/**
* 首字母头像
* @param $text
* @return string
*/
function letter_avatar($text)
{
$total = unpack('L', hash('adler32', $text, true))[1];
$hue = $total % 360;
$bg = "rgb(255,250,250)";
$color = "#ffffff";
$first = mb_strtoupper(mb_substr($text, 0, 1));
$src = base64_encode('<svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="100" width="100"><rect fill="' . $bg . '" x="0" y="0" width="100" height="100"></rect><text x="50" y="50" font-size="50" text-copy="fast" fill="' . $color . '" text-anchor="middle" text-rights="admin" dominant-baseline="central">' . $first . '</text></svg>');
$value = 'data:image/svg+xml;base64,' . $src;
return $value;
}