;
return (r|g|b);
}
private static int getDouble(int a, int b) {
int red = ((a&0x0F00)>>8) - ((b&0x0F00)>>8);
int grn = ((a&0x00F0)>>4) - ((b&0x00F0)>>4);
int blu = (a&0x000F) - (b&0x000F);
return red*red + blu*blu + grn*grn;
}
public static int getSimulatorColor(int rgb, int[] rgbs, int m) {
int r = 0;
int lest = getDouble(rgb, rgbs[r]);
for (int i=1; i < m; i++) {
int d2 = getDouble(rgb, rgbs[i]);
if (lest > d2) {
lest = d2;
r = i;
}
}
return rgbs[r];
}
public static void transferTo256(int[][] rgbs) {
int n = 4096;
int m = 256;
int[] colorV = new int[n];
int[] colorIndex = new int[n];
//初始化
for (int i=0; i < n; i++) {
colorV[i] = 0;
colorIndex[i] = i;
}
//颜色转换
for (int x = 0; x < rgbs.length; x++) {
for (int y = 0; y < rgbs[x].length; y++) {
rgbs[x][y] = colorTransfer(rgbs[x][y]);
colorV[rgbs[x][y]]++;
}
}
//出现频率排序
boolean exchange;
int r;
for (int i=0; i < n; i++) {
exchange = false;
for (int j=n-2; j>=i; j--) {
if (colorV[colorIndex[j+1]] > colorV[colorIndex[j]]) {
r = colorIndex[j];
colorIndex[j] = colorIndex[j+1];
colorIndex[j+1] = r;
exchange = true;
}
}
if (!exchange) break;
}
//颜色排序位置
for (int i=0; i < n; i++) {
colorV[colorIndex[i]] = i;
}
for (int x = 0; x < rgbs.length; x++) {
for (int y = 0; y < rgbs[x].length; y++) {
if (colorV[rgbs[x][y]] >= m) {
rgbs[x][y] = colorRevert(getSimulatorColor(rgbs[x][y], colorIndex, m));
} else {
rgbs[x][y] = colorRevert(rgbs[x][y]);
}
}
}
}
public static void transferToRed(int[][] rgbs) {
for (int x = 0; x < rgbs.length; x++) {
for (int y = 0; y < rgbs[x].length; y++) {
rgbs[x][y] = rgbs[x][y]&0x00FF0000;
}
}
}
public static void transferToGreen(int[][] rgbs) {
for (int x = 0; x < rgbs.length; x++) {
for (int y = 0; y < rgbs[x].length; y++) {
rgbs[x][y] = rgbs[x][y]&0x00FF00;
}
}
}
public static void transferToBlue(int[][] rgbs) {
for (int x = 0; x < rgbs.length; x++) {
for (int y = 0; y < rgbs[x].length; y++) {
rgbs[x][y] = rgbs[x][y]&0x00FF;
}
}
}
public static BufferedImage trueTo256(BufferedImage img) {
int[][] rgbs = new int[img.getWidth()][img.getHeight()];
BufferedImage cloneImg = new BufferedImage(img.getWidth(), img.getHeight(),
BufferedImage.TYPE_INT_RGB);
for (int x=0; x < rgbs.length; x++) {
for (int y=0; y < rgbs[x].length; y++) {
rgbs[x][y] = img.getRGB(x, y);
}
}
transferTo256(rgbs);
for (int x=0; x < rgbs.length; x++) {
for (int y=0; y < rgbs[x].length; y++) {
cloneImg.setRGB(x, y, rgbs[x][y]);
}
}
return cloneImg;
}
}
GifEncoder.java 代码
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Enumeration;
public class GifEncoder {
private int width, height;
private int[][] rgbPixels;
private IntHashtable colorHash;
private boolean interlace = false;
private OutputStream out;
private int sec = 50;
private ArrayList images = new ArrayList();
private boolean _init = false;
private int count = 0;
int Width, Height;
boolean Interlace;
int curx, cury;
int CountDown;
int Pass = 0;
class GifEncoderHashitem {
public int rgb;
public int count;
public int index;
public boolean isTransparent;
public GifEncoderHashitem(int rgb, int count, int index, boolean isTransparent) {
this.rgb = rgb;
this.count = count;
this.index = index;
this.isTransparent = isTransparent;
}
}
public GifEncoder() {
}
public int getDelay() {
return sec;
}
public int getCount() {
return count;
}
public ArrayList getImages() {
return images;
}
public int getWidth() {
return width;
}
public int getHeight() {
return height;
}
public void init(int width, int height, OutputStream out, boolean interlace) throws IOException {
this.out = out;
this.interlace = interlace;
this.width = width;
this.height = height;
this.Interlace = interlace;
this.Width = width;
this.Height = height;
_init = true;
}
public GifEncoder(int width, int height, OutputStream out, boolean interlace) throws IOException {
