For many (myself included) Rex's note maybe not be blatant enough. The constants are declared for the Imagick class only, so using them requires this syntax: Imagick::LINEJOIN_ constant
Here's an example oh how you might use it:
$img = new Imagick();
$img->newImage($width, $height, new ImagickPixel('transparent'));
$draw = new ImagickDraw();
If you're not drawing polylines and are drawing simple lines, also see setStrokeLineCap
(PECL imagick 2.0.0)
ImagickDraw::setStrokeLineJoin — Specifies the shape to be used at the corners of paths when they are stroked
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.
No value is returned.