/*
* Copyright (c) 2005, 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
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*/
package com.sun.imageio.plugins.common;
import java.awt.Point;
import java.awt.Rectangle;
import java.io.IOException;
import javax.imageio.stream.ImageInputStream;
/**
* This class contains utility methods that may be useful to ImageReader
* plugins. Ideally these methods would be in the ImageReader base class
* so that all subclasses could benefit from them, but that would be an
* addition to the existing API, and it is not yet clear whether these methods
* are universally useful, so for now we will leave them here.
*/
public class ReaderUtil {
// Helper for computeUpdatedPixels method
private static void computeUpdatedPixels(int sourceOffset,
int sourceExtent,
int destinationOffset,
int dstMin,
int dstMax,
int sourceSubsampling,
int passStart,
int passExtent,
int passPeriod,
int[] vals,
int offset)
{
// We need to satisfy the congruences:
// dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
//
// src - passStart == 0 (mod passPeriod)
// src - sourceOffset == 0 (mod sourceSubsampling)
//
// subject to the inequalities:
//
// src >= passStart
// src < passStart + passExtent
// src >= sourceOffset
// src < sourceOffset + sourceExtent
// dst >= dstMin
// dst <= dstmax
//
// where
//
// dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
//
// For now we use a brute-force approach although we could
// attempt to analyze the congruences. If passPeriod and
// sourceSubsamling are relatively prime, the period will be
// their product. If they share a common factor, either the
// period will be equal to the larger value, or the sequences
// will be completely disjoint, depending on the relationship
// between passStart and sourceOffset. Since we only have to do this
// twice per image (once each for X and Y), it seems cheap enough
// to do it the straightforward way.
boolean gotPixel = false;
int firstDst = -1;
int secondDst = -1;
int lastDst = -1;
for (int i = 0; i < passExtent; i++) {
int src = passStart + i*passPeriod;
if (src < sourceOffset) {
continue;
}
if ((src - sourceOffset) % sourceSubsampling != 0) {
continue;
}
if (src >= sourceOffset + sourceExtent) {
break;
}
int dst = destinationOffset +
(src - sourceOffset)/sourceSubsampling;
if (dst < dstMin) {
continue;
}
if (dst > dstMax) {
break;
}
if (!gotPixel) {
firstDst = dst; // Record smallest valid pixel
gotPixel = true;
} else if (secondDst == -1) {
secondDst = dst; // Record second smallest valid pixel
}
lastDst = dst; // Record largest valid pixel
}
vals[offset] = firstDst;
// If we never saw a valid pixel, set width to 0
if (!gotPixel) {
vals[offset + 2] = 0;
} else {
vals[offset + 2] = lastDst - firstDst + 1;
}
// The period is given by the difference of any two adjacent pixels
vals[offset + 4] = Math.max(secondDst - firstDst, 1);
}
/**
* A utility method that computes the exact set of destination
* pixels that will be written during a particular decoding pass.
* The intent is to simplify the work done by readers in combining
* the source region, source subsampling, and destination offset
* information obtained from the <code>ImageReadParam</code> with
* the offsets and periods of a progressive or interlaced decoding
* pass.
*
* @param sourceRegion a <code>Rectangle</code> containing the
* source region being read, offset by the source subsampling
* offsets, and clipped against the source bounds, as returned by
* the <code>getSourceRegion</code> method.
* @param destinationOffset a <code>Point</code> containing the
* coordinates of the upper-left pixel to be written in the
* destination.
* @param dstMinX the smallest X coordinate (inclusive) of the
* destination <code>Raster</code>.
* @param dstMinY the smallest Y coordinate (inclusive) of the
* destination <code>Raster</code>.
* @param dstMaxX the largest X coordinate (inclusive) of the destination
* <code>Raster</code>.
* @param dstMaxY the largest Y coordinate (inclusive) of the destination
* <code>Raster</code>.
* @param sourceXSubsampling the X subsampling factor.
* @param sourceYSubsampling the Y subsampling factor.
* @param passXStart the smallest source X coordinate (inclusive)
* of the current progressive pass.
* @param passYStart the smallest source Y coordinate (inclusive)
* of the current progressive pass.
* @param passWidth the width in pixels of the current progressive
* pass.
* @param passHeight the height in pixels of the current progressive
* pass.
* @param passPeriodX the X period (horizontal spacing between
* pixels) of the current progressive pass.
* @param passPeriodY the Y period (vertical spacing between
* pixels) of the current progressive pass.
*
* @return an array of 6 <code>int</code>s containing the
* destination min X, min Y, width, height, X period and Y period
* of the region that will be updated.
*/
public static int[] computeUpdatedPixels(Rectangle sourceRegion,
Point destinationOffset,
int dstMinX,
int dstMinY,
int dstMaxX,
int dstMaxY,
int sourceXSubsampling,
int sourceYSubsampling,
int passXStart,
int passYStart,
int passWidth,
int passHeight,
int passPeriodX,
int passPeriodY)
{
int[] vals = new int[6];
computeUpdatedPixels(sourceRegion.x, sourceRegion.width,
destinationOffset.x,
dstMinX, dstMaxX, sourceXSubsampling,
passXStart, passWidth, passPeriodX,
vals, 0);
computeUpdatedPixels(sourceRegion.y, sourceRegion.height,
destinationOffset.y,
dstMinY, dstMaxY, sourceYSubsampling,
passYStart, passHeight, passPeriodY,
vals, 1);
return vals;
}
public static int readMultiByteInteger(ImageInputStream iis)
throws IOException
{
int value = iis.readByte();
int result = value & 0x7f;
while((value & 0x80) == 0x80) {
result <<= 7;
value = iis.readByte();
result |= (value & 0x7f);
}
return result;
}
}