Strange php behaviour on a gd function

i met a very strange PHP behaviour, i don't understand why it behaves like this. I'm using the imagesetbrush function in this way:

class foo
{
   function setbrush($image)
   {
       //$this->_resource contains the main image resource
       imagesetbrush($this->_resource, $image);
   }
}
...
$res=imagecreatefrompng("image.png");
$class->setbrush($开发者_StackOverflow社区res);

in this way it works, but if i change the code like this:

class foo
{
   function setbrush($image)
   {
       $res=imagecreatefrompng($image);
       imagesetbrush($this->_resource, $res);
   }
}
...
$class->setbrush("image.png");

it doesn't work anymore. Do you see some error? It doesn't show me any message it simply doesn't execute the function.

Could it be that the reference to the variable $res disappears after the function call? Have you tried declaring it as a class variable, just like the $_resource variable?

Maybe somewhere in your foo class the working directory changes, so it can no longer find the image.png maybe when opening //$this->_resource contains the main image resource