GLUT的简洁OO封装

毕业设计用到了OpenGL，由于不会用MFC和Win32API做窗口程序；自然选用了GLUT。GLUT很好用，就是每次写一堆Init，注册callback，觉得有点恶心，于是对他做了简单的OO封装。记录在此，如有同学有兴趣可以下载。

GLUT应用程序

直接使用GLUT的程序是这样的：

#include <GL/glut.h>
#include <stdio.h>

void display()
{
// OpenGL commands
}

// 一般按键（所有可打印字符，ESC也在内）
void keyboardHander(unsigned char ch, int x, int y)
{
	printf("key %d(%c) x: %d, y: %d\n", ch, ch, x, y);
	fflush(stdout);
}

// 特殊按键
void specialKeyHandler(int key, int x, int y)
{
	printf("special key");

	switch(key) {
	case GLUT_KEY_UP:
		printf("%d(%s) ", key, "GLUT_KEY_UP");
		break;
	case GLUT_KEY_DOWN:
		printf("%d(%s) ", key, "GLUT_KEY_DOWN");
		break;
	case GLUT_KEY_LEFT:
		printf("%d(%s) ", key, "GLUT_KEY_LEFT");
		break;
	case GLUT_KEY_RIGHT:
		printf("%d(%s) ", key, "GLUT_KEY_RIGHT");
		break;
	default:
		printf("%d(%s) ", key, "Other Special keys");
	}
	printf("x: %d, y: %d\n", x, y);
	fflush(stdout);
}

// 鼠标按键
void mouseHandler(int button, int state, int x, int y)
{
	printf("mouse pos: (%3d, %3d) button: %s(%d), state: %s(%d)\n", x, y,
				GLUT_LEFT_BUTTON == button ? "GLUT_LEFT_BUTTON"
				: GLUT_RIGHT_BUTTON == button ? "GLUT_RIGHT_BUTTON"
				: GLUT_MIDDLE_BUTTON == button ? "GLUT_MIDDLE_BUTTON"
				: "UNKOW"
			, button,
				GLUT_UP == state ? "GLUT_UP"
				: GLUT_DOWN == state ? "GLUT_DOWN"
				: "UNKNOW"
			, state
			);
	fflush(stdout);
}

// 鼠标拖动
void motionHandler(int x, int y)
{
	printf("motion to %d, %d\n", x, y);
	fflush(stdout);
}

// 鼠标移动
void passiveMotionHandler(int x, int y)
{
	printf("passive motion to %d, %d\n", x, y);
	fflush(stdout);
}

void testTimer(int i)
{
	printf("Alarm %d\n", i);
	fflush(stdout);
	if( i < 5 )
		glutTimerFunc(1000, testTimer, i+1);
}

int main(int argc, char *argv[])
{
	glutInit(&argc, argv);

	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 300);
	glutInitWindowPosition(100, 100);
	glutCreateWindow("Getting started with OpenGL 4.3");

	glutDisplayFunc(display);

	glutKeyboardFunc(keyboardHander); // 键盘按键(一般)
	glutSpecialFunc(specialKeyHandler); // 特殊按键

	glutMouseFunc(mouseHandler); // 鼠标按键
	glutMotionFunc(motionHandler);  // 鼠标拖动
	glutPassiveMotionFunc(passiveMotionHandler); // 鼠标移动

	glutTimerFunc(1000, testTimer, 1); // 定时器

	glutMainLoop(); // start main loop.
	return 0;
}

用起来还算简单，就是每次都写一堆Init和callback注册...

于是，我想到是否能够将它封装为一个基类，然后每次继承一下（有点像Java，C#的窗体程序）。

也就是每个成员函数对应一种事件的响应，比如onKey, onMouse等等。我们希望我们的程序像下面这样：

int main(int argc, char **argv)
{
	GlutApp::initGlut(argc, argv);
	GlutApp* app = new DemoApp();

	app->setTitle("a demo app");
	app->setWindowsSize(800, 600);

	app->run();
	delete app;
	return 0;
}

Member function 如何作为Callback？

这里其实是两个问题。

第一个问题，member function的函数签名上有this指针，不能直接传给glut*Func作为callback，怎么办？

member function不行，很自然的想到static function；因为static function的函数签名上没有this指针。

第二个问题，static function如何能够调用member function，且与之关联的对象（this指针）能够在运行时期（或者用户程序）决定？

其一，static function调用member function自然要用到 static member。

其二，可让member function修改这个static member。

GlutApp

有了上面的分析，GlutApp类就可以轻易的写出来了：

GlutApp.h

#ifndef GLUT_APP_H
#define GLUT_APP_H

class GlutApp
{
public:
	typedef void (*MenuFuncPtr)(void);

	struct MenuEntry
	{
		int id;
		const char* str;
		MenuFuncPtr fun;
	};

