1. Lecture 3: G.O. architecture + Polymorphism

2. Goal GameObject (GO) class Similar to Unity
Contains transformation info
As a matrix
T * S * R (right-handed)
“Snap-in” Components
Many of which are Ogre-wrappers
LightComponent
EntityComponent
ParticleEmitterComponent
BillboardComponent …
Broadcasting messages
Parent / Child relationship
Unity Hierarchy

3. First attempt
class GameObject { protected: ??? mTransformation; ??? mComponents; public: setPosition(???); … addMeshComponent(???); addCameraComponent(???); };

4. The Transformation part
Ogre SceneNode
Methods for creating
Getting via SceneManager.
Methods for setting position, scale, orientation
Methods for modifying position, scale, rotation
Parenting SceneNodes
Attaching Stuff
Role of MoveableObject class.
Detaching objects
Destroying the scene node

5. Tangent_1: C++ Inheritance
a.h
a.cpp
class A {
protected:
int mValue;
public:
A(int x);
~A();
void foo(); };
#include <a.h>
A::A(int x) : mX(x) {
cout << “A(“ << x << “)!\n”; }
// Same thing, but less efficient
//A::A(int x)
//{
// mX = x; // or this->mX = x;
//}
A::~A()
cout << “A(“ << mX << “)vv\n”;
void A::foo()
cout << “AAA” << endl;

6. Tangent_1: C++ Inheritance
b.h
b.cpp
class B : public A {
public:
B(int x);
~B();
void foo(); };
#include <b.h>
// We *must* do this – see why?
B::B(int x) : A(x) {
cout << “B(“ << mX << “)!\n”; }
B::~B()
cout << “B(“ << mX << “)vv\n”;
void A::foo()
cout << “BBB” << endl;

7. Tangent_2: C++ Polymorphism
Ability to assign address of derived class to base-class pointer
[Trace output of this snippet]
A* val1 = new A(15);
B* val2 = new B(16);
A* val3 = val2; // !!!
val1->foo();
val2->foo();
val3->foo(); // !!!
// Don’t forget these!
delete val1;
delete val2;
// delete val3; // !!!

8. Tangent_2: C++ Polymorphism
Why didn’t val3->foo() do what we thought?
Static linkage (static resolution)
We (here) want dynamic resolution
To get it…
class A {
protected:
int mValue;
public:
A(int x);
virtual ~A();
virtual void foo(); };

9. Tangent_2: C++ Polymorphism
Role of virtual function table (vfptr)
Reason for virtual destructor?
Can put virtual in derived class
When is it necessary?

10. Tangent_3: Pure virtual
Syntax:
virtual void func() = 0;
Similar to Java abstract method
When to use it.

11. back to GO I want a Component class
And multiple derived classes (eventually)
MeshComponent
SoundComponent
CameraComponent
LightComponent …
We need a place to store them
DD: Multiple components vs. one-only.
DD: How to store / access them (recommend map)
DD: Who creates them?

12. Discuss architecture …

13. Ogre Entity An instance of a mesh
Built-in functionality for (binary) .mesh
There are exporters for Blender / Maya / etc.
Code to load them
Code to attach them to SceneNodes

14. tangent_4: circular includes
[On board]