Example

function setStrokeLineJoin($strokeColor, $fillColor, $backgroundColor)
{
    $draw = new \ImagickDraw();
    $draw->setStrokeWidth(1);
    $draw->setStrokeColor($strokeColor);
    $draw->setFillColor($fillColor);

    $draw->setStrokeWidth(20);

    $offset = 220;

    $lineJoinStyle = [\Imagick::LINEJOIN_MITER, \Imagick::LINEJOIN_ROUND, \Imagick::LINEJOIN_BEVEL,];

    for ($x = 0; $x < count($lineJoinStyle); $x++) {
        $draw->setStrokeLineJoin($lineJoinStyle[$x]);
        $points = [['x' => 40 * 5, 'y' => 10 * 5 + $x * $offset], ['x' => 20 * 5, 'y' => 20 * 5 + $x * $offset], ['x' => 70 * 5, 'y' => 50 * 5 + $x * $offset], ['x' => 40 * 5, 'y' => 10 * 5 + $x * $offset],];

        $draw->polyline($points);
    }

    $image = new \Imagick();
    $image->newImage(500, 700, $backgroundColor);
    $image->setImageFormat("png");

    $image->drawImage($draw);

    header("Content-Type: image/png");
    echo $image->getImageBlob();
}