原文链接：TetroGL: An OpenGL Game Tutorial in C++ for Win32 Platforms - Part 1
这个系列专注于使用C++和OpenGL在windows平台上开发2D游戏，项目目标是在系列结束后能开发出一个类似俄罗斯方块的游戏。本系列分为3篇文章：
第一部分：涉及win32消息循环，窗口创建和OpenGL的搭建，并且你将会学习如何绘制一些简单的图形。
第二部分：涉及资源处理和简单动画的显示
第三部分：将前面的内容包含进来，并且讨论游戏逻辑。
项目设置
作者做了两项设置：
1） LinkeràInput中，在” Addition Dependencies”中加入”opengl32.lib”，
2） 禁掉UNICODE，“c/c++”à” Preprocessor”,在Preprocessor Definitions中将"Inherit from parent or project defaults"不选中。
消息循环
Windows系统为每个应用程序创建一个消息队列，当指定应用程序的窗口上发生一个事件时，系统会把消息推入到这个队列中。你的应用程序应当检索并处理这些消息。这就是所谓的“消息循环“，是win32应用程序的核心。
一个典型的消息循环如下：
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MSG Message;
Message.message = (~WM_QUIT);
// Loop until a WM_QUIT message is received
while (Message.message != WM_QUIT)
{
if (PeekMessage(&Message, NULL, 0, 0, PM_REMOVE))
{
// If a message was waiting in the message queue, process it
TranslateMessage(&Message);
DispatchMessage(&Message);
}
else
{//空闲时
// Do processing stuff here
}
}
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TranslateMessage函数的目的是为了将虚键消息（WM_KEYDOWN和WM_KEYUP）为字符消息（WM_CHAR）.最后DispatchMessage会将消息定向到正确的窗口处理程序。
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// The application class, which simply wraps the message queue and process
// the command line.
class CApplication
{
public:
CApplication(){}
CApplication(HINSTANCE hInstance);
~CApplication();
// Parses the command line to see if the application
// should be in fullscreen mode.
void ParseCmdLine(LPSTR lpCmdLine);
// Creates the main window and start the message loop.
void Run();
void SetHInst(HINSTANCE hInstance);
private:
HINSTANCE m_hInstance;
// Specifies if the application has to be started in fullscreen
// mode. This option is supplied through the command line
// ("-fullscreen" option).
bool m_bFullScreen;
};
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ParseCmdLine函数功能非常直观：仅仅简单地检查命令行中是否有参数"-fullscreen"，如果有，则设置m_bFullScreen为true,表示窗口模式为全屏模式。
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void CApplication::Run()
{
// Create the main window first
CMainWindow mainWindow(800,600,m_bFullScreen);
MSG Message;
Message.message = ~WM_QUIT;
DWORD dwNextDeadLine = GetTickCount() + 30;
DWORD dwSleep = 30;
bool bUpdate = false;
// Loop until a WM_QUIT message is received
while (Message.message != WM_QUIT)
{
// Wait until a message comes in or until the timeout expires. The
// timeout is recalculated so that this function will return at
// least every 30 msec.
DWORD dwResult = MsgWaitForMultipleObjectsEx(0,NULL,dwSleep,QS_ALLEVENTS,0);
if (dwResult != WAIT_TIMEOUT)
{
// If the function returned with no timeout, it means that a
// message has been received, so process it.
if (PeekMessage(&Message, NULL, 0, 0, PM_REMOVE))
{
// If a message was waiting in the message queue, process it
TranslateMessage(&Message);
DispatchMessage(&Message);
}
// If the current time is close (or past) to the
// deadline, the application should be processed.
if (GetTickCount() >= dwNextDeadLine-1)
bUpdate = true;
}
else
// On a timeout, the application should be processed.
