Java tutorial
/* * Copyright 2015 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.support.v4.graphics; import android.graphics.Color; import android.support.annotation.ColorInt; import android.support.annotation.FloatRange; import android.support.annotation.IntRange; import android.support.annotation.NonNull; import android.support.annotation.VisibleForTesting; /** * A set of color-related utility methods, building upon those available in {@code Color}. */ public final class ColorUtils { private static final double XYZ_WHITE_REFERENCE_X = 95.047; private static final double XYZ_WHITE_REFERENCE_Y = 100; private static final double XYZ_WHITE_REFERENCE_Z = 108.883; private static final double XYZ_EPSILON = 0.008856; private static final double XYZ_KAPPA = 903.3; private static final int MIN_ALPHA_SEARCH_MAX_ITERATIONS = 10; private static final int MIN_ALPHA_SEARCH_PRECISION = 1; private static final ThreadLocal<double[]> TEMP_ARRAY = new ThreadLocal<>(); private ColorUtils() { } /** * Composite two potentially translucent colors over each other and returns the result. */ public static int compositeColors(@ColorInt int foreground, @ColorInt int background) { int bgAlpha = Color.alpha(background); int fgAlpha = Color.alpha(foreground); int a = compositeAlpha(fgAlpha, bgAlpha); int r = compositeComponent(Color.red(foreground), fgAlpha, Color.red(background), bgAlpha, a); int g = compositeComponent(Color.green(foreground), fgAlpha, Color.green(background), bgAlpha, a); int b = compositeComponent(Color.blue(foreground), fgAlpha, Color.blue(background), bgAlpha, a); return Color.argb(a, r, g, b); } private static int compositeAlpha(int foregroundAlpha, int backgroundAlpha) { return 0xFF - (((0xFF - backgroundAlpha) * (0xFF - foregroundAlpha)) / 0xFF); } private static int compositeComponent(int fgC, int fgA, int bgC, int bgA, int a) { if (a == 0) return 0; return ((0xFF * fgC * fgA) + (bgC * bgA * (0xFF - fgA))) / (a * 0xFF); } /** * Returns the luminance of a color as a float between {@code 0.0} and {@code 1.0}. * <p>Defined as the Y component in the XYZ representation of {@code color}.</p> */ @FloatRange(from = 0.0, to = 1.0) public static double calculateLuminance(@ColorInt int color) { final double[] result = getTempDouble3Array(); colorToXYZ(color, result); // Luminance is the Y component return result[1] / 100; } /** * Returns the contrast ratio between {@code foreground} and {@code background}. * {@code background} must be opaque. * <p> * Formula defined * <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef">here</a>. */ public static double calculateContrast(@ColorInt int foreground, @ColorInt int background) { if (Color.alpha(background) != 255) { throw new IllegalArgumentException( "background can not be translucent: #" + Integer.toHexString(background)); } if (Color.alpha(foreground) < 255) { // If the foreground is translucent, composite the foreground over the background foreground = compositeColors(foreground, background); } final double luminance1 = calculateLuminance(foreground) + 0.05; final double luminance2 = calculateLuminance(background) + 0.05; // Now return the lighter luminance divided by the darker luminance return Math.max(luminance1, luminance2) / Math.min(luminance1, luminance2); } /** * Calculates the minimum alpha value which can be applied to {@code foreground} so that would * have a contrast value of at least {@code minContrastRatio} when compared to * {@code background}. * * @param foreground the foreground color * @param background the opaque background color * @param minContrastRatio the minimum contrast ratio * @return the alpha value in the range 0-255, or -1 if no value could be calculated */ public static int calculateMinimumAlpha(@ColorInt int foreground, @ColorInt int background, float minContrastRatio) { if (Color.alpha(background) != 255) { throw new