org.apache.sanselan.formats.icns.Rle24Compression Maven / Gradle / Ivy

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.sanselan.formats.icns;

class Rle24Compression
{
	public static byte[] decompress(int width, int height, byte[] data)
	{
		final int pixelCount = width * height;
		final byte[] result = new byte[4 * pixelCount];

		// Several ICNS parsers advance by 4 bytes here:
		// http://code.google.com/p/icns2png/ - when the width is >= 128
		// http://icns.sourceforge.net/ - when those 4 bytes are all zero
		//
		// A scan of all .icns files on MacOS shows that
		// all 128x128 images indeed start with 4 zeroes,
		// while all smaller images don't.
		// However it is dangerous to assume
		// that 4 initial zeroes always need to be skipped,
		// because they could encode valid pixels on smaller images.
		// So always skip on 128x128, and never skip on anything else.
		int dataPos = 0;
		if (width >= 128 && height >= 128)
			dataPos = 4;

		// argb, band by band in 3 passes, with no alpha
		for (int band = 1; band <= 3; band++)
		{
			int remaining = pixelCount;
			int resultPos = 0;
			while (remaining > 0)
			{
				if ((data[dataPos] & 0x80) != 0)
				{
					int count = (0xff & data[dataPos]) - 125;
					for (int i = 0; i < count; i++)
						result[band + 4*(resultPos++)] = data[dataPos + 1];
					dataPos += 2;
					remaining -= count;
				}
				else
				{
					int count = (0xff & data[dataPos]) + 1;
					dataPos++;
					for (int i = 0; i < count; i++)
						result[band + 4*(resultPos++)] = data[dataPos++];
					remaining -= count;
				}
			}
		}
		return result;
	}
}