@codemasher Hey there again! Could I may ask, if there is an option to exclude some modules from being drawn as the custom shape I defined? Currently I've overwritten the module() method to draw a rhombus-like shape and literally everything will be drawn like that. But I want to draw everything else (especially the finders and their dots) as usual squares.

Hey, I think this is what you're looking for (see also #150):

My biggest respect and gratitude that you answer so fast. You seem very dedicated in this wonderful masterpiece of a library! Thank you for your answer! At the same time I have to apologize. I wasted your time, because before you answered I continued searching for an answer myself of course and found the exact same code you just referred to. ^^'
I'm a junior dev, completely new to php (3 months of experience in that language) coming from the C# world so please forgive me my unexperience.

But that leads me to another question. I just used that, but obviously now it's just skipping the finders and leaves them blank (white/not visible). I don't really understand where I can define them to be usual squares.

Well we all started at some point haha. Glad to be of help - it's nothing really.

I don't really understand where I can define them to be usual squares.

You just take the bit above that checks for the finder patterns and put it into another if(...) and return the square blocks there.
Basically:

// light module (return empty)
if(!$this->drawLightModules && !$this->matrix->isDark($M_TYPE)){ 
 return ''; 
}
// determine position as in the EPS output class
// ...
// return square shape for the given types
if($this->matrix->checkType($x, $y, QRMatrix::M_FINDER) || $this->matrix->checkType($x, $y, QRMatrix::M_FINDER_DOT)){
 return sprintf('%d %d %d %d F', $outputX, $outputY, $this->scale, $this->scale);
}
// return custom shape
return '...';

Worked all like a hot knife is slicing butter! Thank you so much, I learned a looot today. :) Realized the same thing in png myself at least. To further continue learning myself, next step will be trying to do rounded corners except one for the finders without help.^^