this.out = out;
this.interlace = interlace;
this.width = width;
this.height = height;
this.Interlace = interlace;
this.Width = width;
this.Height = height;
_init = true;
}
public boolean isInit() {
return this._init;
}
public void clearImage() {
images.clear();
this._init = false;
}
public void setOutputStream(OutputStream out) {
this.out = out;
}
public void setDelay(int millisecond) {
this.sec = millisecond/10;
}
public void setCount(int count) {
this.count = count;
}
public BufferedImage scaleTo(BufferedImage image, int width, int height) {
int pwidth = image.getWidth();
int pheight = image.getHeight();
BufferedImage bimg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = bimg.createGraphics();
g2d.drawImage(image, 0, 0, width, height, 0, 0, pwidth, pheight, null);
return bimg;
}
public void addImage(BufferedImage img) {
if (img.getWidth() != width || img.getHeight() != height) {
img = scaleTo(img, width, height);
}
images.add(TrueTo256.trueTo256(img));
}
public void encodeMultiple() throws IOException {
encodeMultiple(images);
}
void GIFEncodeHeader(OutputStream outs, byte Background) throws IOException {
// Write the Magic header
writeString(outs, "GIF89a");
// Write out the screen width and height
Putword(Width, outs);
Putword(Height, outs);
// Indicate that there is a global colour map
byte B = (byte) 0x00; // Yes, there is a color map
// OR in the resolution
B |= (byte) ((8 - 1) << 4);
// Not sorted
// OR in the Bits per Pixel
B |= (byte) ((8 - 1));
// Write it out
Putbyte(B, outs);
// Write out the Background colour
Putbyte(Background, outs);
// Pixel aspect ratio - 1:1.
// Putbyte( (byte) 49, outs );
// Java's GIF reader currently has a bug, if the aspect ratio byte is
// not zero it throws an ImageFormatException. It doesn't know that
// 49 means a 1:1 aspect ratio. Well, whatever, zero works with all
// the other decoders I've tried so it probably doesn't hurt.
Putbyte((byte) 0, outs);
}
void GIFAppControl(OutputStream outs, int count) throws IOException {
Putbyte((byte) 0x21, outs);
Putbyte((byte) 0xff, outs);
Putbyte((byte) 0x0b, outs);
writeString(outs, "NETSCAPE2.0");
Putbyte((byte) 0x03, outs);
Putbyte((byte) 0x01, outs);
Putbyte((byte) (0x00ff & count), outs);
Putbyte((byte) (0xff00 & (count >> 4)), outs);
Putbyte((byte) 0x00, outs);
}
void gifControl(OutputStream outs, int sec) throws IOException {
Putbyte((byte) 0x21, outs);
Putbyte((byte) 0xf9, outs);
Putbyte((byte) 0x04, outs);
Putbyte((byte) 0x08, outs);
Putbyte((byte) (sec & 0x0ff), outs);
Putbyte((byte) ((sec & 0x0ff00) >> 8), outs);
Putbyte((byte) 0x40, outs);
Putbyte((byte) 0, outs);
}
void gifEncodeBody(OutputStream outs, int Width, int Height, boolean Interlace, byte Background, int Transparent,
int BitsPerPixel, byte[] Red, byte[] Green, byte[] Blue) throws IOException {
int LeftOfs, TopOfs;
int InitCodeSize;
LeftOfs = TopOfs = 0;
// The initial code size
if (BitsPerPixel <= 1)
InitCodeSize = 2;
else
InitCodeSize = BitsPerPixel;
if (sec > 0) {
gifControl(outs, sec);
}
// Write an Image separator
Putbyte((byte) ',', outs);
// Write the Image header
Putword(LeftOfs, outs);
Putword(TopOfs, outs);
Putword(Width, outs);
Putword(Height, outs);
// Write out whether or not the image is interlaced
// Indicate that there is a global colour map
byte B = (byte) 0x80; // Yes, there is a color map
// OR in the resolution
B |= (byte) ((8 - 1) << 4);
// Not sorted
// OR in the Bits per Pixel
B |= (byte) ((BitsPerPixel - 1));
// Write it out
Putbyte(B, outs);
int ColorMapSize = 1 << BitsPerPixel;
for (int i = 0; i < ColorMapSize; ++i) {
Putbyte(Red[i], outs);
Putbyte(Green[i], outs);
Putbyte(Blue[i], outs);
}
// Write out extension for transparent colour index, if necessary.
