polyline auto-closes - how to draw an open polyline? - php

Question

I'm in need of drawing continuous lines in PHP. GD apparently can't do it, but imagick has a polyline function. Now my test code:
$image = new Imagick();
$image->newImage(100, 100, new ImagickPixel('white'));
$draw = new ImagickDraw();
$draw->setStrokeWidth(3);
$line = array(
array('x'=>10, 'y'=>10),
array('x'=>50, 'y'=>10),
array('x'=>70, 'y'=>40),
array('x'=>30, 'y'=>60),
);
$draw->polyline($line);
$image->drawImage($draw);
$image->setImageFormat('jpg');
$image->writeImage("test.jpg");
produces a CLOSED (and filled) polygon for reasons I can't fathom. What's going on here and how do I fix it? I want it to stop at the last point and NOT close or fill.
If there's a solution in GD, I'm also happy. No, I can't simply string individual lines together, because I want thickness in the lines.

Answer 1

It is possible to draw an open polyline by drawing in one direction and then back with the same points table, without first and last point (they are not neccessary)
so, if you have
$line = array(
array('x'=>10, 'y'=>10),
array('x'=>50, 'y'=>10),
array('x'=>70, 'y'=>40),
array('x'=>30, 'y'=>60),
);
you should add
$line[] = array('x'=>70, 'y'=>40);
$line[] = array('x'=>50, 'y'=>10);
and then
$draw->polyline($line);
and you would get what you want.

Answer 2

Looks at the documentation of GD polyline. Perhaps it that you want : http://bonzoli.com/sourcecode/index.php/man/GD::Polyline

Answer 3

You should define both the stroke and fill colors, otherwise Imagick will "fill" the area bounded by the line and the start and finish points with the fill color. The defaults are for these values are "white" and "black".
This code will work as intended, i.e. it produces a mirrored "c" shaped object with black lines of 3 pixels width:
$image = new Imagick();
$image->newImage(100, 100, 'white');
$draw = new ImagickDraw();
$draw->setStrokeWidth(3);
$draw->setStrokeColor ("black");
$draw->setFillColor ("none");
$line = array(
array('x'=>10, 'y'=>10),
array('x'=>50, 'y'=>10),
array('x'=>70, 'y'=>40),
array('x'=>30, 'y'=>60),
);
$draw->polyline($line);
$image->drawImage($draw);
$image->writeImage("test.jpg");