(PHP 7 >= 7.2.0, PHP 8)
imageopenpolygon — Draws an open polygon
Signature as of PHP 8.0.0 (not supported with named arguments)
Alternative signature (deprecated as of PHP 8.1.0)
   imageopenpolygon() draws an open polygon on the given
   image. Contrary to imagepolygon(),
   no line is drawn between the last and the first point.
  
imageA GdImage object, returned by one of the image creation functions, such as imagecreatetruecolor().
pointsAn array containing the polygon's vertices, e.g.:
| points[0] | = x0 | 
| points[1] | = y0 | 
| points[2] | = x1 | 
| points[3] | = y1 | 
num_pointsTotal number of points (vertices), which must be at least 3.
If this parameter is omitted as per the second signature,points
       must have an even number of elements, and num_points is
       assumed to be count($points)/2.
      
     colorA color identifier created with imagecolorallocate().
   Returns true on success or false on failure.
  
| Version | Description | 
|---|---|
| 8.1.0 | The parameter num_pointshas been deprecated. | 
| 8.0.0 | imageexpects a GdImage
  instance now; previously, a validgdresource was expected. | 
Example #1 imageopenpolygon() example
<?php
// Create a blank image
$image = imagecreatetruecolor(400, 300);
// Allocate a color for the polygon
$col_poly = imagecolorallocate($image, 255, 255, 255);
// Draw the polygon
imageopenpolygon($image, array(
        0,   0,
        100, 200,
        300, 200
    ),
    3,
    $col_poly);
// Output the picture to the browser
header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>
The above example will output something similar to:
