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* Copyright (c) 2009-2021 jMonkeyEngine
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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package com.jme3.terrain.heightmap;
import com.jme3.math.FastMath;
import java.util.Random;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* MidpointDisplacementHeightMap generates a heightmap based on
* the midpoint displacement algorithm. See Constructor javadoc for more info.
* @author cghislai
*/
public class MidpointDisplacementHeightMap extends AbstractHeightMap {
private static final Logger logger = Logger.getLogger(MidpointDisplacementHeightMap.class.getName());
private float range; // The offset in which randomness will be added
private float persistence; // How the random offset evolves with increasing passes
private long seed; // seed for random number generator
/**
* The constructor generates the heightmap. After the first 4 corners are
* randomly given a height, the center height will be set to the average of
* the 4 corners plus a random value. Then other passes fill
* the heightmap by the same principle.
* The random value is generated between the values -range
* and range. The range parameter is multiplied by
* the persistence parameter each pass to smoothen close cell heights.
* Extends this class and override the getOffset function for more control of
* the randomness (you can use the coordinates and/or the computed average height
* to influence the random amount added.
*
* @param size
* The size of the heightmap, must be 2^N+1
* @param range
* The range in which randomness will be added. A value of 1 will
* allow -1 to 1 value changes.
* @param persistence
* The factor by which the range will evolve at each iteration.
* A value of 0.5f will halve the range at each iteration and is
* typically a good choice
* @param seed
* A seed to feed the random number generator.
* @throws IllegalArgumentException if size is not a power of two plus one.
*/
public MidpointDisplacementHeightMap(int size, float range, float persistence, long seed) {
if (size < 0 || !FastMath.isPowerOfTwo(size - 1)) {
throw new IllegalArgumentException("The size is negative or not of the form 2^N +1"
+ " (a power of two plus one)");
}
this.size = size;
this.range = range;
this.persistence = persistence;
this.seed = seed;
load();
}
/**
* The constructor generates the heightmap. After the first 4 corners are
* randomly given a height, the center height will be set to the average of
* the 4 corners plus a random value. Then other passes fill
* the heightmap by the same principle.
* The random value is generated between the values -range
* and range. The range parameter is multiplied by
* the persistence parameter each pass to smoothen close cell heights.
* @param size
* The size of the heightmap, must be 2^N+1
* @param range
* The range in which randomness will be added. A value of 1 will
* allow -1 to 1 value changes.
* @param persistence
* The factor by which the range will evolve at each iteration.
* A value of 0.5f will halve the range at each iteration and is
* typically a good choice
* @throws IllegalArgumentException if size is not a power of two plus one.
*/
public MidpointDisplacementHeightMap(int size, float range, float persistence) throws Exception {
this(size, range, persistence, new Random().nextLong());
}
/**
* Generate the heightmap.
* @return true
*/
@Override
public boolean load() {
// clean up data if needed.
if (null != heightData) {
unloadHeightMap();
}
heightData = new float[size * size];
float[][] tempBuffer = new float[size][size];
Random random = new Random(seed);
tempBuffer[0][0] = random.nextFloat();
tempBuffer[0][size - 1] = random.nextFloat();
tempBuffer[size - 1][0] = random.nextFloat();
tempBuffer[size - 1][size - 1] = random.nextFloat();
float offsetRange = range;
int stepSize = size - 1;
while (stepSize > 1) {
int[] nextCoords = {0, 0};
while (nextCoords != null) {
nextCoords = doSquareStep(tempBuffer, nextCoords, stepSize, offsetRange, random);
}
nextCoords = new int[]{0, 0};
while (nextCoords != null) {
nextCoords = doDiamondStep(tempBuffer, nextCoords, stepSize, offsetRange, random);
}
stepSize /= 2;
offsetRange *= persistence;
}
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
setHeightAtPoint(tempBuffer[i][j], j, i);
}
}
normalizeTerrain(NORMALIZE_RANGE);
logger.log(Level.FINE, "Midpoint displacement heightmap generated");
return true;
}
/**
* Will fill the value at (coords[0]+stepSize/2, coords[1]+stepSize/2) with
* the average from the corners of the square with top, left corner at (coords[0],coords[1])
* and width of stepSize.
* @param tempBuffer the temporary heightmap
* @param coords an int array of length 2 with the x coord in position 0
* @param stepSize the size of the square
* @param offsetRange the offset range within a random value is picked and added to the average
* @param random the random generator
* @return a new array or null
*/
protected int[] doSquareStep(float[][] tempBuffer, int[] coords, int stepSize, float offsetRange, Random random) {
float cornerAverage = 0;
int x = coords[0];
int y = coords[1];
cornerAverage += tempBuffer[x][y];
cornerAverage += tempBuffer[x + stepSize][y];
cornerAverage += tempBuffer[x + stepSize][y + stepSize];
cornerAverage += tempBuffer[x][y + stepSize];
cornerAverage /= 4;
float offset = getOffset(random, offsetRange, coords, cornerAverage);
tempBuffer[x + stepSize / 2][y + stepSize / 2] = cornerAverage + offset;
// Only get to next square if the center is still in map
if (x + stepSize * 3 / 2 < size) {
return new int[]{x + stepSize, y};
}
if (y + stepSize * 3 / 2 < size) {
return new int[]{0, y + stepSize};
}
return null;
}
/**
* Will fill the cell at (x+stepSize/2, y) with the average of the 4 corners
* of the diamond centered on that point with width and height of stepSize.
* @param tempBuffer
* @param coords
* @param stepSize
* @param offsetRange
* @param random
* @return a new array or null
*/
protected int[] doDiamondStep(float[][] tempBuffer, int[] coords, int stepSize, float offsetRange, Random random) {
int cornerNbr = 0;
float cornerAverage = 0;
int x = coords[0];
int y = coords[1];
int[] dxs = new int[]{0, stepSize / 2, stepSize, stepSize / 2};
int[] dys = new int[]{0, -stepSize / 2, 0, stepSize / 2};
for (int d = 0; d < 4; d++) {
int i = x + dxs[d];
if (i < 0 || i > size - 1) {
continue;
}
int j = y + dys[d];
if (j < 0 || j > size - 1) {
continue;
}
cornerAverage += tempBuffer[i][j];
cornerNbr++;
}
cornerAverage /= cornerNbr;
float offset = getOffset(random, offsetRange, coords, cornerAverage);
tempBuffer[x + stepSize / 2][y] = cornerAverage + offset;
if (x + stepSize * 3 / 2 < size) {
return new int[]{x + stepSize, y};
}
if (y + stepSize / 2 < size) {
if (x + stepSize == size - 1) {
return new int[]{-stepSize / 2, y + stepSize / 2};
} else {
return new int[]{0, y + stepSize / 2};
}
}
return null;
}
/**
* Generate a random value to add to the computed average
* @param random the random generator
* @param offsetRange
* @param coords
* @param average
* @return A semi-random value within offsetRange
*/
protected float getOffset(Random random, float offsetRange, int[] coords, float average) {
return 2 * (random.nextFloat() - 0.5F) * offsetRange;
}
public float getPersistence() {
return persistence;
}
public void setPersistence(float persistence) {
this.persistence = persistence;
}
public float getRange() {
return range;
}
public void setRange(float range) {
this.range = range;
}
public long getSeed() {
return seed;
}
public void setSeed(long seed) {
this.seed = seed;
}
}
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