Colors.java
/**
* Copyright (c) 2017, RTE (http://www.rte-france.com)
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
* SPDX-License-Identifier: MPL-2.0
*/
package com.powsybl.commons.util;
import java.util.Objects;
import java.util.Random;
/**
* @author Geoffroy Jamgotchian {@literal <geoffroy.jamgotchian at rte-france.com>}
*/
public final class Colors {
private static final double GOLDEN_RATIO_CONJUGATE = 0.618033988749895;
private Colors() {
}
public static String[] generateColorScale(int n, Random random) {
if (n < 0) {
throw new IllegalArgumentException("Color scale size must be positive");
}
Objects.requireNonNull(random);
String[] colors = new String[n];
for (int i = 0; i < n; i++) {
double h = random.nextDouble();
h += GOLDEN_RATIO_CONJUGATE;
h %= 1;
long[] rgb = hsvToRgb(h, 0.5, 0.95);
String hex = String.format("#%02x%02x%02x", rgb[0], rgb[1], rgb[2]).toUpperCase();
colors[i] = hex;
}
return colors;
}
private static long[] hsvToRgb(double h, double s, double v) {
int hi = (int) Math.floor(h * 6);
double f = h * 6 - hi;
double p = v * (1 - s);
double q = v * (1 - f * s);
double t = v * (1 - (1 - f) * s);
double r;
double g;
double b;
switch (hi) {
case 0:
r = v;
g = t;
b = p;
break;
case 1:
r = q;
g = v;
b = p;
break;
case 2:
r = p;
g = v;
b = t;
break;
case 3:
r = p;
g = q;
b = v;
break;
case 4:
r = t;
g = p;
b = v;
break;
case 5:
r = v;
g = p;
b = q;
break;
default:
throw new IllegalStateException();
}
return new long[] {Math.round(r * 256), Math.round(g * 256), Math.round(b * 256)};
}
}