IllegalArgumentException( "background can not be translucent: #" + Integer.toHexString(background)); } // First lets check that a fully opaque foreground has sufficient contrast int testForeground = setAlphaComponent(foreground, 255); double testRatio = calculateContrast(testForeground, background); if (testRatio < minContrastRatio) { // Fully opaque foreground does not have sufficient contrast, return error return -1; } // Binary search to find a value with the minimum value which provides sufficient contrast int numIterations = 0; int minAlpha = 0; int maxAlpha = 255; while (numIterations <= MIN_ALPHA_SEARCH_MAX_ITERATIONS && (maxAlpha - minAlpha) > MIN_ALPHA_SEARCH_PRECISION) { final int testAlpha = (minAlpha + maxAlpha) / 2; testForeground = setAlphaComponent(foreground, testAlpha); testRatio = calculateContrast(testForeground, background); if (testRatio < minContrastRatio) { minAlpha = testAlpha; } else { maxAlpha = testAlpha; } numIterations++; } // Conservatively return the max of the range of possible alphas, which is known to pass. return maxAlpha; } /** * Convert RGB components to HSL (hue-saturation-lightness). * <ul> * <li>outHsl[0] is Hue [0 .. 360)</li> * <li>outHsl[1] is Saturation [0...1]</li> * <li>outHsl[2] is Lightness [0...1]</li> * </ul> * * @param r red component value [0..255] * @param g green component value [0..255] * @param b blue component value [0..255] * @param outHsl 3-element array which holds the resulting HSL components */ public static void RGBToHSL(@IntRange(from = 0x0, to = 0xFF) int r, @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b, @NonNull float[] outHsl) { final float rf = r / 255f; final float gf = g / 255f; final float bf = b / 255f; final float max = Math.max(rf, Math.max(gf, bf)); final float min = Math.min(rf, Math.min(gf, bf)); final float deltaMaxMin = max - min; float h, s; float l = (max + min) / 2f; if (max == min) { // Monochromatic h = s = 0f; } else { if (max == rf) { h = ((gf - bf) / deltaMaxMin) % 6f; } else if (max == gf) { h = ((bf - rf) / deltaMaxMin) + 2f; } else { h = ((rf - gf) / deltaMaxMin) + 4f; } s = deltaMaxMin / (1f - Math.abs(2f * l - 1f)); } h = (h * 60f) % 360f; if (h < 0) { h += 360f; } outHsl[0] = constrain(h, 0f, 360f); outHsl[1] = constrain(s, 0f, 1f); outHsl[2] = constrain(l, 0f, 1f); } /** * Convert the ARGB color to its HSL (hue-saturation-lightness) components. * <ul> * <li>outHsl[0] is Hue [0 .. 360)</li> * <li>outHsl[1] is Saturation [0...1]</li> * <li>outHsl[2] is Lightness [0...1]</li> * </ul> * * @param color the ARGB color to convert. The alpha component is ignored * @param outHsl 3-element array which holds the resulting HSL components */ public static void colorToHSL(@ColorInt int color, @NonNull float[] outHsl) { RGBToHSL(Color.red(color), Color.green(color), Color.blue(color), outHsl); } /** * Convert HSL (hue-saturation-lightness) components to a RGB color. * <ul> * <li>hsl[0] is Hue [0 .. 360)</li> * <li>hsl[1] is Saturation [0...1]</li> * <li>hsl[2] is Lightness [0...1]</li> * </ul> * If hsv values are out of range, they are pinned. * * @param hsl 3-element array which holds the input HSL components * @return the resulting RGB color */ @ColorInt public static int HSLToColor(@NonNull float[] hsl) { final float h = hsl[0]; final float s = hsl[1]; final float l = hsl[2]; final float c = (1f - Math.abs(2 * l - 1f)) * s; final float m = l - 0.5f * c; final float x = c * (1f - Math.abs((h / 60f % 2f) - 1f)); final int hueSegment = (int) h / 60; int r = 0, g = 0, b = 0; switch (hueSegment) { case 0: r = Math.round(255 * (c + m)); g = Math.round(255 * (x + m)); b = Math.round(255 * m); break; case 1: r = Math.round(255 * (x + m)); g = Math.round(255 * (c + m)); b = Math.round(255 * m); break; case 2: r = Math.round(255 * m); g = Math.round(255 * (c + m)); b = Math.round(255 * (x + m)); break; case 3: r = Math.round(255 * m); g = Math.round(255 * (x + m)); b = Math.round(255 * (c + m)); break; case 4: r = Math.round(255 * (x + m)); g = Math.round(255 * m); b = Math.round(255 * (c + m)); break; case 5: case 6: r = Math.round(255 * (c + m)); g = Math.round(255 * m); b = Math.round(255 * (x + m)); break; } r = constrain(r, 0, 255); g = constrain(g, 0, 255); b = constrain(b, 0, 255); return Color.rgb(r, g, b); } /** * Set the alpha component of {@code color} to be {@code alpha}. */ @ColorInt public static int setAlphaComponent(@ColorInt int color, @IntRange(from = 0x0, to = 0xFF) int alpha) { if (alpha < 0 || alpha > 255) { throw new IllegalArgumentException("alpha must be between 0 and 255."); } return (color & 0x00ffffff) | (alpha << 24); } /** * Convert the ARGB color to its CIE Lab representative components. * * @param color the ARGB color to convert. The alpha component is ignored * @param outLab 3-element array which holds the resulting LAB components */ public static void colorToLAB(@ColorInt int color, @NonNull double[] outLab) { RGBToLAB(Color.red(color), Color.green(color), Color.blue(color), outLab); } /** * Convert RGB components to its CIE Lab representative components. * * <ul> * <li>outLab[0] is L [0 ...1)</li> * <li>outLab[1] is a [-128...127)</li> * <li>outLab[2] is b [-128...127)</li> * </ul> * * @param r red component value [0..255] * @param g green component value [0..255] * @param b blue component value [0..255] * @param outLab 3-element array which holds the resulting LAB components */ public static void RGBToLAB(@IntRange(from = 0x0, to = 0xFF) int r, @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b, @NonNull double[] outLab) { // First we convert RGB to XYZ RGBToXYZ(r, g, b, outLab); // outLab now contains XYZ XYZToLAB(outLab[0], outLab[1], outLab[2], outLab); // outLab now contains LAB representation } /** * Convert the ARGB color to it's CIE XYZ representative components. * * <p>The resulting XYZ representation will use the D65 illuminant and the CIE * 2 Standard Observer (1931).</p> * * <ul> * <li>outXyz[0] is X [0 ...95.047)</li> * <li>outXyz[1] is Y [0...100)</li> * <li>outXyz[2] is Z [0...108.883)</li> * </ul> * * @param color the ARGB color to convert. The alpha component is ignored * @param outXyz 3-element array which holds the resulting LAB components */ public static void colorToXYZ(@ColorInt int color, @NonNull double[] outXyz) { RGBToXYZ(Color.red(color), Color.green(color), Color.blue(color), outXyz); } /** * Convert RGB components to it's CIE XYZ representative components. * * <p>The resulting XYZ representation will use the D65 illuminant and the CIE * 2 Standard Observer (1931).</p> * * <ul> * <li>outXyz[0] is X [0 ...95.047)</li> * <li>outXyz[1] is Y [0...100)</li> * <li>outXyz[2] is Z [0...108.883)</li> * </ul> * * @param r red component value [0..255] * @param g green component value [0..255] * @param b blue component value [0..255] * @param outXyz 3-element array which holds the resulting XYZ components */ public static void RGBToXYZ(@IntRange(from = 0x0, to = 0xFF) int r, @IntRange(from = 0x0, to = 0xFF) int g, @IntRange(from = 0x0, to = 0xFF) int b, @NonNull double[] outXyz) { if (outXyz.length != 3) { throw new IllegalArgumentException("outXyz must have a length of 3."); } double sr = r / 255.0; sr = sr < 0.04045 ? sr / 12.92 : Math.pow((sr + 0.055) / 1.055, 2.4); double sg = g / 255.0; sg = sg < 0.04045 ? sg / 12.92 : Math.pow((sg + 0.055) / 1.055, 2.4); double sb = b / 255.0; sb = sb < 0.04045 ? sb / 12.92 : Math.pow((sb + 0.055) / 1.055, 2.4); outXyz[0] = 100 * (sr * 0.4124 + sg * 0.3576 + sb * 0.1805); outXyz[1] = 100 * (sr * 0.2126 + sg * 0.7152 + sb * 0.0722); outXyz[2] = 100 * (sr * 0.0193 + sg * 0.1192 + sb * 0.9505); } /** * Converts a color from CIE XYZ to CIE Lab representation. * * <p>This method expects the XYZ representation to use the D65 illuminant and the CIE * 2 Standard Observer (1931).