if (Transparent != -1) {
Putbyte((byte) '!', outs);
Putbyte((byte) 0xf9, outs);
Putbyte((byte) 4, outs);
Putbyte((byte) 0x0d, outs);
Putbyte((byte) 0, outs);
Putbyte((byte) 0, outs);
Putbyte((byte) Transparent, outs);
Putbyte((byte) 0, outs);
}
// Write out the initial code size
Putbyte((byte) InitCodeSize, outs);
// Go and actually compress the data
compress(InitCodeSize + 1, outs);
// Write out a Zero-length packet (to end the series)
Putbyte((byte) 0, outs);
}
void GIFEncodeBottom(OutputStream outs) throws IOException {
// Write the GIF file terminator
Putbyte((byte) ';', outs);
}
private void encodeMultiple(ArrayList imgs) throws IOException {
if (imgs.size() == 0)
return;
encodeHeader();
for (int i = 0; i < imgs.size(); i++) {
encodeInit((BufferedImage) imgs.get(i));
encodeSingle();
}
GIFEncodeBottom(out);
}
public void encodeMultiple2(ArrayList imgs) throws IOException {
if (imgs.size() == 0)
return;
BufferedImage tmp = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = tmp.createGraphics();
encodeHeader();
for (int i = 0; i < imgs.size(); i++) {
g2d.drawImage((BufferedImage) imgs.get(i), 0, 0, width, height, null);
encodeInit(tmp);
encodeSingle();
}
g2d.dispose();
GIFEncodeBottom(out);
}
public void encodeMultiple(BufferedImage[] imgs) throws IOException {
if (imgs.length == 0)
return;
encodeHeader();
for (int i = 0; i < imgs.length; i++) {
encodeInit(imgs[i]);
encodeSingle();
}
GIFEncodeBottom(out);
}
public void encodeMultiple2(BufferedImage[] imgs) throws IOException {
if (imgs.length == 0)
return;
BufferedImage tmp = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = tmp.createGraphics();
encodeHeader();
for (int i = 0; i < imgs.length; i++) {
g2d.drawImage(imgs[i], 0, 0, width, height, null);
encodeInit(tmp);
encodeSingle();
}
g2d.dispose();
GIFEncodeBottom(out);
}
void encodeInit(BufferedImage img) throws IOException {
cur_accum = 0;
cur_bits = 0;
Pass = 0;
curx = 0;
cury = 0;
this.Interlace = true;
CountDown = Width * Height;
rgbPixels = new int[height][width];
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
rgbPixels[y][x] = img.getRGB(x, y);
}
}
}
void encodeHeader() throws IOException {
GIFEncodeHeader(out, (byte) 0);
GIFAppControl(out, count);
}
void encodeSingle() throws IOException {
int transparentIndex = -1;
int transparentRgb = -1;
colorHash = new IntHashtable();
int index = 0;
for (int row = 0; row < height; ++row) {
int rowOffset = row * width;
for (int col = 0; col < width; ++col) {
int rgb = rgbPixels[row][col];
boolean isTransparent = ((rgb >>> 24) < 0x80);
Pixel pixel = new Pixel();
pixel.setRGB(rgb);
/***
* int red = pixel.red/32; int green = pixel.green/16; int blue = pixel.blue/16;
* rgb = red * 32 | green * 5 | blue;
**/
if (isTransparent) {
if (transparentIndex < 0) {
transparentIndex = index;
transparentRgb = rgb;
} else if (rgb != transparentRgb) {
rgbPixels[row][col] = rgb = transparentRgb;
}
}
rgbPixels[row][col] = rgb;
GifEncoderHashitem item = (GifEncoderHashitem) colorHash.get(rgb);
if (item == null) {
if (index >= 256)
throw new IOException("too many colors for a GIF");
item = new GifEncoderHashitem(pixel.getRGB(), 1, index, isTransparent);
++index;
colorHash.put(rgb, item);
} else
++item.count;
}
}
int logColors;
if (index <= 2)
logColors = 1;
else if (index <= 4)
logColors = 2;
else if (index <= 16)
logColors = 4;
else
logColors = 8;
int mapSize = 1 << logColors;
byte[] reds = new byte[mapSize];
byte[] grns = new byte[mapSize];
byte[] blus = new byte[mapSize];
for (Enumeration e = colorHash.elements(); e.hasMoreElements();) {
GifEncoderHashitem item = (GifEncoderHashitem) e.nextElement();
reds[item.index] = (byte) ((item.rgb >> 16) & 0xff);
grns[item.index] = (byte) ((item.rgb >> 8) & 0xff);
blus[item.index] = (byte) (item.rgb & 0xff);
}
gifEncodeBody(out, width, height, interlace, (byte) 0, transparentIndex, logColors, reds, grns, blus);
}
byte GetPixel(int x, int y) throws IOException {
GifEncoderHashitem item = (GifEncoderHashitem) colorHash.get(rgbPixels[y][x]);
if (item == null)
throw new IOException("color not found");
return (byte) item.index;
}
static void writeString(OutputStream out, String str) throws IOException {
byte[] buf = str.getBytes();
out.write(buf);
}
// Adapted from ppmtogif, which is based on GIFENCOD by David
// Rowley <mgardi@watdscu.waterloo.edu>. Lempel-Zim compression
// based on "compress".
