一：概述：

每个操作系统都有自己的图形系统，三维引擎会抽象出一个窗口，然后通过继承的方式，子类分别封装不同平台下面的窗口，另外，三维图形API也支持将内容渲染到其他表面上，比如纹理中，所以三维引擎也会抽象出一个纹理，再通过继承的方式，由子类分别封装不同图形API的纹理。

窗口和纹理，都可以看成一个抽象的画布，接收三维引擎的结果渲染到这个画布上，总体来说，一个抽象的画布，代表抽象的窗口或纹理，不同平台和图形API下的窗口和纹理又子类实现。这是三维引擎封装窗口系统的一种方法。

二：OSG的设计：

1：继承关系：

osg::GraphicsContext(图形系统抽象)

   |-osg::GraphicsWindow（窗口及渲染环境抽象）

|-osg::GraphicsWindowFOX（）

|-osg::GraphicsWindowWX（WX窗口）

|-osg::GraphicsWindowQt（QT窗口）

|-osg::GraphicsWindowCarbon（MacOS窗口）

|-osg::GraphicsWindowCocoa（Mac OS X窗口）

|-osg::GraphicsWindowIOS（IOS窗口）

|-osg::GraphicsWindowWin32（Win32窗口）

|-osg::GraphicsWindowX11(X11窗口)

|-osg::PixelBufferCarbon(MacOS像素缓存)

|-osg::PixelBufferCocoa(Mac OS X像素缓存)

|-osg::PixelBufferWin32(W32像素缓存)

|-osg::PixelBufferX11(X11像素缓存)

3. 三：OGRE的设计：

1：继承关系：

OgreRenderTarget（抽象画布，接收引擎绘制结果）

|-OgreRenderWindow（抽象窗口）

|-OgreWin32Window

|-OgreGLXWindow

|-OgreAndroidWindow

|-OgreD3D9RenderWindow

|-OgreD3D11RenderWindow

|-OgreEAGL2Window

|-OgreOSXCocoaWindow

|-OgreOSXWindow

|-OgreSDLWindow

|-OgreNaClWindow

|-OgreRenderTexture

|-D3D11RenderTexture

|-D3D9RenderTexture

|-GLESRenderTexture

|-GLES2RenderTexture

四： 窗口封装例子：

#ifndef CANVAS_H
#define CANVAS_H
#include <iostream>
#include <string>

#define CALLBACK

#define ES_WINDOW_RGB           0
#define ES_WINDOW_ALPHA         1
#define ES_WINDOW_DEPTH         2
#define ES_WINDOW_STENCIL       4
#define ES_WINDOW_MULTISAMPLE   8

namespace TDEngine {
typedef void (CALLBACK *TDEngineKeyFunc)(unsigned char, int, int);
typedef void (CALLBACK *TDEngineMouseFunc)(int, int, int, int);
typedef void (CALLBACK *TDEngineDrawFunc)();

class Canvas {

private:
	virtual bool initDisplay(void) 
        {
		return false;
	}

	virtual bool initWindow(void) 
        {
		return false;
	}

	virtual bool initContext(void) 
        {
		return false;
	}

	virtual bool userInterrupt(void) 
        {
		return false;
	}

public:
	Canvas() 
        {
		_width = 0;
		_height = 0;
		_flags = 0;

		_keyFunc = 0;
		_mouseFunc = 0;
		_drawFunc = 0;

		_currFps = 0;
		_frames = 0;
		_totalTime = 0;

		_wndType = 0;
		_eglDisplay = 0;
		_eglContext = 0;
		_eglSurface = 0;
		_eglConfig = 0;

		_clientWidth = 0;
		_clientHeight = 0;
		_handler = NULL;
		disableRootEvents = 0;
	}
	virtual ~Canvas() 
        {

	}

	virtual bool createWindow(int winWidth, int winHeight, int winOptions,std::string winTitle = "") =0;
	virtual void mainLoop(void) {}

	virtual void registerKeyboardFunc(TDEngineKeyFunc keyFunc) {}
	virtual void registerMouseFunc(TDEngineMouseFunc mouseFunc) {}
	virtual void registerDrawFunc(TDEngineDrawFunc drawFunc) {}
	virtual void addEventListener(std::string name, ScreenActionHandler action,bool bubble) = 0;
	virtual void removeEventListener(std::string name,ScreenActionHandler action, bool bubble) = 0;
	virtual void removeEventALLListener() = 0;
	virtual void fireEvents(const std::string& name,EventOption& eventOption) = 0;
public:
	int _width;
	int _height;
	int _flags;
	std::string _title;

	TDEngineKeyFunc _keyFunc;
	TDEngineMouseFunc _mouseFunc;
	TDEngineDrawFunc _drawFunc;

	float _currFps;
	int _frames;
	float _totalTime;

	unsigned long _wndType;
	void* _eglDisplay;
	void* _eglContext;
	void* _eglSurface;
	void* _eglConfig;

	int _clientWidth;
	int _clientHeight;

	ScreenSpaceEventHandler* _handler;
	std::map<std::string, ScreenActionHandler> _callbackActionList;
	bool disableRootEvents;

};
}

#endif // CANVAS_H

#ifndef CANVASX11_H
#define CANVASX11_H

#include  <X11/Xlib.h>
#include  <X11/Xatom.h>
#include  <X11/Xutil.h>

#include "Canvas.h"

#include "ScreenSpaceEventHandler.h"

namespace Cesium {

class CanvasX11: public Canvas {

public:
	Window _win;

private:
	virtual bool initDisplay(void);

	virtual bool initWindow(void);

	virtual bool initContext(void);

	virtual bool userInterrupt(void);

public:

	CanvasX11();

	virtual ~CanvasX11();

	virtual bool createWindow(int winWidth, int winHeight, int winOptions,
			std::string winTitle = "");

	virtual void mainLoop(void);

	virtual void registerKeyboardFunc(CesiumKeyFunc keyFun);

	virtual void registerMouseFunc(CesiumMouseFunc mouseFunc);

	virtual void registerDrawFunc(CesiumDrawFunc drawFunc);

	virtual void fireEvents(const std::string& name, EventOption& eventOption);

	virtual void addEventListener(std::string name, ScreenActionHandler action,
			bool bubble);

	virtual void removeEventALLListener(){

	}
	void removeEventListener(std::string name, ScreenActionHandler callback,
			bool bubble);

	static void moveMouse(Canvas& canvas, MouseButtons button,
				const Cartesian2& startPosition, const Cartesian2& endPosition,
				bool shiftKey = false);

	Display* get_xDisplay();

private:

	Display* _xDisplay;

	Window _rootWin;

private:

	typedef ScreenActionHandler CallFunc;

	typedef std::vector<CallFunc> CallFuncList;

	typedef std::map<std::string, CallFuncList> CallBacks;

	CallBacks _callbacks;


	std::vector<CallFunc> _keydown;
	std::vector<CallFunc> _mousemove;
	std::vector<CallFunc> _mouseup;
	std::vector<CallFunc> _mousedown;
	std::vector<CallFunc> _dblclick;
	std::vector<CallFunc> _mousewheel;
	std::vector<CallFunc> _touchstart;
	std::vector<CallFunc> _touchmove;
	std::vector<CallFunc> _touchend;

	S32 _numRegistered;



	bool _disableRootEvents;

};
}

#endif // CANVASX11_H

三维引擎设计-图形窗口封装