Hi there, my scenario is this one. I currently have a class which represents a Renderer, that has as an atribute a RenderQueue, that is actually a sorted list of pointers to "RenderableObjects". It goes like this:

class cRenderableObject {

  protected:
  int zValue;
  tPoint aPosition;

  public:
  virtual void mDraw() = 0; // Abstract
  friend bool operator<(const cRenderableObject &obj1, const cRenderableObject &obj2) {
	  return (obj1.zValue > obj2.zValue); // Descending sorting, cause it''s a z-buffering }
};


class cSurfaceObject : public cRenderableObject {

  private:
  CL_Surface* aImage;

  public:
  cSurfaceObject(CL_Surface* objImage,int posX, int posY, int zVal);
  void mDraw() { aImage->draw(aPosition.x,aPosition.y); }
};


class cRenderer {

  private:
  static std::list aRenderQueue;

  public:
  static void mAddToQueue(cRenderableObject* objImage);
  static void mRenderQueue();
};
 

So, at certain point y perform a: aRenderQueue.sort(); But, it''s not sorting properly. I think it''s not using the overloaded <"less" operator at all. Maybe it''s because i hold up a list of pointers to cRenderableObject class, and not a list to just objects? Well in that case, how can i accomplish the sorting properly? still using the pointers?. I need this for implementing/simulating a zbuffer for a 2D Graphic Adventure, since ClanLib (the gamelib i''m using), doesn''t support zbuffering/ordering right now. So i''ll keep a list of pointers to the objects to be rendered, updated and sorted at all times, and thanks to polimorphism i can call the ->mDraw() method for every object despite what class they really are. Thanks. If you need better explanations, ask for one.

Thanks a lot, i read at the book i''m using (The complete Reference C++, Herbert Shildt), that a functor or something could be specified, but i really didn''t know what that was. I tried passing pointers to functions and didn''t work.

Thanks a lot, both, saved my day =).

I''m getting a message from VC++ Compiler, stating this:

ImplementUtopia.cpp
C:\utopia\source\classes\ImplementUtopia.cpp(642) : error C2664: ''void __thiscall std::list >::sort(struct std::greater)'' : cannot convert parameter
1 from ''class cLessThan'' to ''struct std::greater''
No constructor could take the source type, or constructor overload resolution was ambiguous

--------------------------------------------------

Yoshin, i''ve followed your instructions and also took a look at some examples here: http://www.pixelate.co.za/issues/6/6/articles/stl2/part2.html, so everything looks fine in terms of declarations, but the compiler is complaining. Here''s how i did it:

At the interface:
------------------

class cLessThan {

public:
bool operator()(cRenderableObject* obj1, cRenderableObject* obj2) { return obj1->zValue > obj2->zValue; }

};

At the implementation:
----------------------

void cRenderer::mAddToQueue(cRenderableObject* objImage) {

// Agrego el objeto al Queue
aRenderQueue.push_back(objImage);

// Hago un sorting de la lista
aRenderQueue.sort(cLessThan());

}

------------------------------------

Everything seems fine, doesn''t it? Any clues? Thanks again //

For some reason, the sorting predicate you pass to std::list must be a greater<T> type. Beats me as to why.

To get around that, use the generalized sort algorithm sort:



And I wonder why a list needs a greater predicate...

[edited by - Zipster on March 3, 2003 2:08:20 AM]

quote:Original post by Zipster
For some reason, the sorting predicate you pass to std::list must be a greater type. Beats me as to why.

To get around that, use the generalized sort algorithm

Thats dropping me lot of errors. I''m not sure, but i think i read somewhere that the general sort couldn''t be used with the std::list. Please, correct me if i''m wrong...

Damn, i''m using visual studio. Does anybody knows another workaround then? What about that Greater predicate? What should i pass to the list::sort then, if it doesn''t want yo receive a comp functor?