/**
* Class GifDecoder - Decodes a GIF file into one or more frames. <br>
*
* <pre>
* 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
* }
* </pre>
*
* 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. Please forward any corrections to [email protected].
*
* @author Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's
* ImageMagick.
* @version 1.03 November 2003
*
*/
public class 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 BufferedInputStream 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 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 ArrayList frames; // frames read from current file
protected int frameCount;
static class GifFrame { public GifFrame(BufferedImage im, int del) {
image = im;
delay = del;
}
public BufferedImage 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.get(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 BufferedImage 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 = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();
// 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 (lastDispose == 2) {
// fill last image rect area with background color
Graphics2D g = image.createGraphics();
Color c = null; if (transparency) {
c = new Color(0, 0, 0, 0); // assume background is transparent
} else {
c = new Color(lastBgColor); // use given background color
}
g.setColor(c);
g.setComposite(AlphaComposite.Src); // replace area
g.fill(lastRect);
g.dispose();
}
}
}
// 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 BufferedImage getFrame(int n) {
BufferedImage im = null; if ((n >= 0) && (n < frameCount)) {
im = ((GifFrame) frames.get(n)).image;
} return im;
}
/**
* Reads GIF image from stream
*
* @param BufferedInputStream
* containing GIF file.
* @return read status code (0 = no errors)
*/ public int read(BufferedInputStream is) {
init(); if (is != null) {
in = is;
readHeader(); if (!err()) {
readContents(); if (frameCount < 0) {
status = STATUS_FORMAT_ERROR;
}
}
} else {
status = STATUS_OPEN_ERROR;
} try {
is.close();
} catch (IOException e) {
} return status;
}
/**
* Reads GIF image from stream
*
* @param InputStream
* containing GIF file.
* @return read status code (0 = no errors)
*/ public int read(InputStream is) {
init(); if (is != null) { if (!(is instanceof BufferedInputStream))
is = new BufferedInputStream(is);
in = (BufferedInputStream) is;
readHeader(); if (!err()) {
readContents(); if (frameCount < 0) {
status = STATUS_FORMAT_ERROR;
}
}
} else {
status = STATUS_OPEN_ERROR;
} try {
is.close();
} catch (IOException e) {
} return status;
}
/**
* Reads GIF file from specified file/URL source (URL assumed if name contains
* ":/" or "file:")
*
* @param name
* String containing source
* @return read status code (0 = no errors)
*/ public int read(String name) {
status = STATUS_OK; try {
name = name.trim().toLowerCase(); if ((name.indexOf("file:") >= 0) || (name.indexOf(":/") > 0)) {
URL url = new URL(name);
in = new BufferedInputStream(url.openStream());
} else {
in = new BufferedInputStream(new FileInputStream(name));
}
status = read(in);
} catch (IOException e) {
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];
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;
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 ArrayList();
gct = null;
lct = null;
}
/**
* Reads a single byte from the input stream.
*/ protected int read() { int curByte = 0; try {
curByte = in.read();
} 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;
}
/**
* 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 = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB_PRE);
setPixels(); // transfer pixel data to image
frames.add(new GifFrame(image, delay)); // add image to frame list
if (transparency) {
act[transIndex] = save;
}
resetFrame();
// 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 Rectangle(ix, iy, iw, 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());
}
}