	// 当前 App 实例指针,指向子类实例
	static GlutApp* s_pCurrentApp;

	// 右键菜单 项数最大值
	static const int MAX_MENU = 32;

	// ctor
	GlutApp();

	// getter and setters:
	static void initGlut(int argc, char** argv) { s_argc = argc; s_argv = argv; }

	void setDisplayMode(unsigned int mode) { m_displayMode = mode; }

	void setWindowsSize(int w, int h) { m_winWidth = w; m_winHeight = h; }

	int getWindowWidth() { return m_winWidth; }

	int getWindowHeight() { return m_winHeight; }

	void setWindowsPos(int x, int y) { m_winPosX = x; m_winPosY = y; }

	void setTitle(char *title) { m_title = title; }

	void run();

	void addRightMenu(const char *str, MenuFuncPtr fun);

	// 初始化
	virtual void onInit(){}

	//////////////////////////////////////////////////////////////////////////
	// GLUT delegate callbacks:

	// 空闲函数
	virtual void onIdle(){}

	// 图形显示（OpenGL绘图指令）
	virtual void onDisplay() = 0; // 子类必须重写；不能实例化该类

	// 窗口大小改变
	virtual void onResize(int w, int h){}

	//////////////////////////////////////////////////////////////////////////
	// 键盘事件响应 方法:

	// 一般按键（可打印字符，ESC）
	virtual void onKey(unsigned char key, int x, int y){}

	// 一般按键 按下
	virtual void onKeyDown(unsigned char key, int x, int y) {}

	// 特殊按键（除一般按键外按键）
	virtual void onSpecialKey(int key, int x, int y){}

	// 特殊按键按下
	virtual void onSpecialKeyDown(int key, int x, int y){}

	//////////////////////////////////////////////////////////////////////////
	// 鼠标事件响应 方法:

	// 鼠标按键
	//! @param button: The button parameter is one of GLUT LEFT BUTTON, GLUT MIDDLE BUTTON, or GLUT RIGHT BUTTON.
	//! @param state: The state parameter is either GLUT UP or GLUT DOWN indicating
	//                 whether the callback was due to a release or press respectively.
	virtual void onMousePress(int button, int state, int x, int y){}

	// 鼠标移动
	virtual void onMouseMove(int x, int y){}

	// 鼠标拖动
	virtual void onMousePressMove(int x,int y){}

	//////////////////////////////////////////////////////////////////////////
	// 定时器相关 方法：
	virtual void onTimer() {}

	void setTimer(int delay, int period = 0);

protected:
	void registerMenus();

	// actual GLUT callback functions:
	static void KeyboardCallback(unsigned char key, int x, int y);

	static void KeyboardUpCallback(unsigned char key, int x, int y);

	static void SpecialKeyboardCallback(int key, int x, int y);

	static void SpecialKeyboardUpCallback(int key, int x, int y);

	static void ReshapeCallback(int w, int h);

	static void IdleCallback();

	static void MouseFuncCallback(int button, int state, int x, int y);

	static void	MotionFuncCallback(int x,int y);

	static void MousePassiveCallback(int x, int y);

	static void DisplayCallback();

	static void MenuCallback(int menuId);

	static void TimerCallback(int period);
private:
	unsigned int m_displayMode;

	// for glutInit
	static int s_argc;
	static char** s_argv;

	char *m_title;

	// for glutSetWindowSize
	int m_winWidth;
	int m_winHeight;

	// for windows position
	int m_winPosX;
	int m_winPosY;

	// for menus:
	int       m_menuCount;
	MenuEntry m_menuEntry[MAX_MENU];

	// for timer:
	int m_delay;
	int m_period;
};

#endif // GLUT_APP_H

GlutApp.cpp

#include <gl/glut.h>
#include <assert.h>
#include <stdio.h>

#include "GlutApp.h"

int GlutApp::s_argc = 0;

char** GlutApp::s_argv = 0;

GlutApp* GlutApp::s_pCurrentApp = 0;

int g_iLastWindow = 0;

void GlutApp::run()
{
	GlutApp* lastApp = GlutApp::s_pCurrentApp;
	GlutApp::s_pCurrentApp = this;

