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Bug #42434 ImageLine w/ antialias = 1px shorter
Submitted: 2007-08-27 04:50 UTC Modified: 2009-07-28 20:35 UTC
Votes:11
Avg. Score:4.5 ± 0.9
Reproduced:10 of 10 (100.0%)
Same Version:2 (20.0%)
Same OS:4 (40.0%)
From: wojjie at gmail dot com Assigned: pajoye
Status: Closed Package: GD related
PHP Version: 5.2.6 OS: *
Private report: No CVE-ID:
 [2007-08-27 04:50 UTC] wojjie at gmail dot com
Description:
------------
This bug looks fixed in the GD library, but for some reason the GD included in PHP still has this.

What happens is when drawing a line with anti aliasing enabled, the resulting line is 1 pixel shorter than it should be.

Fix (using snapshot: php5.2-200708270430.tar.gz):
--- gd.c       2007-08-26 23:44:04.000000000 -0500
+++ gd.c        2007-08-26 23:44:28.000000000 -0500
@@ -1351,7 +1351,7 @@
                x = x1 << 16;
                y = y1 << 16;
                inc = (dy * 65536) / dx;
-               while ((x >> 16) < x2) {
+               while ((x >> 16) <= x2) {
                        gdImageSetAAPixelColor(im, x >> 16, y >> 16, col, (y >> 8) & 0xFF);
                        if ((y >> 16) + 1 < im->sy) {
                                gdImageSetAAPixelColor(im, x >> 16, (y >> 16) + 1,col, (~y >> 8) & 0xFF);
@@ -1373,7 +1373,7 @@
                x = x1 << 16;
                y = y1 << 16;
                inc = (dx * 65536) / dy;
-               while ((y>>16) < y2) {
+               while ((y>>16) <= y2) {
                        gdImageSetAAPixelColor(im, x >> 16, y >> 16, col, (x >> 8) & 0xFF);
                        if ((x >> 16) + 1 < im->sx) {
                                gdImageSetAAPixelColor(im, (x >> 16) + 1, (y >> 16),col, (~x >> 8) & 0xFF);


Reproduce code:
---------------
<?php
$im=imagecreatetruecolor(30,30);

$c1=ImageColorAllocate($im,255,255,255);
$c2=ImageColorAllocate($im,  0,  0,  0);
imagefill( $im,0,0, $c1 );

imageline($im,5,5, 25,5, $c2);
imageantialias($im,true);
imageline($im,5,25, 25,25, $c2);

header("Content-type: image/png");
imagepng($im);
imagedestroy($im);

?>


Expected result:
----------------
Two lines of equal length

Actual result:
--------------
Top line is longer than bottom line by 1 pixel.

Patches

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Pull Requests

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History

AllCommentsChangesGit/SVN commitsRelated reports
 [2007-08-27 11:04 UTC] jani@php.net
Assigned to the maintainer.
 [2008-09-05 02:19 UTC] abc at abc dot abc
reproduced on PHP 5.2.6 / windows. problem is still there
 [2009-07-28 20:35 UTC] svn@php.net
Automatic comment from SVN on behalf of kalle
Revision: http://svn.php.net/viewvc/?view=revision&revision=286466
Log: Fixed bug #42434 (ImageLine w/ antialias = 1px shorter)
 - patch by wojjie at gmail dot com
 [2009-07-28 20:35 UTC] kalle@php.net
This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.


 [2009-07-30 03:54 UTC] svn@php.net
Automatic comment from SVN on behalf of kalle
Revision: http://svn.php.net/viewvc/?view=revision&revision=286540
Log: Test case for bug #42434
 
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