Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
/*
 * 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.
 */

import android.graphics.Color;

public class Main {
    private static final ThreadLocal<double[]> TEMP_ARRAY = new ThreadLocal<>();

    /**
     * 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(int foreground, 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);
    }

    /**
     * Composite two potentially translucent colors over each other and returns the result.
     */
    public static int compositeColors(int foreground, 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);
    }

    /**
     * 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>
     */
    public static double calculateLuminance(int color) {
        final double[] result = getTempDouble3Array();
        colorToXYZ(color, result);
        // Luminance is the Y component
        return result[1] / 100;
    }

    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);
    }

    private static double[] getTempDouble3Array() {
        double[] result = TEMP_ARRAY.get();
        if (result == null) {
            result = new double[3];
            TEMP_ARRAY.set(result);
        }
        return result;
    }

    public static void colorToXYZ(int color, double[] outXyz) {
        RGBToXYZ(Color.red(color), Color.green(color), Color.blue(color), outXyz);
    }

    public static void RGBToXYZ(int r, int g, int b, 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);
    }
}