(PECL imagick 2.0.0)
ImagickDraw::setStrokeLineJoin — Specifies the shape to be used at the corners of paths when they are stroked
$linejoin
   )This function is currently not documented; only its argument list is available.
Specifies the shape to be used at the corners of paths (or other vector shapes) when they are stroked.
linejoinLINEJOIN_ constant
No value is returned.
Example #1 ImagickDraw::setStrokeLineJoin()
<?php
function setStrokeLineJoin($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();
}
?>