Bug #55005 [Ver]: imagepolygon, imagefilledpolygon num_points requirement

Edit report at https://bugs.php.net/bug.php?id=55005&edit=1 ID: 55005 Updated by: cmb@php.net Reported by: lbayuk at users dot sourceforge dot net Summary: imagepolygon, imagefilledpolygon num_points requirement Status: Verified Type: Bug Package: GD related Operating System: n/a PHP Version: 5.3.6 -Assigned To: +Assigned To: cmb Block user comment: N Private report: N New Comment: FTR: I've just emailed the internals list: <http://news.php.net/php.internals/97915>. Previous Comments: ------------------------------------------------------------------------ [2015-07-13 18:21:37] cmb@php.net Gee! It seems to me the cleanest solution would be to get rid of the $num_points parameter altogether, and to only check for an even number of array elements (and maybe for a minimum count). Of course, that would be a major BC break, and so is out of scope before PHP 8, at least. Should we rely on gdImage(Filled)Polygon() to behave reasonably for 1 and 2 points? The libgd implementation might change sometime to require at least 3 points, and anyway, monogons and digons are usually not recognized as polygons. So probably we shouldn't. To avoid any BC breaks for PHP 5, I suggest to only document that imagepolygon must have at least 3 vertices, but not to enforce that in the code. For PHP 7 it seems to make sense to actually check for $num_points >= 3; see the attached patch. ------------------------------------------------------------------------ [2015-07-13 18:19:48] cmb@php.net The following patch has been added/updated: Patch Name: imagepolygon-numpoints Revision: 1436811588 URL: https://bugs.php.net/patch-display.php?bug=55005&patch=imagepolygon-numpoints&revision=1436811588 ------------------------------------------------------------------------ [2015-06-22 22:03:06] lbayuk at users dot sourceforge dot net Verified still there in PHP-5.6.10 ------------------------------------------------------------------------ [2011-06-06 23:26:43] lbayuk at users dot sourceforge dot net Description: ------------ The gd extension function imagepolygon() requires at least 3 points. While this restriction is documented for imagefilledpolygon(), it is not documented for imagepolygon(). Since both are implemented with the same function php_imagepolygon() and contain the same check, the documentation for imagepolygon() should be updated to match imagefilledpolygon() in requiring at least 3 points. However, this is not just a documentation problem. The implementation does not actually check for num_points >= 3 as the documentation for imagefilledpolygon says. It checks that the points array size is at least 6 (3 points, 2 values each). So you can plot a 2-point or even 1-point filled or unfilled polygon, if you use an array with 3 or more points in it but specify num_points=2 or 1. This is very strange, not working as documented, and surely not as intended. But there's more. As far as I can tell, libgd (bundled or stand-alone) doesn't actually have a 3-point minimum restriction to gdImagePolygon() or gdImageFilledPolygon(), although it does seem to be documented. See the sample code below, which plots 2-point filled and unfilled polygons by using the above trick. It also works with num_points=1. If true, the PHP check for 3 or more points is not needed at all. Test script: --------------- <?php # Plot illegal 2-point polygon and filled polygon using over-sized array. $g = imagecreate(300, 300); $bgnd = imagecolorallocate($g, 255, 255, 255); $fgnd = imagecolorallocate($g, 0, 0, 0); imagefilledpolygon($g, array(100,10, 100,100, 180,100), 2, $fgnd); imagepolygon($g, array(200,10, 200,100, 280,100), 2, $fgnd); imagepng($g); Expected result: ---------------- An error, since num_points=2 is not valid per documentation of ImageFilledPolygon. Actual result: -------------- A PNG image with 2 lines (2-point polygons). ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=55005&edit=1