// Bump the 'curx' and 'cury' to point to the next pixel
void BumpPixel() {
// Bump the current X position
++curx;
// If we are at the end of a scan line, set curx back to the beginning
// If we are interlaced, bump the cury to the appropriate spot,
// otherwise, just increment it.
if (curx == Width) {
curx = 0;
if (!Interlace)
++cury;
else {
switch (Pass) {
case 0:
cury += 8;
if (cury >= Height) {
++Pass;
cury = 4;
}
break;
case 1:
cury += 8;
if (cury >= Height) {
++Pass;
cury = 2;
}
break;
case 2:
cury += 4;
if (cury >= Height) {
++Pass;
cury = 1;
}
break;
case 3:
cury += 2;
break;
}
}
}
}
static final int EOF = -1;
// Return the next pixel from the image
int GIFNextPixel() throws IOException {
byte r;
if (CountDown == 0)
return EOF;
--CountDown;
r = GetPixel(curx, cury);
BumpPixel();
return r & 0xff;
}
// Write out a word to the GIF file
void Putword(int w, OutputStream outs) throws IOException {
Putbyte((byte) (w & 0xff), outs);
Putbyte((byte) ((w >> 8) & 0xff), outs);
}
// Write out a byte to the GIF file
void Putbyte(byte b, OutputStream outs) throws IOException {
outs.write(b);
}
// GIFCOMPR.C - GIF Image compression routines
//
// Lempel-Ziv compression based on 'compress'. GIF modifications by
// David Rowley (mgardi@watdcsu.waterloo.edu)
// General DEFINEs
static final int BITS = 12;
static final int HSIZE = 5003; // 80% occupancy
// GIF Image compression - modified 'compress'
//
// Based on: compress.c - File compression ala IEEE Computer, June 1984.
//
// By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
// Jim McKie (decvax!mcvax!jim)
// Steve Davies (decvax!vax135!petsd!peora!srd)
// Ken Turkowski (decvax!decwrl!turtlevax!ken)
// James A. Woods (decvax!ihnp4!ames!jaw)
// Joe Orost (decvax!vax135!petsd!joe)
int n_bits; // number of bits/code
int maxbits = BITS; // user settable max # bits/code
int maxcode; // maximum code, given n_bits
int maxmaxcode = 1 << BITS; // should NEVER generate this code
final int MAXCODE(int n_bits) {
return (1 << n_bits) - 1;
}
int[] htab = new int[HSIZE];
int[] codetab = new int[HSIZE];
int hsize = HSIZE; // for dynamic table sizing
int free_ent = 0; // first unused entry
// block compression parameters -- after all codes are used up,
// and compression rate changes, start over.
boolean clear_flg = false;
// Algorithm: use open addressing double hashing (no chaining) on the
// prefix code / next character combination. We do a variant of Knuth's
// algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
// secondary probe. Here, the modular division first probe is gives way
// to a faster exclusive-or manipulation. Also do block compression with
// an adaptive reset, whereby the code table is cleared when the compression
// ratio decreases, but after the table fills. The variable-length output
// codes are re-sized at this point, and a special CLEAR code is generated
// for the decompressor. Late addition: construct the table according to
// file size for noticeable speed improvement on small files. Please direct
// questions about this implementation to ames!jaw.
