/**
* 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;
}
/**
* Prepare this {@link ScanlineReader} for reading new scanlines of specified width and with
* specified number of samples-per-pixel and bits-per-sample.
*/
public void prepare(int width, int spp, int bps) {
final int n = bps >> 3;
// Update the current ScanlineWrapper:
// bps = 1,2,4 --> bps >> 3 = 0
// bps = 8 --> bps >> 3 = 1
// bps = 16 --> bps >> 3 = 2
wrapper = wrappers[n];
wrapper.prepare(bps);
// For reconstruction of a byte of the pixel X the corresponding
// byte in the pixel immediately before X should be used. But when
// the bitdepth is less than 8, then simply use the previous byte.
this.delta = (bps < 8) ? 1 : (spp * n);
this.width = width;
this.numScanlinesRead = 0;
this.ftype = FILTER_INVALID;
this.offset = 0;
// Calculate the sanline's length in bytes
final int numbits = spp * bps * width;
this.length = (numbits >> 3);
if ((numbits & 0x07) != 0) {
// numbits is not a multiple of 8,
// one additional byte is needed!
++length;
}
// Update the buffers for scanlines
if (buffer.length < length) {
buffer = new byte[length];
scanlines[0] = new int[length];
scanlines[1] = new int[length];
}
}