android/graphics/Color.java

/*
 * Copyright (C) 2006 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.graphics;

import android.annotation.ColorInt;
import android.annotation.Size;

import com.android.internal.util.XmlUtils;

import java.util.HashMap;
import java.util.Locale;
import java.util.function.DoubleUnaryOperator;

/**
 * The Color class defines methods for creating and converting color ints.
 * Colors are represented as packed ints, made up of 4 bytes: alpha, red,
 * green, blue. The values are unpremultiplied, meaning any transparency is
 * stored solely in the alpha component, and not in the color components. The
 * components are stored as follows (alpha << 24) | (red << 16) |
 * (green << 8) | blue. Each component ranges between 0..255 with 0
 * meaning no contribution for that component, and 255 meaning 100%
 * contribution. Thus opaque-black would be 0xFF000000 (100% opaque but
 * no contributions from red, green, or blue), and opaque-white would be
 * 0xFFFFFFFF
 */
public class Color {
    @ColorInt public static final int BLACK       = 0xFF000000;
    @ColorInt public static final int DKGRAY      = 0xFF444444;
    @ColorInt public static final int GRAY        = 0xFF888888;
    @ColorInt public static final int LTGRAY      = 0xFFCCCCCC;
    @ColorInt public static final int WHITE       = 0xFFFFFFFF;
    @ColorInt public static final int RED         = 0xFFFF0000;
    @ColorInt public static final int GREEN       = 0xFF00FF00;
    @ColorInt public static final int BLUE        = 0xFF0000FF;
    @ColorInt public static final int YELLOW      = 0xFFFFFF00;
    @ColorInt public static final int CYAN        = 0xFF00FFFF;
    @ColorInt public static final int MAGENTA     = 0xFFFF00FF;
    @ColorInt public static final int TRANSPARENT = 0;

    /**
     * Return the alpha component of a color int. This is the same as saying
     * color >>> 24
     */
    public static int alpha(int color) {
        return color >>> 24;
    }

    /**
     * Return the red component of a color int. This is the same as saying
     * (color >> 16) & 0xFF
     */
    public static int red(int color) {
        return (color >> 16) & 0xFF;
    }

    /**
     * Return the green component of a color int. This is the same as saying
     * (color >> 8) & 0xFF
     */
    public static int green(int color) {
        return (color >> 8) & 0xFF;
    }

    /**
     * Return the blue component of a color int. This is the same as saying
     * color & 0xFF
     */
    public static int blue(int color) {
        return color & 0xFF;
    }

    /**
     * Return a color-int from red, green, blue components.
     * The alpha component is implicity 255 (fully opaque).
     * These component values should be [0..255], but there is no
     * range check performed, so if they are out of range, the
     * returned color is undefined.
     * @param red  Red component [0..255] of the color
     * @param green Green component [0..255] of the color
     * @param blue  Blue component [0..255] of the color
     */
    @ColorInt
    public static int rgb(int red, int green, int blue) {
        return 0xff000000 | (red << 16) | (green << 8) | blue;
    }

    /**
     * Return a color-int from alpha, red, green, blue components.
     * These component values should be [0..255], but there is no
     * range check performed, so if they are out of range, the
     * returned color is undefined.
     * @param alpha Alpha component [0..255] of the color
     * @param red   Red component [0..255] of the color
     * @param green Green component [0..255] of the color
     * @param blue  Blue component [0..255] of the color
     */
    @ColorInt
    public static int argb(int alpha, int red, int green, int blue) {
        return (alpha << 24) | (red << 16) | (green << 8) | blue;
    }

    /**
     * Returns the relative luminance of a color.
     * <p>
     * Assumes sRGB encoding. Based on the formula for relative luminance
     * defined in WCAG 2.0, W3C Recommendation 11 December 2008.
     *
     * @return a value between 0 (darkest black) and 1 (lightest white)
     */
    public static float luminance(@ColorInt int color) {
        ColorSpace.Rgb cs = (ColorSpace.Rgb) ColorSpace.get(ColorSpace.Named.SRGB);
        DoubleUnaryOperator eotf = cs.getEotf();
        double red = eotf.applyAsDouble(Color.red(color) / 255.0);
        double green = eotf.applyAsDouble(Color.green(color) / 255.0);
        double blue = eotf.applyAsDouble(Color.blue(color) / 255.0);
        return (float) ((0.2126 * red) + (0.7152 * green) + (0.0722 * blue));
    }

    /**
     * Parse the color string, and return the corresponding color-int.
     * If the string cannot be parsed, throws an IllegalArgumentException
     * exception. Supported formats are:
     * #RRGGBB
     * #AARRGGBB
     * or one of the following names:
     * 'red', 'blue', 'green', 'black', 'white', 'gray', 'cyan', 'magenta',
     * 'yellow', 'lightgray', 'darkgray', 'grey', 'lightgrey', 'darkgrey',
     * 'aqua', 'fuchsia', 'lime', 'maroon', 'navy', 'olive', 'purple',
     * 'silver', 'teal'.
     */
    @ColorInt
    public static int parseColor(@Size(min=1) String colorString) {
        if (colorString.charAt(0) == '#') {
            // Use a long to avoid rollovers on #ffXXXXXX
            long color = Long.parseLong(colorString.substring(1), 16);
            if (colorString.length() == 7) {
                // Set the alpha value
                color |= 0x00000000ff000000;
            } else if (colorString.length() != 9) {
                throw new IllegalArgumentException("Unknown color");
            }
            return (int)color;
        } else {
            Integer color = sColorNameMap.get(colorString.toLowerCase(Locale.ROOT));
            if (color != null) {
                return color;
            }
        }
        throw new IllegalArgumentException("Unknown color");
    }