</p> * * <ul> * <li>outLab[0] is L [0 ...1)</li> * <li>outLab[1] is a [-128...127)</li> * <li>outLab[2] is b [-128...127)</li> * </ul> * * @param x X component value [0...95.047) * @param y Y component value [0...100) * @param z Z component value [0...108.883) * @param outLab 3-element array which holds the resulting Lab components */ public static void XYZToLAB(@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_X) double x, @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Y) double y, @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Z) double z, @NonNull double[] outLab) { if (outLab.length != 3) { throw new IllegalArgumentException("outLab must have a length of 3."); } x = pivotXyzComponent(x / XYZ_WHITE_REFERENCE_X); y = pivotXyzComponent(y / XYZ_WHITE_REFERENCE_Y); z = pivotXyzComponent(z / XYZ_WHITE_REFERENCE_Z); outLab[0] = Math.max(0, 116 * y - 16); outLab[1] = 500 * (x - y); outLab[2] = 200 * (y - z); } /** * Converts a color from CIE Lab to CIE XYZ representation. * * <p>The resulting XYZ representation will use the D65 illuminant and the CIE * 2 Standard Observer (1931).</p> * * <ul> * <li>outXyz[0] is X [0 ...95.047)</li> * <li>outXyz[1] is Y [0...100)</li> * <li>outXyz[2] is Z [0...108.883)</li> * </ul> * * @param l L component value [0...100) * @param a A component value [-128...127) * @param b B component value [-128...127) * @param outXyz 3-element array which holds the resulting XYZ components */ public static void LABToXYZ(@FloatRange(from = 0f, to = 100) final double l, @FloatRange(from = -128, to = 127) final double a, @FloatRange(from = -128, to = 127) final double b, @NonNull double[] outXyz) { final double fy = (l + 16) / 116; final double fx = a / 500 + fy; final double fz = fy - b / 200; double tmp = Math.pow(fx, 3); final double xr = tmp > XYZ_EPSILON ? tmp : (116 * fx - 16) / XYZ_KAPPA; final double yr = l > XYZ_KAPPA * XYZ_EPSILON ? Math.pow(fy, 3) : l / XYZ_KAPPA; tmp = Math.pow(fz, 3); final double zr = tmp > XYZ_EPSILON ? tmp : (116 * fz - 16) / XYZ_KAPPA; outXyz[0] = xr * XYZ_WHITE_REFERENCE_X; outXyz[1] = yr * XYZ_WHITE_REFERENCE_Y; outXyz[2] = zr * XYZ_WHITE_REFERENCE_Z; } /** * Converts a color from CIE XYZ to its RGB representation. * * <p>This method expects the XYZ representation to use the D65 illuminant and the CIE * 2 Standard Observer (1931).</p> * * @param x X component value [0...95.047) * @param y Y component value [0...100) * @param z Z component value [0...108.883) * @return int containing the RGB representation */ @ColorInt public static int XYZToColor(@FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_X) double x, @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Y) double y, @FloatRange(from = 0f, to = XYZ_WHITE_REFERENCE_Z) double z) { double r = (x * 3.2406 + y * -1.5372 + z * -0.4986) / 100; double g = (x * -0.9689 + y * 1.8758 + z * 0.0415) / 100; double b = (x * 0.0557 + y * -0.2040 + z * 1.0570) / 100; r = r > 0.0031308 ? 1.055 * Math.pow(r, 1 / 2.4) - 0.055 : 12.92 * r; g = g > 0.0031308 ? 1.055 * Math.pow(g, 1 / 2.4) - 0.055 : 12.92 * g; b = b > 0.0031308 ? 1.055 * Math.pow(b, 1 / 2.4) - 0.055 : 12.92 * b; return Color.rgb(constrain((int) Math.round(r * 255), 0, 255), constrain((int) Math.round(g * 255), 0, 255), constrain((int) Math.round(b * 255), 0, 255)); } /** * Converts a color from CIE Lab to its RGB representation. * * @param l L component value [0...100] * @param a A component value [-128...127] * @param b B component value [-128...127] * @return int containing the RGB representation */ @ColorInt public static int LABToColor(@FloatRange(from = 0f, to = 100) final double l, @FloatRange(from = -128, to = 127) final double a, @FloatRange(from = -128, to = 127) final double b) { final double[] result = getTempDouble3Array(); LABToXYZ(l, a, b, result); return XYZToColor(result[0], result[1], result[2]); } /** * Returns the