bUpdate = true;
// Check if the application should be processed
if (bUpdate)
{
DWORD dwCurrentTime = GetTickCount();
// Update the main window
mainWindow.Update(dwCurrentTime);
// Draw the main window
mainWindow.Draw();
dwNextDeadLine = dwNextDeadLine + 30;
dwSleep = 30;
}
else
dwSleep = dwNextDeadLine - GetCurrentTime();
}
}
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函数第一行创建主窗口。和常见的消息循环不同，由于在2D游戏中并不需要很快地刷新屏幕，以固定地速率（这里是30毫秒）刷新，对于绘制动画和其他处理已经足够了。
作者在这里使用的技巧就是出于这个目的，他使用了MsgWaitForMultipleObjectsEx函数来等待任何事件的发生，再判断是30毫秒的时限已到，还是有事件要处理，若是后者，则先处理事件，在处理完后，若此时也已经接近30毫秒的时限的话，就重绘界面，若是超时发生了，则说明30毫秒时限已到，需要去刷新界面了。若这两种情况都没有的话，这个函数不会消耗 CPU周期，线程只是被挂起，不参与调度。
主窗口
创建窗口
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CMainWindow::CMainWindow(int iWidth, int iHeight, bool bFullScreen)
: m_hWindow(NULL), m_hDeviceContext(NULL), m_hGLContext(NULL),
m_bFullScreen(bFullScreen)
{
RegisterWindowClass();
RECT WindowRect;
WindowRect.top = WindowRect.left = 0;
WindowRect.right = iWidth;
WindowRect.bottom = iHeight;
// Window Extended Style
DWORD dwExStyle = 0;
// Windows Style
DWORD dwStyle = 0;
if (m_bFullScreen)
{
DEVMODE dmScreenSettings;
memset(&dmScreenSettings,0,sizeof(dmScreenSettings));
dmScreenSettings.dmSize = sizeof(dmScreenSettings);
dmScreenSettings.dmPelsWidth = iWidth;
dmScreenSettings.dmPelsHeight = iHeight;
dmScreenSettings.dmBitsPerPel = 32;
dmScreenSettings.dmFields = DM_PELSWIDTH | DM_PELSHEIGHT | DM_BITSPERPEL;
// Change the display settings to fullscreen. On error, throw
// an exception.
if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)
!= DISP_CHANGE_SUCCESSFUL)
{
throw CException("Unable to swith to fullscreen mode");
}
dwExStyle = WS_EX_APPWINDOW;
dwStyle = WS_POPUP;
// In fullscreen mode, we hide the cursor.
ShowCursor(FALSE);
}
else
{
dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;
dwStyle = WS_OVERLAPPEDWINDOW;
}
// Adjust the window to the true requested size
AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle);
// Now create the main window
m_hWindow = CreateWindowEx(dwExStyle,TEXT(WINDOW_CLASSNAME),
TEXT("Tutorial1"),
WS_CLIPSIBLINGS | WS_CLIPCHILDREN | dwStyle,
0, 0, WindowRect.right-WindowRect.left,
WindowRect.bottom-WindowRect.top,
NULL, NULL,
GetModuleHandle(NULL),
this);
if (m_hWindow==NULL)
throw CException("Cannot create the main window");
CreateContext();
InitGL();
ShowWindow(m_hWindow,SW_SHOW);
// Call OnSize manually because in fullscreen mode it will be
// called only when the window is created (which is too early
// because OpenGL is not initialized yet).
OnSize(iWidth,iHeight);
}
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在构造函数中，检查完是否需要进入全屏模式后，通过调用ChangeDisplaySettings来切换到全屏模式，然后调用AdjustWindowRectEx来调整矩形的大小，但这个函数在全屏模式下没什么作用，最后CreateContext和InitGL对OpenGL进行初始化。
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LRESULT CMainWindow::OnEvent(HWND Handle, UINT Message, WPARAM wParam, LPARAM lParam)
{
if (Message == WM_CREATE)
{
// Get the creation parameters.
CREATESTRUCT* pCreateStruct = reinterpret_cast<CREATESTRUCT*>(lParam);
// Set as the "user data" parameter of the window
SetWindowLongPtr(Handle, GWLP_USERDATA,
reinterpret_cast<long>(pCreateStruct->lpCreateParams));
}
// Get the CMainWindow instance corresponding to the window handle
CMainWindow* pWindow = reinterpret_cast<CMainWindow*>
(GetWindowLongPtr(Handle, GWLP_USERDATA));
if (pWindow)
pWindow->ProcessEvent(Message,wParam,lParam);
return DefWindowProc(Handle, Message, wParam, lParam);
}
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由于OnEvent函数是静态的，因此就没法访问非静态成员，为了解决这个问题，在调用CreateWindowEx创建窗口时最后一个参数传的是this指针。传给窗口处理过程的第一个消息是WM_CREATE，当接收到这个消息时，wParam参数中包含一个CREATESTRUCT指针，它里面包含了额外的数据，在这里是指向CMainWindow的指针。但遗憾的是，不是每个消息都有这个结构，所以要保存起来供后面使用。因此调用SetWindowLongPtr,它的目的是为一个特定的窗口保存一些用户数据(GWLP_USERDATA)。在这里，作者保存了到类实例的指针。当接收到其他消息时，我们只是简单地通过GetWindowLongPtr来取回这个指针，然后访问非静态函数ProcessEvent，而这个函数负责具体的消息处理。
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void CMainWindow::ProcessEvent(UINT Message, WPARAM wParam, LPARAM lParam)
{
switch (Message)
{
// Quit when we close the main window
case WM_CLOSE :
PostQuitMessage(0);
break;
case WM_SIZE:
OnSize(LOWORD(lParam),HIWORD(lParam));
break;
case WM_KEYDOWN :
break;
case WM_KEYUP :
break;
}
}
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异常处理
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class CException : public std::exception
{
public:
const char* what() const { return m_strMessage.c_str(); }
CException(const std::string& strMessage="") : m_strMessage(strMessage) { }
virtual ~CException() { }
std::string m_strMessage;
};
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使用的实例：
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CApplication theApp;
int WINAPI WinMain(HINSTANCE Instance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, INT)
{
try
{
// Create the application class,
// parse the command line and
// start the app.
