PHP Opacity multiplication

Question

So I have a string like this "rgba(66, 66, 66, 1)" how could I multiply the last digit or number of it by 255. It would also need to be compliant with rgba(214, 234, 216, 0.6) for example. I wasnt sure how to do this as the rgb aspect and the opacity could be different every time.

Answer 1

Here is a working function that parses the rgba format and returns an array with each color, along with scaling a float alpha value out to 0-255. It also clamps all the values between 0-255 to prevent overflows outside that range. If an invalid rgb string is passed in, the function returns false.

Function (demo):

/**
 * Parses an RGBA string and returns and array with each color
 * @param  string $str The RGBA string, ex: "rgba(66, 66, 66, 1)"
 * @return array       Returns an array with each r, g, b and a value or false if an invalid string is passed in.
 */
function parseRGBA($str){
    //match the rgba string and get it's part
    if(preg_match('/rgba\( *([\d\.-]+), *([\d\.-]+), *([\d\.-]+), *([\d\.-]+) *\)/i', $str, $m)){
        $out = array(
            'r'=>intval($m[1]), //get the red
            'g'=>intval($m[2]), //get the green
            'b'=>intval($m[3]), //get the blue
            'a'=>round(floatval($m[4]) * 255), //get the alpha and scale to 0-255
        );

        //clamp each  value between 0 and 255
        array_walk($out, function(&$v){ $v = min(255, max(0, $v)); });

        return $out;
    }
    return false;
}

Example:

echo '<pre>';
echo "Normal value: ";
print_r(parseRGBA("rgba(66, 66, 66, 1)"));

echo "Red > 255: ";
print_r(parseRGBA("rgba(660, 66, 66, 1)"));

echo "Green < 0: ";
print_r(parseRGBA("rgba(66, -66, 66, 1)"));

echo "Alpha float (normal): ";
print_r(parseRGBA("rgba(66, 66, 66, 0.6)"));

echo "Alpha overflow: ";
print_r(parseRGBA("rgba(66, 66, 66, 10)"));

outputs:

Normal value: Array
(
    [r] => 66
    [g] => 66
    [b] => 66
    [a] => 255
)
Red > 255: Array
(
    [r] => 255
    [g] => 66
    [b] => 66
    [a] => 255
)
Green < 0: Array
(
    [r] => 66
    [g] => 0
    [b] => 66
    [a] => 255
)
Alpha float (normal): Array
(
    [r] => 66
    [g] => 66
    [b] => 66
    [a] => 153
)
Alpha overflow: Array
(
    [r] => 66
    [g] => 66
    [b] => 66
    [a] => 255
)