J2ME GIF Decoder Animation


import java.io.*;
import java.util.*;
import javax.microedition.lcdui.*;

/**
* Class GifDecoder - Decodes a GIF file into one or more frames.
*
* Example:
* GifDecoder d = new GifDecoder();
* d.read("sample.gif");
* int n = d.getFrameCount();
* for (int i = 0; i < n; i++) { * BufferedImage frame = d.getFrame(i); // frame i * int t = d.getDelay(i); // display duration of frame in milliseconds * // do something with frame * } * * No copyright asserted on the source code of this class. May be used for * any purpose, however, refer to the Unisys LZW patent for any additional * restrictions. I am not responsible if your phone blows up. : ) * * @author: Jitsu Wan with reference to work done by Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's ImageMagick. * @version 1.03 November 2004 * */ public class Helix_GifDecoder { /** * File read status: No errors. */ public static final int STATUS_OK = 0; /** * File read status: Error decoding file (may be partially decoded) */ public static final int STATUS_FORMAT_ERROR = 1; /** * File read status: Unable to open source. */ public static final int STATUS_OPEN_ERROR = 2; protected byte[] in; protected int status; protected int width; // full image width protected int height; // full image height protected boolean gctFlag; // global color table used protected int gctSize; // size of global color table protected int loopCount = 1; // iterations; 0 = repeat forever protected int[] gct; // global color table protected int[] lct; // local color table protected int[] act; // active color table protected int bgIndex; // background color index protected int bgColor; // background color protected int lastBgColor; // previous bg color protected int pixelAspect; // pixel aspect ratio protected boolean lctFlag; // local color table flag protected boolean interlace; // interlace flag protected int lctSize; // local color table size protected int ix, iy, iw, ih; // current image rectangle protected int[] lastRect; // last image rect protected Image image; // current frame protected Image lastImage; // previous frame protected byte[] block = new byte[256]; // current data block protected int blockSize = 0; // block size // last graphic control extension info protected int dispose = 0; // 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev protected int lastDispose = 0; protected boolean transparency = false; // use transparent color protected int delay = 0; // delay in milliseconds protected int transIndex; // transparent color index protected static final int MaxStackSize = 4096; // max decoder pixel stack size // LZW decoder working arrays protected short[] prefix; protected byte[] suffix; protected byte[] pixelStack; protected byte[] pixels; protected Vector frames; // frames read from current file protected int frameCount; static class GifFrame { public GifFrame(Image im, int del) { image = im; delay = del; } public Image image; public int delay; } /** * Gets display duration for specified frame. * * @param n int index of frame * @return delay in milliseconds */ public int getDelay(int n) { // delay = -1; if ((n >= 0) && (n < frameCount)) { delay = ((GifFrame) frames.elementAt(n)).delay; } return delay; } /** * Gets the number of frames read from file. * @return frame count */ public int getFrameCount() { return frameCount; } /** * Gets the first (or only) image read. * * @return BufferedImage containing first frame, or null if none. */ public Image getImage() { return getFrame(0); } /** * Gets the "Netscape" iteration count, if any. * A count of 0 means repeat indefinitiely. * * @return iteration count if one was specified, else 1. */ public int getLoopCount() { return loopCount; } /** * Creates new frame image from current data (and previous * frames as specified by their disposition codes). */ protected void setPixels() { // expose destination image's pixels as int array int[] dest =new int[image.getWidth()*image.getHeight()]; image.getRGB(dest, 0,0,0,0,image.getWidth(), image.getHeight()); // fill in starting image contents based on last image's dispose code if (lastDispose > 0) {
if (lastDispose == 3) {
// use image before last
int n = frameCount - 2;
if (n > 0) {
lastImage = getFrame(n - 1);
} else {
lastImage = null;
}
}

if (lastImage != null) {
int[] prev = new int[lastImage.getHeight()*lastImage.getWidth()];
lastImage.getRGB(prev, 0,0,0,0,lastImage.getWidth(), lastImage.getHeight());
System.arraycopy(prev, 0, dest, 0, width * height);
// copy pixels

if (lastDispose == 2) {
// fill last image rect area with background color
Graphics g = image.getGraphics();

if (transparency) {
g.setColor(0x00000000); // assume background is transparent
} else {
g.setColor(lastBgColor); // use given background color
}

g.fillRect(lastRect[0],lastRect[1],lastRect[2],lastRect[3]);