euclidean distance between two LAB colors. */ public static double distanceEuclidean(@NonNull double[] labX, @NonNull double[] labY) { return Math.sqrt( Math.pow(labX[0] - labY[0], 2) + Math.pow(labX[1] - labY[1], 2) + Math.pow(labX[2] - labY[2], 2)); } private static float constrain(float amount, float low, float high) { return amount < low ? low : (amount > high ? high : amount); } private static int constrain(int amount, int low, int high) { return amount < low ? low : (amount > high ? high : amount); } private static double pivotXyzComponent(double component) { return component > XYZ_EPSILON ? Math.pow(component, 1 / 3.0) : (XYZ_KAPPA * component + 16) / 116; } /** * Blend between two ARGB colors using the given ratio. * * <p>A blend ratio of 0.0 will result in {@code color1}, 0.5 will give an even blend, * 1.0 will result in {@code color2}.</p> * * @param color1 the first ARGB color * @param color2 the second ARGB color * @param ratio the blend ratio of {@code color1} to {@code color2} */ @ColorInt public static int blendARGB(@ColorInt int color1, @ColorInt int color2, @FloatRange(from = 0.0, to = 1.0) float ratio) { final float inverseRatio = 1 - ratio; float a = Color.alpha(color1) * inverseRatio + Color.alpha(color2) * ratio; float r = Color.red(color1) * inverseRatio + Color.red(color2) * ratio; float g = Color.green(color1) * inverseRatio + Color.green(color2) * ratio; float b = Color.blue(color1) * inverseRatio + Color.blue(color2) * ratio; return Color.argb((int) a, (int) r, (int) g, (int) b); } /** * Blend between {@code hsl1} and {@code hsl2} using the given ratio. This will interpolate * the hue using the shortest angle. * * <p>A blend ratio of 0.0 will result in {@code hsl1}, 0.5 will give an even blend, * 1.0 will result in {@code hsl2}.</p> * * @param hsl1 3-element array which holds the first HSL color * @param hsl2 3-element array which holds the second HSL color * @param ratio the blend ratio of {@code hsl1} to {@code hsl2} * @param outResult 3-element array which holds the resulting HSL components */ public static void blendHSL(@NonNull float[] hsl1, @NonNull float[] hsl2, @FloatRange(from = 0.0, to = 1.0) float ratio, @NonNull float[] outResult) { if (outResult.length != 3) { throw new IllegalArgumentException("result must have a length of 3."); } final float inverseRatio = 1 - ratio; // Since hue is circular we will need to interpolate carefully outResult[0] = circularInterpolate(hsl1[0], hsl2[0], ratio); outResult[1] = hsl1[1] * inverseRatio + hsl2[1] * ratio; outResult[2] = hsl1[2] * inverseRatio + hsl2[2] * ratio; } /** * Blend between two CIE-LAB colors using the given ratio. * * <p>A blend ratio of 0.0 will result in {@code lab1}, 0.5 will give an even blend, * 1.0 will result in {@code lab2}.</p> * * @param lab1 3-element array which holds the first LAB color * @param lab2 3-element array which holds the second LAB color * @param ratio the blend ratio of {@code lab1} to {@code lab2} * @param outResult 3-element array which holds the resulting LAB components */ public static void blendLAB(@NonNull double[] lab1, @NonNull double[] lab2, @FloatRange(from = 0.0, to = 1.0) double ratio, @NonNull double[] outResult) { if (outResult.length != 3) { throw new IllegalArgumentException("outResult must have a length of 3."); } final double inverseRatio = 1 - ratio; outResult[0] = lab1[0] * inverseRatio + lab2[0] * ratio; outResult[1] = lab1[1] * inverseRatio + lab2[1] * ratio; outResult[2] = lab1[2] * inverseRatio + lab2[2] * ratio; } @VisibleForTesting static float circularInterpolate(float a, float b, float f) { if (Math.abs(b - a) > 180) { if (b > a) { a += 360; } else { b += 360; } } return (a + ((b - a) * f)) % 360; } private static double[] getTempDouble3Array() { double[] result = TEMP_ARRAY.get(); if (result == null) { result = new double[3]; TEMP_ARRAY.set(result); } return result; } }