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

package com.jotuntech.sketcher.common;

import java.util.zip.Deflater;

public class PixelPacker {
	private Deflater deflater;
	private byte[] encodedPixels = null;

	public PixelPacker() {
		deflater = new Deflater(Deflater.BEST_COMPRESSION, true);
	}

	public int pack(int[] pixels, byte[] output) {
		return pack(pixels, output, 0, output.length);
	}

	public int pack(int[] pixels, byte[] output, int ofs, int len) {
		/* Create buffers, or enlarge them if they are too small */
		if(encodedPixels == null || encodedPixels.length < pixels.length * 6) {
			encodedPixels = new byte[pixels.length * 6];
		}

		int lastAlpha = 0, lastY = 0, lastCb = 256, lastCr = 256;
		for(int pixelOffset = 0, YOffset = pixels.length, CbOffset = pixels.length * 2, CrOffset = pixels.length * 4; pixelOffset < pixels.length; pixelOffset++, YOffset++, CbOffset++, CrOffset++) {
			int pixel = pixels[pixelOffset];

			/* Extract alpha channel */
			int alpha = (pixel >> 24) & 0xFF;

			/* Differential transform */
			int deltaAlpha = alpha - lastAlpha;
			lastAlpha = alpha;

			/* Convert negative deltas to equivalent positive deltas */
			if(deltaAlpha < 0) {
				deltaAlpha = 256 + deltaAlpha;
			}

			/* Luma and chroma deltas */
			int deltaY, deltaCb, deltaCr;

			/* Color deltas are zero if alpha is zero, for better compression */
			if(alpha == 0) {
				deltaY = 0;
				deltaCb = 0;
				deltaCr = 0;
			} else {
				/* Extract color channels */
				int red = (pixel >> 16) & 0xFF;
				int green = (pixel >> 8) & 0xFF;
				int blue = pixel & 0xFF;

				/* Forward color transform  */
				int Y = (red + (green << 1) + blue) >> 2;
				int Cb = 256 + blue - green;
				int Cr = 256 + red - green;

				/* Differential transform */
				deltaY = Y - lastY;
				deltaCb = Cb - lastCb;
				deltaCr = Cr - lastCr;
				lastY = Y;
				lastCb = Cb;
				lastCr = Cr;

				/* Convert negative deltas to equivalent positive deltas */
				if(deltaY < 0) {
					deltaY = 256 + deltaY;
				}

				if(deltaCb < 0) {
					deltaCb = 512 + deltaCb;
				}

				if(deltaCr < 0) {
					deltaCr = 512 + deltaCr;
				}
			}

			/* Store image channels */
			encodedPixels[pixelOffset] = (byte) deltaAlpha;
			encodedPixels[YOffset] = (byte) deltaY;
			encodedPixels[CbOffset++] = (byte) (deltaCb >>> 8);
			encodedPixels[CbOffset] = (byte) deltaCb;
			encodedPixels[CrOffset++] = (byte) (deltaCr >>> 8);
			encodedPixels[CrOffset] = (byte) deltaCr;
		}

		/* Deflate encoded pixels */
		deflater.reset();
		deflater.setInput(encodedPixels, 0, pixels.length * 6);
		deflater.finish();
		int compressedLength = 0;
		while(!deflater.finished() && compressedLength < len) {
			compressedLength += deflater.deflate(output, ofs + compressedLength, len - compressedLength);
		}
		return compressedLength;
	}
}