theApp.SetHInst(Instance);
theApp.ParseCmdLine(lpCmdLine);
theApp.Run();
}
catch(CException& e)
{
MessageBox(NULL,e.what(),"Error",MB_OK|MB_ICONEXCLAMATION);
}
return 0;
}
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初始化OpenGL
CreateContext用来初始化绘制上下文，使得OpenGL基本元素可以在窗口上绘制：
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void CMainWindow::CreateContext()
{
// Describes the pixel format of the drawing surface
PIXELFORMATDESCRIPTOR pfd;
memset(&pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
pfd.nVersion = 1; // Version Number
pfd.dwFlags = PFD_DRAW_TO_WINDOW | // Draws to a window
PFD_SUPPORT_OPENGL | // The format must support OpenGL
PFD_DOUBLEBUFFER; // Support for double buffering
pfd.iPixelType = PFD_TYPE_RGBA; // Uses an RGBA pixel format
pfd.cColorBits = 32; // 32 bits colors
if (!(m_hDeviceContext=GetDC(m_hWindow)))
throw CException("Unable to create rendering context");
int PixelFormat;
// Do Windows find a matching pixel format ?
if (!(PixelFormat=ChoosePixelFormat(m_hDeviceContext,&pfd)))
throw CException("Unable to create rendering context");
// Set the new pixel format
if(!SetPixelFormat(m_hDeviceContext,PixelFormat,&pfd))
throw CException("Unable to create rendering context");
// Create the OpenGL rendering context
if (!(m_hGLContext=wglCreateContext(m_hDeviceContext)))
throw CException("Unable to create rendering context");
// Activate the rendering context
if(!wglMakeCurrent(m_hDeviceContext,m_hGLContext))
throw CException("Unable to create rendering context");
}
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函数的第一部分填充PIXELFORMATDESCRIPTOR结构体：缓冲区用来绘制到窗口上，支持OpenGL，使用双缓存（为了避免闪烁）。然后调用ChoosePixelFormat来检查像素格式是否支持，这个函数返回一个像素格式索引（若没有找到匹配的，则返回0）。一旦存在这样的像素格式索引，则通过SetPixelFormat来设置新像素格式。然后调用wglCreateContext创建OpenGL绘制上下文，最后，调用wglMakeCurrent,这指明线程接下来的OpenGL调用会绘制在这个设备上下文上。
InitGL函数很简单：
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void CMainWindow::InitGL()
{
// Enable 2D texturing
glEnable(GL_TEXTURE_2D);
// Choose a smooth shading model
glShadeModel(GL_SMOOTH);
// Set the clear color to black
glClearColor(0.0, 0.0, 0.0, 0.0);
}
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再看OnSize函数
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void CMainWindow::OnSize(GLsizei width, GLsizei height)
{
// Sets the size of the OpenGL viewport
glViewport(0,0,width,height);
// Select the projection stack and apply
// an orthographic projection
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0,width,height,0.0,-1.0,1.0);
glMatrixMode(GL_MODELVIEW);
}
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正交投影
透视投影
绘制简单图形
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void CMainWindow::Draw()
{
// Clear the buffer
glClear(GL_COLOR_BUFFER_BIT);
// Here goes the drawing code
glBegin(GL_QUADS);
glColor3f(1.0,0.0,0.0); glVertex3i(50,200,0);
glColor3f(0.0,1.0,0.0); glVertex3i(250,200,0);
glColor3f(0.0,0.0,1.0); glVertex3i(250,350,0);
glColor3f(1.0,1.0,1.0); glVertex3i(50,350,0);
glEnd();
glBegin(GL_TRIANGLES);
glColor3f(1.0,0.0,0.0); glVertex3i(400,350,0);
glColor3f(0.0,1.0,0.0); glVertex3i(500,200,0);
glColor3f(0.0,0.0,1.0); glVertex3i(600,350,0);
glEnd();
SwapBuffers(m_hDeviceContext);
}
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本文转自Phinecos(洞庭散人)博客园博客，原文链接：http://www.cnblogs.com/phinecos/archive/2008/06/26/1230692.html，如需转载请自行联系原作者
