I'm implementing a simple drawing program using Java/Processing.
There are simple geometric elements like triangles, rectangles etc. which I want to rotate according to mouse movement. Each element registers itself within the constructor using pApplet.registerElement(this).

Everything fine so far, but I struggle to rotate each element.
At the moment the element gets drawn temporarily (as long as the mouse is dragged):


After releasing the mouse button the unrotated element is still in its old place.

The display method looks something like that:

1. displayRotation(float theta)
2.  {

3.      pApplet_.pushMatrix();
         pApplet_.translate(pApplet_.width/2,pApplet_.height/2);
         pApplet_.rotate(theta);
         displayDefault();
         pApplet_.translate(-pApplet_.width/2, -pApplet_.height/2);
         pApplet_.popMatrix();
   

4.  }

There was a  similar problem with the built-in scale() function, although the according code snippet worked fine within Processing IDE.  I circumvented this problem by recalculating the side length of the rect, which then got redrawn automatically.

I guess I have to implement the rotation manually too, but how does this work?

Any help would be greatly appreciated!