/*******************************************************************************
* Copyright (c) 2006, 2008 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.jface.internal.text.revisions;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.RGB;
import org.eclipse.core.runtime.Assert;
/**
* Utility for color operations.
*
* @since 3.3
*/
public final class Colors {
/*
* Implementation note: Color computation assumes sRGB, which is probably not true, and does not
* always give good results. CIE based algorithms would be better, see
* http://www.w3.org/TR/PNG-ColorAppendix.html and http://en.wikipedia.org/wiki/Lab_color_space
*/
/**
* Returns the human-perceived brightness of a color as float in [0.0, 1.0]. The used RGB
* weights come from http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9.
*
* @param rgb the color
* @return the gray-scale value
*/
public static float brightness(RGB rgb) {
return Math.min(1f, (0.2126f * rgb.red + 0.7152f * rgb.green + 0.0722f * rgb.blue + 0.5f) / 255f);
}
/**
* Normalizes a color in its perceived brightness. Yellows are darkened, while blues and reds
* are lightened. Depending on the hue, the brightness range within the RGB gamut may be
* different, outside values are clipped. Note that this is an approximation; the returned RGB
* is not guaranteed to have the requested {@link #brightness(RGB) brightness}.
*
* @param color the color to normalize
* @param brightness the requested brightness, in [0, 1]
* @return a normalized version of <code>color</code>
* @see #brightness(RGB)
*/
public static RGB adjustBrightness(RGB color, float brightness) {
float[] hsi= toHSI(color);
float psychoFactor= brightness - brightness(color);
float weight= 0.5f; // found by trial and error
hsi[2]= Math.max(0, Math.min(1.0f, hsi[2] + psychoFactor * weight));
color= fromHSI(hsi);
return color;
}
/**
* Converts an {@link RGB} to an <a href="http://en.wikipedia.org/wiki/HSL_color_space">HSI</a>
* triplet.
*
* @param color the color to convert
* @return the HSI float array of length 3
*/
private static float[] toHSI(RGB color) {
float r = color.red / 255f;
float g = color.green / 255f;
float b = color.blue / 255f;
float max = Math.max(Math.max(r, g), b);
float min = Math.min(Math.min(r, g), b);
float delta = max - min;
float maxPlusMin= max + min;
float intensity = maxPlusMin / 2;
float saturation= intensity < 0.5 ? delta / maxPlusMin : delta / (2 - maxPlusMin);
float hue = 0;
if (delta != 0) {
if (r == max) {
hue = (g - b) / delta;
} else {
if (g == max) {
hue = 2 + (b - r) / delta;
} else {
hue = 4 + (r - g) / delta;
}
}
hue *= 60;
if (hue < 0) hue += 360;
}
return new float[] {hue, saturation, intensity};
}
/**
* Converts a <a href="http://en.wikipedia.org/wiki/HSL_color_space">HSI</a> triplet to an RGB.
*
* @param hsi the HSI values
* @return the RGB corresponding to the HSI spec
*/
private static RGB fromHSI(float[] hsi) {
float r, g, b;
float hue= hsi[0];
float saturation= hsi[1];
float intensity= hsi[2];
if (saturation == 0) {
r = g = b = intensity;
} else {
float temp2= intensity < 0.5f ? intensity * (1.0f + saturation) : (intensity + saturation) - (intensity * saturation);
float temp1= 2f * intensity - temp2;
if (hue == 360) hue = 0;
hue /= 360;
r= hue2RGB(temp1, temp2, hue + 1f/3f);
g= hue2RGB(temp1, temp2, hue);
b= hue2RGB(temp1, temp2, hue - 1f/3f);
}
int red = (int)(r * 255 + 0.5);
int green = (int)(g * 255 + 0.5);
int blue = (int)(b * 255 + 0.5);
return new RGB(red, green, blue);
}
private static float hue2RGB(float t1, float t2, float hue) {
if (hue < 0)
hue += 1;
else if (hue > 1)
hue -= 1;
if (6f * hue < 1)
return t1 +(t2 - t1) * 6f * hue;
if (2f * hue < 1)
return t2;
if (3f * hue < 2)
return t1 + (t2 - t1) * (2f/3f - hue) * 6f;
return t1;
}
/**
* Returns an RGB that lies between the given foreground and background
* colors using the given mixing factor. A <code>factor</code> of 1.0 will produce a
* color equal to <code>fg</code>, while a <code>factor</code> of 0.0 will produce one
* equal to <code>bg</code>.
