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15 years ago
I wanted to draw a transparent GIF-image and show it on a page, at an angle specified in the URL:

<img src="image.php?angle=90" type="image/gif">



I used the native imagerotate() but at angles of 90, 180, etc. the old background colour would become non-transparent. Apparently, there's a bug somewhere in GD, and has been for ages.



My solution below:



<?php

$height = 100;

$width = 100;

$lsize= $width/2;

$angle= $_GET["angle"];



// avoid the bug:

if(($angle%90)==0)

  $angle+= 0.001;



$image_p = imagecreatetruecolor($width, $height);

$trans = imagecolorallocate($image_p, 254, 0, 0);

imagefill($image_p, 0, 0, $trans);

imagecolortransparent($image_p, $trans);



$black = imagecolorallocate($image_p, 1, 1, 1);

$red = imagecolorallocate($image_p, 255, 0, 0);

$white = imagecolorallocate($image_p, 255, 255, 255);



// draw something here

imageline($image_p, 3, $lsize, $lsize/2, $lsize, $black);



$image_r= imagerotate($image_p, -$angle, $trans, 0); 

$w= imagesx($image_r);

$h= imagesy($image_r);

$image_s = imagecreatetruecolor($width, $height);

imagecopyresized($image_s, $image_r, 0, 0, ($w-$width)/2, ($h-$height)/2, $width, $height, $width, $height);

$trans = imagecolorallocate($image_s, 254, 0, 0);

imagecolortransparent($image_s, $trans);

imagegif($image_s);

?>
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