Color.php

<?php
/* Copyright (c) 2017 Nils Haagen <nils.haagen@concepts-and-training.de> Extended GPL, see docs/LICENSE */

namespace ILIAS\Data;

/**
 * Color expresses a certain color by giving the mixing ratio
 * in the RGB color space.
 *
 * @author Nils Haagen <nils.haagen@concepts-and-training.de>
 */
class Color
{

    /**
     * @var integer
     */
    protected $r;

    /**
     * @var integer
     */
    protected $g;

    /**
     * @var integer
     */
    protected $b;


    public function __construct($r, $g, $b)
    {
        if (!is_integer($r) or $r < 0 || $r > 255) {
            throw new \InvalidArgumentException("Unexpected value for \$r: '$r'");
        }
        if (!is_integer($g) or $g < 0 || $g > 255) {
            throw new \InvalidArgumentException("Unexpected value for \$g: '$g'");
        }
        if (!is_integer($b) or $b < 0 || $b > 255) {
            throw new \InvalidArgumentException("Unexpected value for \$b: '$b'");
        }
        $this->r = $r;
        $this->g = $g;
        $this->b = $b;
    }

    /**
     * Get the valule for red.
     *
     * @return integer
     */
    public function r()
    {
        return $this->r;
    }
    /**
     * Get the valule for green.
     *
     * @return integer
     */
    public function g()
    {
        return $this->g;
    }
    /**
     * Get the valule for blue.
     *
     * @return integer
     */
    public function b()
    {
        return $this->b;
    }

    /**
     * Return array with RGB-values.
     *
     * @return int[]
     */
    public function asArray()
    {
        return array(
            $this->r,
            $this->g,
            $this->b
        );
    }

    /**
     * Return color-value in hex-format.
     *
     * @return string
     */
    public function asHex()
    {
        $hex = '#';
        foreach ($this->asArray() as $value) {
            $hex .= str_pad(dechex($value), 2, '0', STR_PAD_LEFT);
        }
        return $hex;
    }

    /**
     * Return string with RGB-notation
     *
     * @return string
     */
    public function asRGBString()
    {
        return 'rgb('
            . implode(', ', $this->asArray())
            . ')';
    }

    /**
    * Based on https://de.wikipedia.org/wiki/Luminanz
    * this function decides if the color can be considered "dark".
    * With a dark background, i.e., a lighter (white) color should be used
    * for the foreground.
    *
    * @return boolean
    */
    public function isDark()
    {
        $sum = 0.299 * $this->r + 0.587 * $this->g + 0.114 * $this->b;
        if ($sum < 128) {
            return true;
        }
        return false;
    }
}