我最喜欢的游戏引擎结构是使用消息传递进行几乎所有部分之间的通信的接口和对象<->组件模型。
您具有用于主机部件的多个接口，例如场景管理器，资源加载器，音频，渲染器，物理等。
我让场景管理器负责3D场景/世界中的所有对象。
对象是一个非常原子的类，仅包含场景中几乎所有事物所共有的一些内容，在我的引擎中，对象类仅包含位置，旋转，组件列表和唯一ID。每个对象的ID是由一个静态int生成的，因此，没有两个对象都具有相同的ID，这使您可以通过其ID向对象发送消息，而不必具有指向该对象的指针。
对象上的组件列表使对象成为主要属性。例如，对于3D世界中可以看到的东西，可以为对象提供一个渲染组件，其中包含有关渲染网格物体的信息。如果您希望某个对象具有物理特性，则可以给它一个物理特性。如果要让某些东西充当照相机，请为其提供照相机组件。组件列表可以继续。
接口，对象和组件之间的通信是关键。在我的引擎中，我有一个通用的消息类，该类仅包含唯一的ID和消息类型ID。唯一ID是您希望消息转到的对象的ID，消息类型ID由接收消息的对象使用，因此它知道消息的类型。
对象可以根据需要处理消息，并且可以将消息传递给它们的每个组件，并且组件通常会对消息起重要作用。例如，如果要更改对象的位置并向其发送SetPosition消息，则对象在收到消息时可能会更新其位置变量，但是渲染组件可能需要消息以更新渲染网格的位置，并且物理组件可能需要消息来更新物理体的位置。
这是场景管理器，对象和组件以及消息流的非常简单的布局，我花了大约一个小时才用C ++编写。运行时，它将在对象上设置位置，然后消息通过渲染组件，然后从对象中检索位置。请享用！
另外，我为可能精通这些语言而不是C ++的任何人编写了以下代码的C＃版本和Scala版本。
#include <iostream>
#include <stdio.h>
#include <list>
#include <map>
using namespace std;
struct Vector3
{
public:
Vector3() : x(0.0f), y(0.0f), z(0.0f)
{}
float x, y, z;
};
enum eMessageType
{
SetPosition,
GetPosition,
};
class BaseMessage
{
protected: // Abstract class, constructor is protected
BaseMessage(int destinationObjectID, eMessageType messageTypeID)
: m_destObjectID(destinationObjectID)
, m_messageTypeID(messageTypeID)
{}
public: // Normally this isn't public, just doing it to keep code small
int m_destObjectID;
eMessageType m_messageTypeID;
};
class PositionMessage : public BaseMessage
{
protected: // Abstract class, constructor is protected
PositionMessage(int destinationObjectID, eMessageType messageTypeID,
float X = 0.0f, float Y = 0.0f, float Z = 0.0f)
: BaseMessage(destinationObjectID, messageTypeID)
, x(X)
, y(Y)
, z(Z)
{
}
public:
float x, y, z;
};
class MsgSetPosition : public PositionMessage
{
public:
MsgSetPosition(int destinationObjectID, float X, float Y, float Z)
: PositionMessage(destinationObjectID, SetPosition, X, Y, Z)
{}
};
class MsgGetPosition : public PositionMessage
{
public:
MsgGetPosition(int destinationObjectID)
: PositionMessage(destinationObjectID, GetPosition)
{}
};
class BaseComponent
{
public:
virtual bool SendMessage(BaseMessage* msg) { return false; }
};
class RenderComponent : public BaseComponent
{
public:
/*override*/ bool SendMessage(BaseMessage* msg)
{
// Object has a switch for any messages it cares about
switch(msg->m_messageTypeID)
{
case SetPosition:
{
// Update render mesh position/translation
cout << "RenderComponent handling SetPosition\n";
}
break;
default:
return BaseComponent::SendMessage(msg);
}
return true;
}
};
class Object
{
public:
Object(int uniqueID)
: m_UniqueID(uniqueID)
{
}
int GetObjectID() const { return m_UniqueID; }
void AddComponent(BaseComponent* comp)
{
m_Components.push_back(comp);
}
bool SendMessage(BaseMessage* msg)
{
bool messageHandled = false;
// Object has a switch for any messages it cares about
switch(msg->m_messageTypeID)
{
case SetPosition:
{
MsgSetPosition* msgSetPos = static_cast<MsgSetPosition*>(msg);
m_Position.x = msgSetPos->x;
m_Position.y = msgSetPos->y;
m_Position.z = msgSetPos->z;
messageHandled = true;
cout << "Object handled SetPosition\n";
}
break;
case GetPosition:
{
MsgGetPosition* msgSetPos = static_cast<MsgGetPosition*>(msg);
msgSetPos->x = m_Position.x;
msgSetPos->y = m_Position.y;
msgSetPos->z = m_Position.z;
messageHandled = true;
cout << "Object handling GetPosition\n";
}
break;
default:
return PassMessageToComponents(msg);
}
// If the object didn't handle the message but the component
// did, we return true to signify it was handled by something.
messageHandled |= PassMessageToComponents(msg);
return messageHandled;
}
private: // Methods
bool PassMessageToComponents(BaseMessage* msg)
{
bool messageHandled = false;
auto compIt = m_Components.begin();
for ( compIt; compIt != m_Components.end(); ++compIt )
{
messageHandled |= (*compIt)->SendMessage(msg);
}
return messageHandled;
}
private: // Members
int m_UniqueID;
std::list<BaseComponent*> m_Components;
Vector3 m_Position;
};
class SceneManager
{
public:
// Returns true if the object or any components handled the message
bool SendMessage(BaseMessage* msg)
{
// We look for the object in the scene by its ID
std::map<int, Object*>::iterator objIt = m_Objects.find(msg->m_destObjectID);
if ( objIt != m_Objects.end() )
{
// Object was found, so send it the message
return objIt->second->SendMessage(msg);
}
// Object with the specified ID wasn't found
return false;
}
Object* CreateObject()
{
Object* newObj = new Object(nextObjectID++);
m_Objects[newObj->GetObjectID()] = newObj;
return newObj;
}
private:
std::map<int, Object*> m_Objects;
static int nextObjectID;
};
// Initialize our static unique objectID generator
int SceneManager::nextObjectID = 0;
int main()
{
// Create a scene manager
SceneManager sceneMgr;
// Have scene manager create an object for us, which
// automatically puts the object into the scene as well
Object* myObj = sceneMgr.CreateObject();
// Create a render component
RenderComponent* renderComp = new RenderComponent();
// Attach render component to the object we made
myObj->AddComponent(renderComp);
// Set 'myObj' position to (1, 2, 3)
MsgSetPosition msgSetPos(myObj->GetObjectID(), 1.0f, 2.0f, 3.0f);
sceneMgr.SendMessage(&msgSetPos);
cout << "Position set to (1, 2, 3) on object with ID: " << myObj->GetObjectID() << '\n';
cout << "Retreiving position from object with ID: " << myObj->GetObjectID() << '\n';
// Get 'myObj' position to verify it was set properly
MsgGetPosition msgGetPos(myObj->GetObjectID());
sceneMgr.SendMessage(&msgGetPos);
cout << "X: " << msgGetPos.x << '\n';
cout << "Y: " << msgGetPos.y << '\n';
cout << "Z: " << msgGetPos.z << '\n';
}