ID: 22103 Updated by: [EMAIL PROTECTED] Reported By: [EMAIL PROTECTED] -Status: Open +Status: Verified Bug Type: GD related Operating System: Linux PHP Version: 4.3.0 New Comment:
Hello, Thank's for the report. <Since I'm doing a lot of graphic stuff I'll see if I can come up with a new algorithm to do this. I'm afraid however that any correct algortihm will be quite CPU expensive.> I have already solved this problem with a quit nice and fast algorithm. I have to check if I can add it to the current 4_3 HEAD. Doing something better with ellipse then what GD currently does is not very difficult (actually it's nothing else than a filled polygon with many connected lines, kind of ugly things to draw a simple ellipse). pierre Previous Comments: ------------------------------------------------------------------------ [2003-02-07 11:06:00] [EMAIL PROTECTED] I had a look in the source in GD. The problem is the way the gdImageFilledArc() is implemented. The algorithm there is flawed for alpha-blending. It fills the arc by drawing a series of filled polygons (triangles) centerd in the middle of the ellipse and out to the edge of the ellipse with 1 degree separation between the end points. This will make the interior points overlap and create the moire pattern. Unfortunately there isn't a simple solution to this. Doing a floodfill to a specific color wan't work since we don't know the canvas we are drawing on. Since I'm doing a lot of graphic stuff I'll see if I can come up with a new algorithm to do this. I'm afraid however that any correct algortihm will be quite CPU expensive. ------------------------------------------------------------------------ [2003-02-07 09:44:44] [EMAIL PROTECTED] The problem still exist in snapshot 200302071430. I haven't had time to look at the GD code but this is most likely a design flaw and not a straight bug. Fixing this will probably require a new fill algorithm for ellipses that can guarantee that the same pixel inside the ellipse will only be painted exactly one time. The script below demonstrates this bug and the resulting image can also be viewed at http://www.aditus.nu/jpgraph/bbimages/filledellipsebug.png <?php header("Content-type: image/png"); // Create a truecolor image with alpha blending $im = imagecreatetruecolor(200,200); imagealphablending ($im,true); // Background color $bkg = imagecolorresolvealpha($im, 255,255,255,0); // Red with ~70% alpha blending (90/127) $red = imagecolorresolvealpha($im, 255,0,0,90); // White background imagefilledrectangle($im,0,0,200,200,$bkg); // Filled circle (with moire' patterns) imagefilledellipse($im,100,100,120,120,$red); imagepng($im); imagedestroy($im); ?> ------------------------------------------------------------------------ [2003-02-07 06:36:22] [EMAIL PROTECTED] Please try using this CVS snapshot: http://snaps.php.net/php4-STABLE-latest.tar.gz For Windows: http://snaps.php.net/win32/php4-win32-STABLE-latest.zip There were couple of fixes in GD in CVS. If it still fails, please provide a short example script. ------------------------------------------------------------------------ [2003-02-06 22:18:03] [EMAIL PROTECTED] (Using built-in GD 2.x in PHP 4.3.0) imagefilledellipse() creates moire' patterns inside the filled ellipse when alpha blending is enabled. The problem seems to be that the fill algorithm strokes the same point within the ellipse several times and due to the alpha blending of single pixels creates several color shades within the ellipse. This is fine as long as a solid fill is used but does not work together with alpha blending. ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=22103&edit=1