int g_init_bits;
int ClearCode;
int EOFCode;
void compress(int init_bits, OutputStream outs) throws IOException {
int fcode;
int i /* = 0 */;
int c;
int ent;
int disp;
int hsize_reg;
int hshift;
// Set up the globals: g_init_bits - initial number of bits
g_init_bits = init_bits;
// Set up the necessary values
clear_flg = false;
n_bits = g_init_bits;
maxcode = MAXCODE(n_bits);
ClearCode = 1 << (init_bits - 1);
EOFCode = ClearCode + 1;
free_ent = ClearCode + 2;
char_init();
ent = GIFNextPixel();
hshift = 0;
for (fcode = hsize; fcode < 65536; fcode *= 2)
++hshift;
hshift = 8 - hshift; // set hash code range bound
hsize_reg = hsize;
cl_hash(hsize_reg); // clear hash table
output(ClearCode, outs);
outer_loop: while ((c = GIFNextPixel()) != EOF) {
fcode = (c << maxbits) + ent;
i = (c << hshift) ^ ent; // xor hashing
if (htab[i] == fcode) {
ent = codetab[i];
continue;
} else if (htab[i] >= 0) // non-empty slot
{
disp = hsize_reg - i; // secondary hash (after G. Knott)
if (i == 0)
disp = 1;
do {
if ((i -= disp) < 0)
i += hsize_reg;
if (htab[i] == fcode) {
ent = codetab[i];
continue outer_loop;
}
} while (htab[i] >= 0);
}
output(ent, outs);
ent = c;
if (free_ent < maxmaxcode) {
codetab[i] = free_ent++; // code -> hashtable
htab[i] = fcode;
} else
cl_block(outs);
}
// Put out the final code.
output(ent, outs);
output(EOFCode, outs);
}
// output
//
// Output the given code.
// Inputs:
// code: A n_bits-bit integer. If == -1, then EOF. This assumes
// that n_bits =< wordsize - 1.
// Outputs:
// Outputs code to the file.
// Assumptions:
// Chars are 8 bits long.
// Algorithm:
// Maintain a BITS character long buffer (so that 8 codes will
// fit in it exactly). Use the VAX insv instruction to insert each
// code in turn. When the buffer fills up empty it and start over.
int cur_accum = 0;
int cur_bits = 0;
int masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF,
0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };
void output(int code, OutputStream outs) throws IOException {
cur_accum &= masks[cur_bits];
if (cur_bits > 0)
cur_accum |= (code << cur_bits);
else
cur_accum = code;
cur_bits += n_bits;
while (cur_bits >= 8) {
char_out((byte) (cur_accum & 0xff), outs);
cur_accum >>= 8;
cur_bits -= 8;
}
// If the next entry is going to be too big for the code size,
// then increase it, if possible.
if (free_ent > maxcode || clear_flg) {
if (clear_flg) {
maxcode = MAXCODE(n_bits = g_init_bits);
clear_flg = false;
} else {
++n_bits;
if (n_bits == maxbits)
maxcode = maxmaxcode;
else
maxcode = MAXCODE(n_bits);
}
}
if (code == EOFCode) {
// At EOF, write the rest of the buffer.
while (cur_bits > 0) {
char_out((byte) (cur_accum & 0xff), outs);
cur_accum >>= 8;
cur_bits -= 8;
}
flush_char(outs);
}
}
// Clear out the hash table
// table clear for block compress
void cl_block(OutputStream outs) throws IOException {
cl_hash(hsize);
free_ent = ClearCode + 2;
clear_flg = true;
output(ClearCode, outs);
}
// reset code table
void cl_hash(int hsize) {
for (int i = 0; i < hsize; ++i)
htab[i] = -1;
}
// GIF Specific routines
// Number of characters so far in this 'packet'
int a_count;
// Set up the 'byte output' routine
void char_init() {
a_count = 0;
}
// Define the storage for the packet accumulator
byte[] accum = new byte[256];
// Add a character to the end of the current packet, and if it is 254
// characters, flush the packet to disk.
void char_out(byte c, OutputStream outs) throws IOException {
accum[a_count++] = c;
if (a_count >= 254)
flush_char(outs);
}
// Flush the packet to disk, and reset the accumulator
void flush_char(OutputStream outs) throws IOException {
if (a_count > 0) {
outs.write(a_count);
outs.write(accum, 0, a_count);
a_count = 0;
}
}
}
