This function doesn't exist on ImageMagick 7.
There is meant to be an explanation of what to use instead, but it apparently hasn't been written.
function matte($strokeColor, $fillColor, $backgroundColor, $paintType)
{
$draw = new \ImagickDraw();
$draw->setStrokeColor($strokeColor);
$draw->setFillColor($fillColor);
$draw->setStrokeWidth(2);
$draw->setFontSize(72);
$draw->matte(120, 120, $paintType);
$draw->rectangle(100, 100, 300, 200);
$imagick = new \Imagick();
$imagick->newImage(500, 500, $backgroundColor);
$imagick->setImageFormat("png");
$imagick->drawImage($draw);
header("Content-Type: image/png");
echo $imagick->getImageBlob();
}