| /* |
| * 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; |
| |
| /** |
| * A set of color-related utility methods, building upon those available in {@code Color}. |
| */ |
| public class ColorUtils { |
| |
| private static final int MIN_ALPHA_SEARCH_MAX_ITERATIONS = 10; |
| private static final int MIN_ALPHA_SEARCH_PRECISION = 1; |
| |
| 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. |
| * <p> |
| * Formula defined |
| * <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef">here</a>. |
| * </p> |
| */ |
| @FloatRange(from = 0.0, to = 1.0) |
| public static double calculateLuminance(@ColorInt int color) { |
| double red = Color.red(color) / 255d; |
| red = red < 0.03928 ? red / 12.92 : Math.pow((red + 0.055) / 1.055, 2.4); |
| |
| double green = Color.green(color) / 255d; |
| green = green < 0.03928 ? green / 12.92 : Math.pow((green + 0.055) / 1.055, 2.4); |
| |
| double blue = Color.blue(color) / 255d; |
| blue = blue < 0.03928 ? blue / 12.92 : Math.pow((blue + 0.055) / 1.055, 2.4); |
| |
| return (0.2126 * red) + (0.7152 * green) + (0.0722 * blue); |
| } |
| |
| /** |
| * 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 background color. Should be opaque. |
| * @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>hsl[0] is Hue [0 .. 360)</li> |
| * <li>hsl[1] is Saturation [0...1]</li> |
| * <li>hsl[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 hsl 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[] hsl) { |
| 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; |
| } |
| |
| hsl[0] = constrain(h, 0f, 360f); |
| hsl[1] = constrain(s, 0f, 1f); |
| hsl[2] = constrain(l, 0f, 1f); |
| } |
| |
| /** |
| * Convert the ARGB color to its HSL (hue-saturation-lightness) components. |
| * <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> |
| * |
| * @param color the ARGB color to convert. The alpha component is ignored. |
| * @param hsl 3 element array which holds the resulting HSL components. |
| */ |
| public static void colorToHSL(@ColorInt int color, @NonNull float[] hsl) { |
| RGBToHSL(Color.red(color), Color.green(color), Color.blue(color), hsl); |
| } |
| |
| /** |
| * 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); |
| } |
| |
| 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); |
| } |
| |
| } |