	GlutApp* app = GlutApp::s_pCurrentApp;
	assert(app);

	int screenW = glutGet(GLUT_SCREEN_WIDTH);
	int screenH = glutGet(GLUT_SCREEN_HEIGHT);

	if (!app->m_winWidth)
	{
		app->m_winWidth = screenW / 2;
		app->m_winHeight = screenH / 2;
	}

	if (!app->m_winPosX)
	{
		app->m_winPosX = (screenW - app->m_winWidth) / 2;
		app->m_winPosY = (screenH - app->m_winHeight) / 2;
	}

	if (!lastApp) // first time calling Glut::run().
	{
		// glutInit that should only be called exactly once in a GLUT program.
		glutInit(&this->s_argc, this->s_argv);

		glutInitDisplayMode(this->m_displayMode);
		glutInitWindowPosition(app->m_winPosX, app->m_winPosY);
		glutInitWindowSize(app->m_winWidth, app->m_winHeight);

		glutCreateWindow(app->m_title);
		g_iLastWindow = glutGetWindow();
		// printf("create window: %d\n", g_iLastWindow);
	}
	else
	{
		glutDestroyWindow(g_iLastWindow);

		glutInitDisplayMode(this->m_displayMode);
		glutInitWindowPosition(app->m_winPosX, app->m_winPosY);
		glutInitWindowSize(app->m_winWidth, app->m_winHeight);

		glutCreateWindow(app->m_title);
		g_iLastWindow = glutGetWindow();
		// printf("create window: %d\n", g_iLastWindow);
	}

	app->onInit();

	// register keyboard callbacks
	glutKeyboardFunc(GlutApp::KeyboardCallback);
	glutKeyboardUpFunc(GlutApp::KeyboardUpCallback);
	glutSpecialFunc(GlutApp::SpecialKeyboardCallback);
	glutSpecialUpFunc(GlutApp::SpecialKeyboardUpCallback);

	// register mouse callbacks
	glutMouseFunc(GlutApp::MouseFuncCallback);
	glutMotionFunc(GlutApp::MotionFuncCallback);
	glutPassiveMotionFunc(GlutApp::MousePassiveCallback);

	// register menus:
	registerMenus();

	// regitser windows resize callback
	glutReshapeFunc(GlutApp::ReshapeCallback);

	// register render callback
	glutDisplayFunc(GlutApp::DisplayCallback);

	// register timer callbacks:
	if (app->m_delay)
	{
		glutTimerFunc(app->m_delay, GlutApp::TimerCallback, app->m_period);
	}

	// register idle callback
	glutIdleFunc(GlutApp::IdleCallback);

	GlutApp::IdleCallback();

	glutMainLoop();
}

GlutApp::GlutApp()
{
	m_displayMode = GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL;
	m_menuCount = 0;
	m_delay = 0;
	m_period = 0;

	m_winPosX = 0;
	m_winPosY = 0;
	m_winWidth = 0;
	m_winHeight = 0;
}

void GlutApp::KeyboardCallback( unsigned char key, int x, int y )
{
	GlutApp::s_pCurrentApp->onKey(key,x,y);
}

void GlutApp::KeyboardUpCallback( unsigned char key, int x, int y )
{
	GlutApp::s_pCurrentApp->onKeyDown(key,x,y);
}

void GlutApp::SpecialKeyboardCallback( int key, int x, int y )
{
	GlutApp::s_pCurrentApp->onSpecialKey(key,x,y);
}

void GlutApp::SpecialKeyboardUpCallback( int key, int x, int y )
{
	GlutApp::s_pCurrentApp->onSpecialKeyDown(key,x,y);
}

void GlutApp::ReshapeCallback( int w, int h )
{
	GlutApp::s_pCurrentApp->setWindowsSize(w, h);
	GlutApp::s_pCurrentApp->onResize(w,h);
}

void GlutApp::IdleCallback()
{
	GlutApp::s_pCurrentApp->onIdle();
}

void GlutApp::MouseFuncCallback( int button, int state, int x, int y )
{
	GlutApp::s_pCurrentApp->onMousePress(button,state,x,y);
}

void GlutApp::MotionFuncCallback( int x,int y )
{
	GlutApp::s_pCurrentApp->onMousePressMove(x,y);
}

void GlutApp::MousePassiveCallback( int x, int y )
{
	GlutApp::s_pCurrentApp->onMouseMove(x, y);
}

