1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package android.support.car.ui; 17 18 import android.content.Context; 19 import android.graphics.Color; 20 import android.util.Log; 21 22 public class ColorChecker { 23 private static final String TAG = "GH.ColorChecker"; 24 private static final double MIN_CONTRAST_RATIO = 4.5; 25 /** 26 * Non-critical information doesn't have to meet as stringent contrast requirements. 27 */ 28 private static final double MIN_NON_CRITICAL_CONTRAST_RATIO = 1.5; 29 30 /** 31 * Calls {@link #getTintColor(int, int...)} with: 32 * {@link R.color#car_tint_light} and 33 * {@link R.color#car_tint_dark} 34 */ 35 public static int getTintColor(Context context, int backgroundColor) { 36 int lightTintColor = context.getResources().getColor(R.color.car_tint_light); 37 int darkTintColor = context.getResources().getColor(R.color.car_tint_dark); 38 39 return getTintColor(backgroundColor, lightTintColor, darkTintColor); 40 } 41 42 /** 43 * Calls {@link #getNonCriticalTintColor(int, int...)} with: 44 * {@link R.color#car_tint_light} and 45 * {@link R.color#car_tint_dark} 46 */ 47 public static int getNonCriticalTintColor(Context context, int backgroundColor) { 48 int lightTintColor = context.getResources().getColor(R.color.car_tint_light); 49 int darkTintColor = context.getResources().getColor(R.color.car_tint_dark); 50 51 return getNonCriticalTintColor(backgroundColor, lightTintColor, darkTintColor); 52 } 53 54 /** 55 * Calls {@link #getTintColor(int, int...)} with {@link #MIN_CONTRAST_RATIO}. 56 */ 57 public static int getTintColor(int backgroundColor, int... tintColors) { 58 return getTintColor(MIN_CONTRAST_RATIO, backgroundColor, tintColors); 59 } 60 61 /** 62 * Calls {@link #getTintColor(int, int...)} with {@link #MIN_NON_CRITICAL_CONTRAST_RATIO}. 63 */ 64 public static int getNonCriticalTintColor(int backgroundColor, int... tintColors) { 65 return getTintColor(MIN_NON_CRITICAL_CONTRAST_RATIO, backgroundColor, tintColors); 66 } 67 68 /** 69 * 70 * Determines what color to tint icons given the background color that they sit on. 71 * 72 * @param minAllowedContrastRatio The minimum contrast ratio 73 * @param bgColor The background color that the icons sit on. 74 * @param tintColors A list of potential colors to tint the icons with. 75 * @return The color that the icons should be tinted. Will be the first tinted color that 76 * meets the requirements. If none of the tint colors meet the minimum requirements, 77 * either black or white will be returned, whichever has a higher contrast. 78 */ 79 public static int getTintColor(double minAllowedContrastRatio, int bgColor, int... tintColors) { 80 for (int tc : tintColors) { 81 double contrastRatio = getContrastRatio(bgColor, tc); 82 if (contrastRatio >= minAllowedContrastRatio) { 83 return tc; 84 } 85 } 86 double blackContrastRatio = getContrastRatio(bgColor, Color.BLACK); 87 double whiteContrastRatio = getContrastRatio(bgColor, Color.WHITE); 88 if (whiteContrastRatio >= blackContrastRatio) { 89 Log.w(TAG, "Tint color does not meet contrast requirements. Using white."); 90 return Color.WHITE; 91 } else { 92 Log.w(TAG, "Tint color does not meet contrast requirements. Using black."); 93 return Color.BLACK; 94 } 95 } 96 97 public static double getContrastRatio(int color1, int color2) { 98 return getContrastRatio(getLuminance(color1), getLuminance(color2)); 99 } 100 101 public static double getContrastRatio(double luminance1, double luminance2) { 102 return (Math.max(luminance1, luminance2) + 0.05) / 103 (Math.min(luminance1, luminance2) + 0.05); 104 } 105 106 /** 107 * Calculates the luminance of a color as specified by: 108 * http://www.w3.org/TR/WCAG20-TECHS/G17.html 109 * 110 * @param color The color to calculate the luminance of. 111 * @return The luminance. 112 */ 113 public static double getLuminance(int color) { 114 // Values are in sRGB 115 double r = convert8BitToLuminanceComponent(Color.red(color)); 116 double g = convert8BitToLuminanceComponent(Color.green(color)); 117 double b = convert8BitToLuminanceComponent(Color.blue(color)); 118 return r * 0.2126 + g * 0.7152 + b * 0.0722; 119 } 120 121 /** 122 * Converts am 8 bit color component (0-255) to the luminance component as specified by: 123 * http://www.w3.org/TR/WCAG20-TECHS/G17.html 124 */ 125 private static double convert8BitToLuminanceComponent(double component) { 126 component /= 255.0; 127 if (component <= 0.03928) { 128 return component / 12.92; 129 } else { 130 return Math.pow(((component + 0.055) / 1.055), 2.4); 131 } 132 } 133 } 134
