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	/*
	* Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.imageio.plugins.png;

	public class RowFilter {

	private static final int abs(int x) {
	return (x < 0) ? -x : x;
	}

	// Returns the sum of absolute differences
	protected static int subFilter(byte[] currRow,
	byte[] subFilteredRow,
	int bytesPerPixel,
	int bytesPerRow) {
	int badness = 0;
	for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
	int curr = currRow[i] & 0xff;
	int left = currRow[i - bytesPerPixel] & 0xff;
	int difference = curr - left;
	subFilteredRow[i] = (byte)difference;

	badness += abs(difference);
	}

	return badness;
	}

	// Returns the sum of absolute differences
	protected static int upFilter(byte[] currRow,
	byte[] prevRow,
	byte[] upFilteredRow,
	int bytesPerPixel,
	int bytesPerRow) {
	int badness = 0;
	for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
	int curr = currRow[i] & 0xff;
	int up = prevRow[i] & 0xff;
	int difference = curr - up;
	upFilteredRow[i] = (byte)difference;

	badness += abs(difference);
	}

	return badness;
	}

	protected final int paethPredictor(int a, int b, int c) {
	int p = a + b - c;
	int pa = abs(p - a);
	int pb = abs(p - b);
	int pc = abs(p - c);

	if ((pa <= pb) && (pa <= pc)) {
	return a;
	} else if (pb <= pc) {
	return b;
	} else {
	return c;
	}
	}

	public int filterRow(int colorType,
	byte[] currRow,
	byte[] prevRow,
	byte[][] scratchRows,
	int bytesPerRow,
	int bytesPerPixel) {

	// Use type 0 for palette images
	if (colorType != PNGImageReader.PNG_COLOR_PALETTE) {
	System.arraycopy(currRow, bytesPerPixel,
	scratchRows[0], bytesPerPixel,
	bytesPerRow);
	return 0;
	}

	int[] filterBadness = new int[5];
	for (int i = 0; i < 5; i++) {
	filterBadness[i] = Integer.MAX_VALUE;
	}

	{
	int badness = 0;

	for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
	int curr = currRow[i] & 0xff;
	badness += curr;
	}

	filterBadness[0] = badness;
	}

	{
	byte[] subFilteredRow = scratchRows[1];
	int badness = subFilter(currRow,
	subFilteredRow,
	bytesPerPixel,
	bytesPerRow);

	filterBadness[1] = badness;
	}

	{
	byte[] upFilteredRow = scratchRows[2];
	int badness = upFilter(currRow,
	prevRow,
	upFilteredRow,
	bytesPerPixel,
	bytesPerRow);

	filterBadness[2] = badness;
	}

	{
	byte[] averageFilteredRow = scratchRows[3];
	int badness = 0;

	for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
	int curr = currRow[i] & 0xff;
	int left = currRow[i - bytesPerPixel] & 0xff;
	int up = prevRow[i] & 0xff;
	int difference = curr - (left + up)/2;;
	averageFilteredRow[i] = (byte)difference;

	badness += abs(difference);
	}

	filterBadness[3] = badness;
	}

	{
	byte[] paethFilteredRow = scratchRows[4];
	int badness = 0;

	for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
	int curr = currRow[i] & 0xff;
	int left = currRow[i - bytesPerPixel] & 0xff;
	int up = prevRow[i] & 0xff;
	int upleft = prevRow[i - bytesPerPixel] & 0xff;
	int predictor = paethPredictor(left, up, upleft);
	int difference = curr - predictor;
	paethFilteredRow[i] = (byte)difference;

	badness += abs(difference);
	}

	filterBadness[4] = badness;
	}

	int minBadness = filterBadness[0];
	int filterType = 0;

	for (int i = 1; i < 5; i++) {
	if (filterBadness[i] < minBadness) {
	minBadness = filterBadness[i];
	filterType = i;
	}
	}

	if (filterType == 0) {
	System.arraycopy(currRow, bytesPerPixel,
	scratchRows[0], bytesPerPixel,
	bytesPerRow);
	}

	return filterType;
	}
	}

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