How to save RGB(A) values in an array?

Question

I'm trying to write a function that will take an RGB(A) color and save its values in an array, with an option to exclude the alpha value. I'm having trouble figuring out how to write the regex that will match the input, but I'm thinking that something like this is what I'm looking for:

function rgb_array( $color, $include_alpha = true ) {

    $pattern = 'what goes here?';

    $color = preg_match( $pattern, $color, $matches);

    if ( $include_alpha == true && ! empty( $matches[4] ) ) {
        $color = array( $matches[1], $matches[2], $matches[3], $matches[4] );
    } else {
        $color = array( $matches[1], $matches[2], $matches[3] );
    }

    return $color;
}

I would like to be able to feed it any valid form of rgb/rgba:

rgb(0,0,0)
rgb(00,00,00)
rgb(0, 0, 0)
rgb(00, 00, 00)
rgba(0,0,0,0.5)
rgba(255, 255, 255, 1)
etc...

And have it produce an array:

[0] => '00', // red
[1] => '00', // green
[2] => '00', // blue
[3] => '1' // alpha only included if available and desired.

At the moment I'm able to accomplish this through str_replace:

$color  = 'rgb(12, 14, 85)';
$remove = array( 'rgb', 'a', '(', ')', ' ' );
$color  = str_replace( $remove, '', $color );
$color  = explode( ',', $color );

But it feels hacky and I can't find a good way to optionally include/exclude alpha.

Thanks for your help, and if there's a completely different approach than preg_match that would be better, I'm all ears.

Answer 1

Not only will my answer extract the substring values that you desire, it will additionally perform a reasonably high level of validation (not 100% perfect validation). I modified the pattern from https://stackoverflow.com/a/31245990/2943403 to more precisely serve this question. I trust you will find this answer to be accurate, elegant, and direct.

If you want to strip back / simplify the pattern, this will do: (Regex101 Demo)
~^rgba?\((\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([.\d]+))?\)$~

Code: (Demo w/ $include_alpha = true) (Demo w/ $include_alpha = false) (Regex101 Demo)

function rgb_array($color, $include_alpha = true) {
    $pattern = '~^rgba?\((25[0-5]|2[0-4]\d|1\d{2}|\d\d?)\s*,\s*(25[0-5]|2[0-4]\d|1\d{2}|\d\d?)\s*,\s*(25[0-5]|2[0-4]\d|1\d{2}|\d\d?)\s*(?:,\s*([01]\.?\d*?))?\)$~';

    if (!preg_match($pattern, $color, $matches)) {
        return [];  // disqualified / no match
    }

    return array_slice($matches, 1, $include_alpha ? 4 : 3);
}

$strings = [
    'rgb(0,0,0)',
    'rgb(00,00,00)',
    'rgb(0, 0, 0)',
    'donkey eggs',
    'rgb(00, 00, 00)',
    'rgba(0,0,0,0.5)',
    'rgba(255, 255, 255, 1)'
];

foreach ($strings as $string) {
    echo "Process: $string\n";
    var_export(rgb_array($string));
    echo "\n";
}

Output:

Process: rgb(0,0,0)
array (
  0 => '0',
  1 => '0',
  2 => '0',
)
Process: rgb(00,00,00)
array (
  0 => '00',
  1 => '00',
  2 => '00',
)
Process: rgb(0, 0, 0)
array (
  0 => '0',
  1 => '0',
  2 => '0',
)
Process: donkey eggs
array (
)
Process: rgb(00, 00, 00)
array (
  0 => '00',
  1 => '00',
  2 => '00',
)
Process: rgba(0,0,0,0.5)
array (
  0 => '0',
  1 => '0',
  2 => '0',
  3 => '0.5',
)
Process: rgba(255, 255, 255, 1)
array (
  0 => '255',
  1 => '255',
  2 => '255',
  3 => '1',
)

---

p.s. If you want to use preg_split() you can be far less specific about your pattern. Here's a one-liner for you. (Demo)

function rgb_array($color, $include_alpha = true) {
    return array_slice(preg_split('~[^\d.]+~', $color, -1, PREG_SPLIT_NO_EMPTY), 0, $include_alpha + 3);
}

Answer 2

If you want a regex solution, here it is:

rgba?\((\s?\d+),(\s?\d+),(\s?\d+)(?:,\s?(\d+(?:\.\d+)?))?\)

It matches 'rgb' at start, then an optional 'a' and a left parenthes, then it creates 3 similar groupes, matching an optinal White Space followed by one or more digits. The fourth Group is optional and will match one or more digits, optionally followed by a dot, and one or more digits.

The colors will be at index 1, 2, 3 and 4 (if avaiable).

Answer 3

You could use preg_split to split the string into its component parts. The regex splits the string at one of the leading rgba(, a , or the trailing ). The PREG_SPLIT_NO_EMPTY flag is used to avoid blank values in the output array.

$strings = array('rgb(0,0,0)',
'rgb(00,00,00)',
'rgb(0, 0, 0)',
'rgb(00, 00, 00)',
'rgba(0,0,0,0.5)',
'rgba(255, 255, 255, 1)');
foreach ($strings as $string) {
    print_r(preg_split('/rgba?\(\s*|\s*,\s*|\s*\)/', $string, -1, PREG_SPLIT_NO_EMPTY));
}

Output:

Array
(
    [0] => 0
    [1] => 0
    [2] => 0
)
Array
(
    [0] => 00
    [1] => 00
    [2] => 00
)
Array
(
    [0] => 0
    [1] => 0
    [2] => 0
)
Array
(
    [0] => 00
    [1] => 00
    [2] => 00
)
Array
(
    [0] => 0
    [1] => 0
    [2] => 0
    [3] => 0.5
)
Array
(
    [0] => 255
    [1] => 255
    [2] => 255
    [3] => 1
)

Answer 4

A bit improved explode solution:

function rgb_array($color, $include_alpha = true)
{
    $color = trim($color, 'rgba()');       # "rgba(255, 255, 255, 1)" => "255, 255, 255, 1"
    $color = str_replace(' ', '', $color); # "255, 255, 255, 1"       => "255,255,255,1"
    $color = explode(',', $color);         # "255,255,255,1"          => ["255", "255", "255", "1"]
    $color[] = 1;                          # add extra value to be sure that all parsed colors have transparency

    return array_slice($color, 0, 3 + $include_alpha); # length is 3 or 4, depends on $include_alpha value
}

You can also extract numbers from the string based on the fact that built-in PHP type cast to float and int removes extra chars from the string:

function rgb_array($color, $include_alpha = true)
{
    $array = array_map('floatval', explode(',', $color));
    $array[] = 1;

    return array_slice($array, 0, 3 + $include_alpha);
}