misuzu/src/colour.php

<?php
define('MSZ_COLOUR_INHERIT', 0x40000000);
define('MSZ_COLOUR_READABILITY_THRESHOLD', 186);
define('MSZ_COLOUR_LUMINANCE_WEIGHT_RED', 0.299);
define('MSZ_COLOUR_LUMINANCE_WEIGHT_GREEN', 0.587);
define('MSZ_COLOUR_LUMINANCE_WEIGHT_BLUE', 0.114);

function colour_create(): int
{
    return 0;
}

function colour_none(): int
{
    return MSZ_COLOUR_INHERIT;
}

function colour_set_inherit(int &$colour, bool $enabled = true): void
{
    if ($enabled) {
        $colour |= MSZ_COLOUR_INHERIT;
    } else {
        $colour &= ~MSZ_COLOUR_INHERIT;
    }
}

function colour_get_inherit(int $colour): bool
{
    return ($colour & MSZ_COLOUR_INHERIT) > 0;
}

function colour_get_red(int $colour): int
{
    return ($colour >> 16) & 0xFF;
}

function colour_set_red(int &$colour, int $red): void
{
    $red = $red & 0xFF;
    $colour &= ~0xFF0000;
    $colour |= $red << 16;
}

function colour_get_green(int $colour): int
{
    return ($colour >> 8) & 0xFF;
}

function colour_set_green(int &$colour, int $green): void
{
    $green = $green & 0xFF;
    $colour &= ~0xFF00;
    $colour |= $green << 8;
}

function colour_get_blue(int $colour): int
{
    return $colour & 0xFF;
}

function colour_set_blue(int &$colour, int $blue): void
{
    $blue = $blue & 0xFF;
    $colour &= ~0xFF;
    $colour |= $blue;
}

function colour_get_luminance(int $colour): int
{
    return MSZ_COLOUR_LUMINANCE_WEIGHT_RED * colour_get_red($colour)
        + MSZ_COLOUR_LUMINANCE_WEIGHT_GREEN * colour_get_green($colour)
        + MSZ_COLOUR_LUMINANCE_WEIGHT_BLUE * colour_get_blue($colour);
}

function colour_get_hex(int $colour, string $format = '#%s'): string
{
    return sprintf(
        $format,
        dechex_pad($colour & 0xFFFFFF, 6)
    );
}

function colour_get_css(int $colour): string
{
    if (colour_get_inherit($colour)) {
        return 'inherit';
    }

    return colour_get_hex($colour);
}

function colour_get_css_contrast(
    int $colour,
    string $dark = 'dark',
    string $light = 'light',
    bool $inheritIsDark = true
): string {
    if (colour_get_inherit($colour)) {
        return $inheritIsDark ? $dark : $light;
    }

    return colour_get_luminance($colour) > MSZ_COLOUR_READABILITY_THRESHOLD
        ? $dark
        : $light;
}

function colour_from_rgb(int &$colour, int $red, int $green, int $blue): bool
{
    colour_set_red($colour, $red);
    colour_set_green($colour, $green);
    colour_set_blue($colour, $blue);
    return true;
}

function colour_from_hex(int &$colour, string $hex): bool
{
    if ($hex[0] === '#') {
        $hex = mb_substr($hex, 1);
    }

    $length = mb_strlen($hex);

    if ($length === 3) {
        $hex = $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
    } elseif ($length !== 6) {
        return false;
    }

    if (!ctype_xdigit($hex)) {
        return false;
    }

    colour_from_rgb(
        $colour,
        hexdec(mb_substr($hex, 0, 2)),
        hexdec(mb_substr($hex, 2, 2)),
        hexdec(mb_substr($hex, 4, 2))
    );

    return true;
}

function colour_get_properties(int $colour): array
{
    return [
        'red' => colour_get_red($colour),
        'green' => colour_get_green($colour),
        'blue' => colour_get_blue($colour),
        'inherit' => colour_get_inherit($colour),
        'luminance' => colour_get_luminance($colour),
    ];
}