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 /** 23 * @hide 24 */ 25 public class ColorChecker { 26 private static final String TAG = "GH.ColorChecker"; 27 private static final double MIN_CONTRAST_RATIO = 4.5; 28 /** 29 * Non-critical information doesn't have to meet as stringent contrast requirements. 30 */ 31 private static final double MIN_NON_CRITICAL_CONTRAST_RATIO = 1.5; 32 33 /** 34 * Calls {@link #getTintColor(int, int...)} with: 35 * {@link R.color#car_tint_light} and 36 * {@link R.color#car_tint_dark} 37 */ getTintColor(Context context, int backgroundColor)38 public static int getTintColor(Context context, int backgroundColor) { 39 int lightTintColor = context.getResources().getColor(R.color.car_tint_light); 40 int darkTintColor = context.getResources().getColor(R.color.car_tint_dark); 41 42 return getTintColor(backgroundColor, lightTintColor, darkTintColor); 43 } 44 45 /** 46 * Calls {@link #getNonCriticalTintColor(int, int...)} with: 47 * {@link R.color#car_tint_light} and 48 * {@link R.color#car_tint_dark} 49 */ getNonCriticalTintColor(Context context, int backgroundColor)50 public static int getNonCriticalTintColor(Context context, int backgroundColor) { 51 int lightTintColor = context.getResources().getColor(R.color.car_tint_light); 52 int darkTintColor = context.getResources().getColor(R.color.car_tint_dark); 53 54 return getNonCriticalTintColor(backgroundColor, lightTintColor, darkTintColor); 55 } 56 57 /** 58 * Calls {@link #getTintColor(int, int...)} with {@link #MIN_CONTRAST_RATIO}. 59 */ getTintColor(int backgroundColor, int... tintColors)60 public static int getTintColor(int backgroundColor, int... tintColors) { 61 return getTintColor(MIN_CONTRAST_RATIO, backgroundColor, tintColors); 62 } 63 64 /** 65 * Calls {@link #getTintColor(int, int...)} with {@link #MIN_NON_CRITICAL_CONTRAST_RATIO}. 66 */ getNonCriticalTintColor(int backgroundColor, int... tintColors)67 public static int getNonCriticalTintColor(int backgroundColor, int... tintColors) { 68 return getTintColor(MIN_NON_CRITICAL_CONTRAST_RATIO, backgroundColor, tintColors); 69 } 70 71 /** 72 * 73 * Determines what color to tint icons given the background color that they sit on. 74 * 75 * @param minAllowedContrastRatio The minimum contrast ratio 76 * @param bgColor The background color that the icons sit on. 77 * @param tintColors A list of potential colors to tint the icons with. 78 * @return The color that the icons should be tinted. Will be the first tinted color that 79 * meets the requirements. If none of the tint colors meet the minimum requirements, 80 * either black or white will be returned, whichever has a higher contrast. 81 */ getTintColor(double minAllowedContrastRatio, int bgColor, int... tintColors)82 public static int getTintColor(double minAllowedContrastRatio, int bgColor, int... tintColors) { 83 for (int tc : tintColors) { 84 double contrastRatio = getContrastRatio(bgColor, tc); 85 if (contrastRatio >= minAllowedContrastRatio) { 86 return tc; 87 } 88 } 89 double blackContrastRatio = getContrastRatio(bgColor, Color.BLACK); 90 double whiteContrastRatio = getContrastRatio(bgColor, Color.WHITE); 91 if (whiteContrastRatio >= blackContrastRatio) { 92 Log.w(TAG, "Tint color does not meet contrast requirements. Using white."); 93 return Color.WHITE; 94 } else { 95 Log.w(TAG, "Tint color does not meet contrast requirements. Using black."); 96 return Color.BLACK; 97 } 98 } 99 getContrastRatio(int color1, int color2)100 public static double getContrastRatio(int color1, int color2) { 101 return getContrastRatio(getLuminance(color1), getLuminance(color2)); 102 } 103 getContrastRatio(double luminance1, double luminance2)104 public static double getContrastRatio(double luminance1, double luminance2) { 105 return (Math.max(luminance1, luminance2) + 0.05) / 106 (Math.min(luminance1, luminance2) + 0.05); 107 } 108 109 /** 110 * Calculates the luminance of a color as specified by: 111 * http://www.w3.org/TR/WCAG20-TECHS/G17.html 112 * 113 * @param color The color to calculate the luminance of. 114 * @return The luminance. 115 */ getLuminance(int color)116 public static double getLuminance(int color) { 117 // Values are in sRGB 118 double r = convert8BitToLuminanceComponent(Color.red(color)); 119 double g = convert8BitToLuminanceComponent(Color.green(color)); 120 double b = convert8BitToLuminanceComponent(Color.blue(color)); 121 return r * 0.2126 + g * 0.7152 + b * 0.0722; 122 } 123 124 /** 125 * Converts am 8 bit color component (0-255) to the luminance component as specified by: 126 * http://www.w3.org/TR/WCAG20-TECHS/G17.html 127 */ convert8BitToLuminanceComponent(double component)128 private static double convert8BitToLuminanceComponent(double component) { 129 component /= 255.0; 130 if (component <= 0.03928) { 131 return component / 12.92; 132 } else { 133 return Math.pow(((component + 0.055) / 1.055), 2.4); 134 } 135 } 136 } 137