php image arrow line need to be smooth

Question

im making a line in php and so far its showing fine, but what problem im getting now is the line is not being smooth, it shows as breaking edges. following is the code for making radius line:

function draw_radius($img, $x1, $y1, $radius, $angle, $arrow_color, $arrow_length = 10, $arrow_width = 3)
{
    $x2 = $x1 + $radius * cos(deg2rad($angle-90));
    $y2 = $y1 + $radius * sin(deg2rad($angle-90));
    imageline($img, $x1, $y1, $x2, $y2, $arrow_color);

    $distance = sqrt(pow($x1 - $x2, 2) + pow($y1 - $y2, 2));
    $dx = $x2 + ($x1 - $x2) * $arrow_length / $distance;
    $dy = $y2 + ($y1 - $y2) * $arrow_length / $distance;
    $k = $arrow_width / $arrow_length;
    $x2o = $x2 - $dx;
    $y2o = $dy - $y2;
    $x3 = $y2o * $k + $dx;
    $y3 = $x2o * $k + $dy;
    $x4 = $dx - $y2o * $k;
    $y4 = $dy - $x2o * $k;
    imageline($img, $x1, $y1, $dx, $dy, $arrow_color);
    imageline($img, $x3, $y3, $x4, $y4, $arrow_color);
    imageline($img, $x3, $y3, $x2, $y2, $arrow_color);
    imageline($img, $x2, $y2, $x4, $y4, $arrow_color);


}

following is the compass example, which im drawing line on.

Answer 1

You need to use an image processing library that has anti-aliasing. For an explanation of the technique, see http://en.wikipedia.org/wiki/Anti_aliasing. I have no suggestions for which library you should use; I don't use PHP for image processing.

Answer 2

You could try this, but going by their example, it doesn't seem great. There are a few other options you could try in the comments.

Answer 3

Haven't tried anti-aliasing in GD myself, but it appears to be there...

http://uk.php.net/manual/en/function.imageantialias.php

Answer 4

cairo does antialiasing well.