Game Engine Architecture

127

class Circle : public Shape

{

public:

void SetCenter(const Vector3& c) { m_center=c; }

Vector3 GetCenter() const { return m_center; }

void SetRadius(float r) { m_radius = r; }

float GetRadius() const { return m_radius; }

virtual void Draw()

{

// code to draw a circle

}

private:

Vector3 m_center;

float m_radius;

};

class Triangle : public Shape

{

public:

void SetVertex(int i, const Vector3& v);

Vector3 GetVertex(int i) const { return m_vtx[i]; }

virtual void Draw()

{

// code to draw a triangle

}

virtual void SetId(int id)

{

Shape::SetId(id);

Figure 3.18. pShape2 points to an instance of class Triangle.

Shape::m_id

Triangle::m_vtx[0]

Triangle::m_vtx[1]

vtable pointer pointer to SetId()

pointer to Draw ()

+0x00

+0x04

+0x08

+0x14

pShape2

Instance of Triangle Triangle’s Virtual Table

Triangle ::Draw(){

// code to draw a Triangle

}

Triangle ::SetId(int id)

{ Shape ::SetId(id);

// do additional work // specific to Triangles

}

+0x20 Triangle::m_vtx[2]

3.2. Data, Code, and Memory in C/C++