}
}
}

// copy each source line to the appropriate place in the destination
int pass = 1;
int inc = 8;
int iline = 0;
for (int i = 0; i < ih; i++) { int line = i; if (interlace) { if (iline >= ih) {
pass++;
switch (pass) {
case 2 :
iline = 4;
break;
case 3 :
iline = 2;
inc = 4;
break;
case 4 :
iline = 1;
inc = 2;
}
}
line = iline;
iline += inc;
}
line += iy;
if (line < height) { int k = line * width; int dx = k + ix; // start of line in dest int dlim = dx + iw; // end of dest line if ((k + width) < dlim) { dlim = k + width; // past dest edge } int sx = i * iw; // start of line in source while (dx < dlim) { // map color and insert in destination int index = ((int) pixels[sx++]) & 0xff; int c = act[index]; if (c != 0) { dest[dx] = c; } dx++; } } } } /** * Gets the image contents of frame n. * * @return BufferedImage representation of frame, or null if n is invalid. */ public Image getFrame(int n) { Image im = null; if ((n >= 0) && (n < frameCount)) { im = ((GifFrame) frames.elementAt(n)).image; } return im; } /** * Gets image size. * * @return GIF image dimensions */ public int[] getFrameSize() { int[] dimension = new int[2]; dimension[0] = width; dimension[1] = height; return dimension; } /** * * This method loads the GifDecoder with a GIF image byte array * * This is a modification from the original GifDecoder, which accepts a InputStream and is geared towards direct loading from the connection. * The Helix_Parser takes care of this in this case and therefore no streaming is required. * * CHANGES: * * Remove any DataInputStream functionality * Replace with byte[] reading functionality. * * Strip away unwanted methods. * Better understand LZW compression * * Consider legal issues. * * **/ public int read(byte[] raw) { init(); if (raw != null) { in = raw; readHeader(); if (!err()) { readContents(); if (frameCount < 0) { status = STATUS_FORMAT_ERROR; } } } else { status = STATUS_OPEN_ERROR; } return status; } /** * Decodes LZW image data into pixel array. * Adapted from John Cristy's ImageMagick. */ protected void decodeImageData() { int NullCode = -1; int npix = iw * ih; int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first, top, bi, pi; if ((pixels == null) || (pixels.length < npix)) { pixels = new byte[npix]; // allocate new pixel array } if (prefix == null) prefix = new short[MaxStackSize]; if (suffix == null) suffix = new byte[MaxStackSize]; if (pixelStack == null) pixelStack = new byte[MaxStackSize + 1]; // Initialize GIF data stream decoder. data_size = read(); clear = 1 << data_size; end_of_information = clear + 1; available = clear + 2; old_code = NullCode; code_size = data_size + 1; code_mask = (1 << code_size) - 1; for (code = 0; code < clear; code++) { prefix[code] = 0; suffix[code] = (byte) code; } // Decode GIF pixel stream. datum = bits = count = first = top = pi = bi = 0; for (i = 0; i < npix;) { if (top == 0) { if (bits < code_size) { // Load bytes until there are enough bits for a code. if (count == 0) { // Read a new data block. count = readBlock(); if (count <= 0) break; bi = 0; } datum += (((int) block[bi]) & 0xff) << bits; bits += 8; bi++; count--; continue; } // Get the next code. code = datum & code_mask; datum >>= code_size;
bits -= code_size;

// Interpret the code

if ((code > available) || (code == end_of_information))
break;
if (code == clear) {
// Reset decoder.
code_size = data_size + 1;
code_mask = (1 << code_size) - 1; available = clear + 2; old_code = NullCode; continue; } if (old_code == NullCode) { pixelStack[top++] = suffix[code]; old_code = code; first = code; continue; } in_code = code; if (code == available) { pixelStack[top++] = (byte) first; code = old_code; } while (code > clear) {
pixelStack[top++] = suffix[code];
code = prefix[code];
}
first = ((int) suffix[code]) & 0xff;