    /**
     * Convert RGB components to HSV.
     *     hsv[0] is Hue [0 .. 360)
     *     hsv[1] is Saturation [0...1]
     *     hsv[2] is Value [0...1]
     * @param red  red component value [0..255]
     * @param green  green component value [0..255]
     * @param blue  blue component value [0..255]
     * @param hsv  3 element array which holds the resulting HSV components.
     */
    public static void RGBToHSV(int red, int green, int blue, @Size(3) float hsv[]) {
        if (hsv.length < 3) {
            throw new RuntimeException("3 components required for hsv");
        }
        nativeRGBToHSV(red, green, blue, hsv);
    }

    /**
     * Convert the argb color to its HSV components.
     *     hsv[0] is Hue [0 .. 360)
     *     hsv[1] is Saturation [0...1]
     *     hsv[2] is Value [0...1]
     * @param color the argb color to convert. The alpha component is ignored.
     * @param hsv  3 element array which holds the resulting HSV components.
     */
    public static void colorToHSV(@ColorInt int color, @Size(3) float hsv[]) {
        RGBToHSV((color >> 16) & 0xFF, (color >> 8) & 0xFF, color & 0xFF, hsv);
    }

    /**
     * Convert HSV components to an ARGB color. Alpha set to 0xFF.
     *     hsv[0] is Hue [0 .. 360)
     *     hsv[1] is Saturation [0...1]
     *     hsv[2] is Value [0...1]
     * If hsv values are out of range, they are pinned.
     * @param hsv  3 element array which holds the input HSV components.
     * @return the resulting argb color
    */
    public static int HSVToColor(@Size(3) float hsv[]) {
        return HSVToColor(0xFF, hsv);
    }

    /**
     * Convert HSV components to an ARGB color. The alpha component is passed
     * through unchanged.
     *     hsv[0] is Hue [0 .. 360)
     *     hsv[1] is Saturation [0...1]
     *     hsv[2] is Value [0...1]
     * If hsv values are out of range, they are pinned.
     * @param alpha the alpha component of the returned argb color.
     * @param hsv  3 element array which holds the input HSV components.
     * @return the resulting argb color
    */
    public static int HSVToColor(int alpha, @Size(3) float hsv[]) {
        if (hsv.length < 3) {
            throw new RuntimeException("3 components required for hsv");
        }
        return nativeHSVToColor(alpha, hsv);
    }

    private static native void nativeRGBToHSV(int red, int greed, int blue, float hsv[]);
    private static native int nativeHSVToColor(int alpha, float hsv[]);

    /**
     * Converts an HTML color (named or numeric) to an integer RGB value.
     *
     * @param color Non-null color string.
     *
     * @return A color value, or {@code -1} if the color string could not be interpreted.
     *
     * @hide
     */
    @ColorInt
    public static int getHtmlColor(String color) {
        Integer i = sColorNameMap.get(color.toLowerCase(Locale.ROOT));
        if (i != null) {
            return i;
        } else {
            try {
                return XmlUtils.convertValueToInt(color, -1);
            } catch (NumberFormatException nfe) {
                return -1;
            }
        }
    }

    private static final HashMap<String, Integer> sColorNameMap;
    static {
        sColorNameMap = new HashMap<>();
        sColorNameMap.put("black", BLACK);
        sColorNameMap.put("darkgray", DKGRAY);
        sColorNameMap.put("gray", GRAY);
        sColorNameMap.put("lightgray", LTGRAY);
        sColorNameMap.put("white", WHITE);
        sColorNameMap.put("red", RED);
        sColorNameMap.put("green", GREEN);
        sColorNameMap.put("blue", BLUE);
        sColorNameMap.put("yellow", YELLOW);
        sColorNameMap.put("cyan", CYAN);
        sColorNameMap.put("magenta", MAGENTA);
        sColorNameMap.put("aqua", 0xFF00FFFF);
        sColorNameMap.put("fuchsia", 0xFFFF00FF);
        sColorNameMap.put("darkgrey", DKGRAY);
        sColorNameMap.put("grey", GRAY);
        sColorNameMap.put("lightgrey", LTGRAY);
        sColorNameMap.put("lime", 0xFF00FF00);
        sColorNameMap.put("maroon", 0xFF800000);
        sColorNameMap.put("navy", 0xFF000080);
        sColorNameMap.put("olive", 0xFF808000);
        sColorNameMap.put("purple", 0xFF800080);
        sColorNameMap.put("silver", 0xFFC0C0C0);
        sColorNameMap.put("teal", 0xFF008080);

    }
}