Question

I am writing an GL effect system in my application so i have a superclass called

cEffect – which handles loading/parsing configuration file for each effect

and other inherited classess

cFX<name> – for every effect i add ( blur, bloom, chaos,… ).

The code is simplified here but looks like this:

Class cEffect
{
    public:
     bool ParseString(...);

    private:
     int m_nStartFrame;
     int m_nEndFrame;
     float m_fSpeed;
};


// Blur effect
Class cFXBlur : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Bloom effect
Class cFXBloom : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Scene drawing effect
Class cFXScene : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Clear the depth/color buffer
Class cFXClearBuffers : public cEffect
{
  public
   bool RenderFrame(...);
}

Now, the demo engine handles a

std::vector<cEffect *> m_pvEffects;

Vector that has a list of effects added.
And when an effect is added to the current time (let’s say i add a blur)
i add it like:

// Blur to be added 

cEffect *newEffect = new cFXBlur;
newEffect->SetStartTime(x);
newEffect->SetEndTime(y);
newEffect->SetPower(13.0f);
newEffect->SetTexture(...);

// Now add the effect to the effects list.
m_pvEffects.push_back(newEffect);

Now, when i render i iterate through m_pvEffects list – but also i would like to call
an RenderFrame method ( which is public in every CFX<name> effect).

(*it)->RenderFrame(...) 

But compiler says:

error C2039: ‘RenderFrame’ : is not a member of ‘CEffect’

I kinda understand why it happens but can’t really think of a way how can i fix this,
can you guys help me out please – it seems like i lost the plot …

Thanks for any suggestion, what can i do to add CFX to a cEffect vector and later
use -> RenderFrame method?

Answer 1

You should change your class cEffect to:

Class cEffect
{
    public:
     bool ParseString(...);
     virtual bool RenderFrame(...) = 0;

    private:
     int m_nStartFrame;
     int m_nEndFrame;
     float m_fSpeed;
};

You need the keyword virtual, if you want to redefine a method in a subclass. The = 0 makes the class cEffect abstract (i.e. you cannot create an object directly of the type cEffect), therefore subclasses must implement the method RenderFrame(...)