Class question

This is a discussion on Class question within the C++ Programming forums, part of the General Programming Boards category; Wouldnt the use of dynamic_cast remove some of the point of designing my primitive class as I have done? I ...

  1. #16
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    Wouldnt the use of dynamic_cast remove some of the point of designing my primitive class as I have done?

    I am steeling the idea of how to do this primitive/ scene class from a tutorial on how to write a raytracer, and in that tutorial they do it as I do, just without the erros.'

    Code:
    // -----------------------------------------------------------
    // Primitive class definition
    // -----------------------------------------------------------
    
    class Primitive
    {
    public:
    	enum
    	{
    		SPHERE = 1,
    		PLANE
    	};
    	Primitive() : m_Name( 0 ), m_Light( false ) {};
    	Material* GetMaterial() { return &m_Material; }
    	void SetMaterial( Material& a_Mat ) { m_Material = a_Mat; }
    	virtual int GetType() = 0;
    	virtual int Intersect( Ray& a_Ray, float& a_Dist ) = 0;
    	virtual vector3 GetNormal( vector3& a_Pos ) = 0;
    	virtual Color GetColor( vector3& ) { return m_Material.GetColor(); }
    	virtual void Light( bool a_Light ) { m_Light = a_Light; }
    	bool IsLight() { return m_Light; }
    	void SetName( char* a_Name );
    	char* GetName() { return m_Name; }
    protected:
    	Material m_Material;
    	char* m_Name;
    	bool m_Light;
    };
    
    // -----------------------------------------------------------
    // Sphere primitive class definition
    // -----------------------------------------------------------
    
    class Sphere : public Primitive
    {
    public:
    	int GetType() { return SPHERE; }
    	Sphere( vector3& a_Centre, float a_Radius ) : 
    		m_Centre( a_Centre ), m_SqRadius( a_Radius * a_Radius ), 
    		m_Radius( a_Radius ), m_RRadius( 1.0f / a_Radius ) {};
    	vector3& GetCentre() { return m_Centre; }
    	float GetSqRadius() { return m_SqRadius; }
    	int Intersect( Ray& a_Ray, float& a_Dist );
    	vector3 GetNormal( vector3& a_Pos ) { return (a_Pos - m_Centre) * m_RRadius; }
    private:
    	vector3 m_Centre;
    	float m_SqRadius, m_Radius, m_RRadius;
    };
    Code:
    m_Primitive = new Primitive*[100];
    	// ground plane
    	m_Primitive[0] = new PlanePrim( vector3( 0, 1, 0 ), 4.4f );
    	m_Primitive[0]->SetName( "plane" );
    	m_Primitive[0]->GetMaterial()->SetReflection( 0 );
    	m_Primitive[0]->GetMaterial()->SetDiffuse( 1.0f );
    	m_Primitive[0]->GetMaterial()->SetColor( Color( 0.4f, 0.3f, 0.3f ) );
    	
    	// big sphere
    	m_Primitive[1] = new Sphere( vector3( 1, -0.8f, 3 ), 2.5f );
    	m_Primitive[1]->SetName( "big sphere" );
    	m_Primitive[1]->GetMaterial()->SetReflection( 0.6f );
    	m_Primitive[1]->GetMaterial()->SetColor( Color( 0.7f, 0.7f, 0.7f ) );
    As you see, here all object can be treathed the same, which makes all much more easy.
    Also, with this code I can call primitve[0].intersection(), so that I dont have to think about what kind of object I am testing. So, what am I doint wrong as my code dont work, but this does?

    Thanks

  2. #17
    Cat without Hat CornedBee's Avatar
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    Code:
    m_Primitive[1] = new Sphere( vector3( 1, -0.8f, 3 ), 2.5f );
    This is the key difference: constructor arguments.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  3. #18
    C++ Witch laserlight's Avatar
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    As you see, here all object can be treathed the same, which makes all much more easy.
    I note that every time you subclass Primitive in that class design, you need to alter it.

    Wouldnt the use of dynamic_cast remove some of the point of designing my primitive class as I have done?
    As CornedBee mentioned, you should consider using an appropriate constructor first.
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  4. #19
    l2u
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    What is wrong with dynamic_cast?
    I often use boost::dynamic_pointer_cast for smart pointers.

  5. #20
    Cat without Hat CornedBee's Avatar
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    The use of dynamic_cast suggests that your class hierarchy design has somehow failed: perhaps your base class was not expressive enough, or a function is getting data from the wrong place.
    There are situations where dynamic_cast is necessary, but all literature agrees that if you use dynamic_cast "often", there's a problem.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  6. #21
    l2u
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    boost::dynamic_pointer_cast, dynamic_cast - is that the same/similar, regarding what you previously said about dynamic_cast?

  7. #22
    Cat without Hat CornedBee's Avatar
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    Yes. The difference is that dynamic_pointer_cast works with pointers and smart pointers alike. (Not sure which smart pointers beyond shared_ptr are supported.)
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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