* @param bg the background color
* @param fg the foreground color
* @param factor the mixing factor, must be in [0, 1]
*
* @return the interpolated color
*/
public static RGB blend(RGB bg, RGB fg, float factor) {
Assert.isLegal(bg != null);
Assert.isLegal(fg != null);
Assert.isLegal(factor >= 0f && factor <= 1f);
float complement= 1f - factor;
return new RGB(
(int) (complement * bg.red + factor * fg.red),
(int) (complement * bg.green + factor * fg.green),
(int) (complement * bg.blue + factor * fg.blue)
);
}
/**
* Returns an array of colors in a smooth palette from <code>start</code> to <code>end</code>.
* <p>
* The returned array has size <code>steps</code>, and the color at index 0 is <code>start</code>, the color
* at index <code>steps - 1</code> is <code>end</code>.
*
* @param start the start color of the palette
* @param end the end color of the palette
* @param steps the requested size, must be > 0
* @return an array of <code>steps</code> colors in the palette from <code>start</code> to <code>end</code>
*/
public static RGB[] palette(RGB start, RGB end, int steps) {
Assert.isLegal(start != null);
Assert.isLegal(end != null);
Assert.isLegal(steps > 0);
if (steps == 1)
return new RGB[] { start };
float step= 1.0f / (steps - 1);
RGB[] gradient= new RGB[steps];
for (int i= 0; i < steps; i++)
gradient[i]= blend(start, end, step * i);
return gradient;
}
/**
* Returns an array of colors with hues evenly distributed on the hue wheel defined by the <a
* href="http://en.wikipedia.org/wiki/HSV_color_space">HSB color space</a>. The returned array
* has size <code>steps</code>. The distance <var>d</var> between two successive colors is
* in [120°, 180°].
* <p>
* The color at a given <code>index</code> has the hue returned by
* {@linkplain #computeHue(int) computeHue(index)}; i.e. the computed hues are not equidistant,
* but adaptively distributed on the color wheel.
* </p>
* <p>
* The first six colors returned correspond to the following {@link SWT} color constants:
* {@link SWT#COLOR_RED red}, {@link SWT#COLOR_GREEN green}, {@link SWT#COLOR_BLUE blue},
* {@link SWT#COLOR_YELLOW yellow}, {@link SWT#COLOR_CYAN cyan},
* {@link SWT#COLOR_MAGENTA magenta}.
* </p>
*
* @param steps the requested size, must be >= 2
* @return an array of <code>steps</code> colors evenly distributed on the color wheel
*/
public static RGB[] rainbow(int steps) {
Assert.isLegal(steps >= 2);
RGB[] rainbow= new RGB[steps];
for (int i= 0; i < steps; i++)
rainbow[i]= new RGB(computeHue(i), 1f, 1f);
return rainbow;
}
/**
* Returns an indexed hue in [0°, 360°), distributing the hues evenly on the hue wheel
* defined by the <a href="http://en.wikipedia.org/wiki/HSV_color_space">HSB (or HSV) color
* space</a>. The distance <var>d</var> between two successive colors is in [120°, 180°].
* <p>
* The first six colors returned correspond to the following {@link SWT} color constants:
* {@link SWT#COLOR_RED red}, {@link SWT#COLOR_GREEN green}, {@link SWT#COLOR_BLUE blue},
* {@link SWT#COLOR_YELLOW yellow}, {@link SWT#COLOR_CYAN cyan},
* {@link SWT#COLOR_MAGENTA magenta}.
* </p>
*
* @param index the index of the color, must be >= 0
* @return a color hue in [0°, 360°)
* @see RGB#RGB(float, float, float)
*/
public static float computeHue(final int index) {
Assert.isLegal(index >= 0);
/*
* Base 3 gives a nice partitioning for RGB colors with red, green, blue being the colors
* 0,1,2, and yellow, cyan, magenta colors 3,4,5.
*/
final int base= 3;
final float range= 360f;
// partition the baseRange by using the least significant bit to select one half of the
// partitioning
int baseIndex= index / base;
float baseRange= range / base;
float baseOffset= 0f;
while (baseIndex > 0) {
baseRange /= 2;
int lsb= baseIndex % 2;
baseOffset += lsb * baseRange;
baseIndex >>= 1;
}
final int baseMod= index % base;
final float hue= baseOffset + baseMod * range / base;
Assert.isTrue(hue >= 0 && hue < 360);
return hue;
}
private Colors() {
// not instantiatable
}
}