// Add a new string to the string table,

if (available >= MaxStackSize)
break;
pixelStack[top++] = (byte) first;
prefix[available] = (short) old_code;
suffix[available] = (byte) first;
available++;
if (((available & code_mask) == 0)
&& (available < MaxStackSize)) { code_size++; code_mask += available; } old_code = in_code; } // Pop a pixel off the pixel stack. top--; pixels[pi++] = pixelStack[top]; i++; } for (i = pi; i < npix; i++) { pixels[i] = 0; // clear missing pixels } } /** * Returns true if an error was encountered during reading/decoding */ protected boolean err() { return status != STATUS_OK; } /** * Initializes or re-initializes reader */ protected void init() { status = STATUS_OK; frameCount = 0; frames = new Vector(); gct = null; lct = null; } protected int readCounter = 0; /** * Reads a single byte from the input stream. */ protected int read() { int curByte = 0; try { curByte = in[readCounter]; readCounter++; } catch (IOException e) { status = STATUS_FORMAT_ERROR; } return curByte; } /** * Reads next variable length block from input. * * @return number of bytes stored in "buffer" */ protected int readBlock() { blockSize = read(); int n = 0; if (blockSize > 0) {
try {
int count = 0;
while (n < blockSize) { count = in.read(block, n, blockSize - n); if (count == -1) break; n += count; } } catch (IOException e) { } if (n < blockSize) { status = STATUS_FORMAT_ERROR; } } return n; } /** * Reads color table as 256 RGB integer values * * @param ncolors int number of colors to read * @return int array containing 256 colors (packed ARGB with full alpha) */ protected int[] readColorTable(int ncolors) { int nbytes = 3 * ncolors; int[] tab = null; byte[] c = new byte[nbytes]; int n = 0; try { n = in.read(c); } catch (IOException e) { } if (n < nbytes) { status = STATUS_FORMAT_ERROR; } else { tab = new int[256]; // max size to avoid bounds checks int i = 0; int j = 0; while (i < ncolors) { int r = ((int) c[j++]) & 0xff; int g = ((int) c[j++]) & 0xff; int b = ((int) c[j++]) & 0xff; tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b; } } return tab; } /** * Main file parser. Reads GIF content blocks. */ protected void readContents() { // read GIF file content blocks boolean done = false; while (!(done || err())) { int code = read(); switch (code) { case 0x2C : // image separator readImage(); break; case 0x21 : // extension code = read(); switch (code) { case 0xf9 : // graphics control extension readGraphicControlExt(); break; case 0xff : // application extension readBlock(); String app = ""; for (int i = 0; i < 11; i++) { app += (char) block[i]; } if (app.equals("NETSCAPE2.0")) { readNetscapeExt(); } else skip(); // don't care break; default : // uninteresting extension skip(); } break; case 0x3b : // terminator done = true; break; case 0x00 : // bad byte, but keep going and see what happens break; default : status = STATUS_FORMAT_ERROR; } } } /** * Reads Graphics Control Extension values */ protected void readGraphicControlExt() { read(); // block size int packed = read(); // packed fields dispose = (packed & 0x1c) >> 2; // disposal method
if (dispose == 0) {
dispose = 1; // elect to keep old image if discretionary
}
transparency = (packed & 1) != 0;
delay = readShort() * 10; // delay in milliseconds
transIndex = read(); // transparent color index
read(); // block terminator
}

/**
* Reads GIF file header information.
*/
protected void readHeader() {
String id = "";
for (int i = 0; i < 6; i++) { id += (char) read(); } if (!id.startsWith("GIF")) { status = STATUS_FORMAT_ERROR; return; } readLSD(); if (gctFlag && !err()) { gct = readColorTable(gctSize); bgColor = gct[bgIndex]; } } /** * Reads next frame image */ protected void readImage() { ix = readShort(); // (sub)image position & size iy = readShort(); iw = readShort(); ih = readShort(); int packed = read(); lctFlag = (packed & 0x80) != 0; // 1 - local color table flag interlace = (packed & 0x40) != 0; // 2 - interlace flag // 3 - sort flag // 4-5 - reserved lctSize = 2 << (packed & 7); // 6-8 - local color table size if (lctFlag) { lct = readColorTable(lctSize); // read table act = lct; // make local table active } else { act = gct; // make global table active if (bgIndex == transIndex) bgColor = 0; } int save = 0; if (transparency) { save = act[transIndex]; act[transIndex] = 0; // set transparent color if specified } if (act == null) { status = STATUS_FORMAT_ERROR; // no color table defined } if (err()) return; decodeImageData(); // decode pixel data skip(); if (err()) return; frameCount++; // create new image to receive frame data image.createImage(width, height); setPixels(); // transfer pixel data to image frames.addElement(new GifFrame(image, delay)); // add image to frame list if (transparency) { act[transIndex] = save; } resetFrame(); } /** * Reads Logical Screen Descriptor */ protected void readLSD() { // logical screen size width = readShort(); height = readShort(); // packed fields int packed = read(); gctFlag = (packed & 0x80) != 0; // 1 : global color table flag // 2-4 : color resolution // 5 : gct sort flag gctSize = 2 << (packed & 7); // 6-8 : gct size bgIndex = read(); // background color index pixelAspect = read(); // pixel aspect ratio } /** * Reads Netscape extenstion to obtain iteration count */ protected void readNetscapeExt() { do { readBlock(); if (block[0] == 1) { // loop count sub-block int b1 = ((int) block[1]) & 0xff; int b2 = ((int) block[2]) & 0xff; loopCount = (b2 << 8) | b1; } } while ((blockSize > 0) && !err());
}

/**
* Reads next 16-bit value, LSB first
*/
protected int readShort() {
// read 16-bit value, LSB first
return read() | (read() << 8); } /** * Resets frame state for reading next image. */ protected void resetFrame() { lastDispose = dispose; lastRect = new int[4]; lastRect[0] = ix; lastRect[1] = iy; lastRect[2] = iw; lastRect[3] = ih; lastImage = image; lastBgColor = bgColor; int dispose = 0; boolean transparency = false; int delay = 0; lct = null; } /** * Skips variable length blocks up to and including * next zero length block. */ protected void skip() { do { readBlock(); } while ((blockSize > 0) && !err());
}
}