(PHP 4, PHP 5, PHP 7)
imagearc — Draws an arc
$image
   , int $cx
   , int $cy
   , int $width
   , int $height
   , int $start
   , int $end
   , int $color
   )imagearc() draws an arc of circle centered at the given coordinates.
imageAn image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
cxx-coordinate of the center.
cyy-coordinate of the center.
widthThe arc width.
heightThe arc height.
startThe arc start angle, in degrees.
endThe arc end angle, in degrees. 0° is located at the three-o'clock position, and the arc is drawn clockwise.
colorA color identifier created with imagecolorallocate().
   Returns TRUE on success or FALSE on failure.
  
Example #1 Drawing a circle with imagearc()
<?php
// create a 200*200 image
$img = imagecreatetruecolor(200, 200);
// allocate some colors
$white = imagecolorallocate($img, 255, 255, 255);
$red   = imagecolorallocate($img, 255,   0,   0);
$green = imagecolorallocate($img,   0, 255,   0);
$blue  = imagecolorallocate($img,   0,   0, 255);
// draw the head
imagearc($img, 100, 100, 200, 200,  0, 360, $white);
// mouth
imagearc($img, 100, 100, 150, 150, 25, 155, $red);
// left and then the right eye
imagearc($img,  60,  75,  50,  50,  0, 360, $green);
imagearc($img, 140,  75,  50,  50,  0, 360, $blue);
// output image in the browser
header("Content-type: image/png");
imagepng($img);
// free memory
imagedestroy($img);
?>
The above example will output something similar to:
