sketcher2/src/com/jotuntech/sketcher/common/PixelUnpacker.java

package com.jotuntech.sketcher.common;

import java.util.zip.DataFormatException;
import java.util.zip.Inflater;


public class PixelUnpacker {
	Inflater inflater;
	private byte[] encodedPixels;

	public PixelUnpacker() {
		inflater = new Inflater(true);
	}

	public void unpack(byte[] input, int ofs, int len, int[] output) {
		if(encodedPixels == null || encodedPixels.length < input.length * 6) {
			encodedPixels = new byte[output.length * 6];
		}

		inflater.reset();
		inflater.setInput(input, ofs, len);
		//Log.debug("Inflating from offset " + ofs + " length " + len);

		int encodedLength = 0;
		try {
			while(!inflater.finished() && encodedLength < encodedPixels.length) {
				encodedLength += inflater.inflate(encodedPixels, encodedLength, encodedPixels.length - encodedLength);
			}
		} catch(DataFormatException e) {
			throw new RuntimeException(e);
		}

		if(encodedLength < output.length * 6) {
			Log.error("needsInput = " + inflater.needsInput());
			throw new RuntimeException("Encoded length " + encodedLength + " is shorter than output length " + output.length * 6 + ".");
		}

		int lastAlpha = 0, lastY = 0, lastCb = 256, lastCr = 256;
		for(int outputOffset = 0, YOffset = output.length, CbOffset = output.length * 2, CrOffset = output.length * 4; outputOffset < output.length; outputOffset++, YOffset++, CbOffset++, CrOffset++) {
			/* Extract alpha channel delta */
			int deltaAlpha = encodedPixels[outputOffset] & 0xFF;

			/* Differential transform with overflow wrapping */
			int alpha = (lastAlpha + deltaAlpha) & 0xFF;
			lastAlpha = alpha;

			/* Color channel deltas are always zero when alpha is zero */
			if(alpha == 0) {
				output[outputOffset] = 0;
				++CbOffset;
				++CrOffset;
			} else {
				/* Extract color channel deltas */
				int deltaY = encodedPixels[YOffset] & 0xFF;
				int deltaCb = ((encodedPixels[CbOffset++] & 0xFF) << 8) | (encodedPixels[CbOffset] & 0xFF);
				int deltaCr = ((encodedPixels[CrOffset++] & 0xFF) << 8) | (encodedPixels[CrOffset] & 0xFF);

				/* Differental transform with overflow wrapping */
				int Y = (lastY + deltaY) & 0xFF;
				int Cb = (lastCb + deltaCb) & 0x1FF;
				int Cr = (lastCr + deltaCr) & 0x1FF;
				lastY = Y;
				lastCb = Cb;
				lastCr = Cr;

				/* Inverse color transform */
				Cb -= 256;
				Cr -= 256;
				int green = Y - ((Cb + Cr) >> 2);
				int red = Cr + green;
				int blue = Cb + green;

				output[outputOffset] = Pixels.pack(alpha, red, green, blue);
			}
		}
	}
}