void GlutApp::DisplayCallback( void )
{
	GlutApp::s_pCurrentApp->onDisplay();
}

void GlutApp::addRightMenu( const char *str, MenuFuncPtr fun )
{
	m_menuEntry[m_menuCount].id = m_menuCount;
	m_menuEntry[m_menuCount].str = str;
	m_menuEntry[m_menuCount].fun = fun;
	m_menuCount++;
}

void GlutApp::registerMenus()
{
	if (m_menuCount > 0)
	{
		glutCreateMenu(GlutApp::MenuCallback);
		for (int i=0; i<m_menuCount; ++i)
		{
			glutAddMenuEntry(m_menuEntry[i].str, m_menuEntry[i].id);
		}
		glutAttachMenu(GLUT_RIGHT_BUTTON);
	}
}

void GlutApp::MenuCallback( int menuId )
{
	for (int i=0; i<GlutApp::s_pCurrentApp->m_menuCount; ++i)
	{
		if (menuId == GlutApp::s_pCurrentApp->m_menuEntry[i].id)
		{
			GlutApp::s_pCurrentApp->m_menuEntry[i].fun();
		}
	}
}

void GlutApp::setTimer( int delay, int period )
{
	this->m_delay = delay;
	this->m_period = period;
}

void GlutApp::TimerCallback( int period )
{
	// printf("Timer Alarm!\n");
	GlutApp::s_pCurrentApp->onTimer();
	if (period)
	{
		glutTimerFunc(period, GlutApp::TimerCallback, period);
	}
}

一个Demo

“伟大的三角形”，如同Hello world在编程语言教程里一样有名：

#include <windows.h> // 这里使用的是 Windows SDK 实现的OpenGL，必须写在<gl/gl.h>之前
#include <gl/gl.h>
#include <gl/glut.h>
#include <stdio.h>

#include "GlutApp.h"

class TestApp : public GlutApp
{
	virtual void onSpecialKeyDown( int key, int x, int y )
	{
		printf("onKeyDown: %d(%c), <%d, %d>\n", key, key, x, y);
	}

	virtual void onSpecialKey( int key, int x, int y )
	{
		printf("onSpecialKey: %d(%c), <%d, %d>\n", key, key, x, y);
	}

	virtual void onKeyDown( unsigned char key, int x, int y )
	{
		printf("onKeyDown: %d(%c), <%d, %d>\n", key, key, x, y);
	}

	virtual void onKey( unsigned char key, int x, int y )
	{
		printf("onKey: %d(%c), <%d, %d>\n", key, key, x, y);
	}

	virtual void onMouseMove( int x, int y )
	{
		printf("onMouseMove: %d, %d\n", x, y);
	}

	virtual void onMousePress( int button, int state, int x, int y )
	{
		printf("onMousePress: %d, %d, %d, %d\n", button, state, x, y);
	}

	virtual void onMousePressMove( int x,int y )
	{
		printf("onMousePressMove: %d, %d\n", x, y);
	}

	virtual void onInit()
	{
		printf("OnInit\n");

		glClearColor(0.0, 0.0, 0.0, 0.0);
		glShadeModel(GL_FLAT);
	}

	virtual void onDisplay()
	{
		glClear(GL_COLOR_BUFFER_BIT);

		// glPolygonMode(GL_FRONT, GL_LINE);

		glBegin(GL_TRIANGLES);
			glColor3f(1, 0, 0);
			glVertex2f(-1, -1);
			glVertex2f(1,  -1);
			glVertex2f(0, 1);
		glEnd();

		glFlush();
		glutSwapBuffers();
	}

	virtual void onResize( int w, int h )
	{
		printf("resize window: %d, %d\n", w, h);
	}

	virtual void onIdle()
	{

	}
};

void menu1() { printf("menu1 selected!\n"); }

void menu2() { printf("menu2 selected!\n"); }

void fullScreen() { glutFullScreen(); }

void exitApp() { exit(0); }

int main(int argc, char **argv)
{
	TestApp test;

	test.initGlut(argc, argv);
	test.setTitle("AppTest");
	test.setWindowsSize(640, 480);
	test.setDisplayMode(GLUT_RGBA | GLUT_SINGLE);

	test.addRightMenu("menu1", menu1);
	test.addRightMenu("menu2", menu2);
	test.addRightMenu("full screen", fullScreen);
	test.addRightMenu("exit", exitApp);

	test.run();

	return 0;
}