/**
* Read and decompress a new scanline from the specified {@link Inflater}. If more data is needed,
* then {@code null} is returned.
*/
public ScanlineWrapper readNext(Inflater inflater) throws IOException {
try {
// Decompress the filter-type first, that is
// contained as first byte in a scanline
if (ftype == FILTER_INVALID) {
inflater.inflate(buffer, 0, 1);
ftype = buffer[0];
}
// Decompress one scanline, skipping the already read bytes
final int numBytesRequired = length - offset;
final int numBytesInflated = inflater.inflate(buffer, offset, numBytesRequired);
if (numBytesInflated != numBytesRequired) {
// A full scanline could not be read or decompressed, save
// the position inside the buffer and wait for more input
offset = numBytesInflated;
return null;
} else offset = 0;
} catch (DataFormatException dfe) {
// Rethrow as IOException
throw new IOException(dfe);
}
// Ensure a valid filter-type!
if (ftype < FILTER_NONE || ftype > FILTER_PAETH)
throw new IOException("Invalid filter type found: " + ftype);
// Reconstruct the decompressed scanline using its filter
final int[] curline = this.getCurScanline();
final int[] preline = this.getPreScanline();
final IScanlineFilter filter = LUT_FILTERS[ftype];
filter.reconstruct(curline, preline, buffer, length, delta);
// Prepare for next reconstruction
ftype = FILTER_INVALID;
// Swap the scanlines!
curid = 1 - curid;
++numScanlinesRead;
// Return the reconstructed scanline
wrapper.setScanline(curline, 0, width);
return wrapper;
}
