源代碼下載：OpenGL_ch2.rar 

WGL – Windows的 OpenGL擴(kuò)展層

The WGL extension consists of a set of functions (wglCreateContext, wglDeleteContext etc.) and structures (such as PIXELFORMATDESCRIPTOR, GLYPHMETRICSFLOAT) etc. Thus every OpenGL implementation has a platform-specific portion which has to be set up and used according to the particular platform.

設(shè)備上下文

The Windows Graphical Device Interface (GDI) is capable of drawing to screen, to memory, to printers or to any other device that provides a GDI interface layer and that can process GDI calls. GDI accomplishes this by a rendering handle to the currently selected device, which is called the device context, or DC.

繪制上下文

A rendering context is the OpenGL equivalent of the GDI DC. All OpenGL calls are rendered to the device through a RC. The rendering context maintains OpenGL state variables such as current background color, current color etc. just as the DC maintains GDI state variables such as current pen, current brush etc.

像素格式

Pixel formats are the translation layer between OpenGL calls and the rendering operation that Windows performs.

舉個(gè)例子，若像素格式只支持很少一部分顏色值，則OpenGL在用RGB值(128,120,135)繪制一個(gè)像素時(shí)，就可能使用轉(zhuǎn)換后的值(128,128,128)來(lái)繪制.

The pixel format selected essentially describes such things as how colors are displayed, depth of field resolution and what additional capabilities are supported by the rendering context created.

第一個(gè)基于MFC的OpenGL應(yīng)用程

開(kāi)發(fā)環(huán)境：VC6.0

1， 首先下載需要的GLUT頭文件,DLL和Lib文件，下載鏈接: glutdlls37beta.zip (149 kilobytes),解壓縮后把gltu.h放到"VC98/Include/GL"下，把glut.lib和glut32.lib放到"VC9/Lib" 下，glut32.dll和glut.dll放到你創(chuàng)建的應(yīng)用程序的運(yùn)行目錄下

2， 創(chuàng)建一個(gè)MFC SDI應(yīng)用程序，在項(xiàng)目屬性中加入所需要鏈接的庫(kù)文件

1， 在stdafx.h中加入下列語(yǔ)句：

2， 打開(kāi)ClassWizard,選擇CCY457OpenGLView類，為下述消息加入消息處理函數(shù)：WM_CREATE (for OnCreate), WM_DESTROY (for OnDestroy), WM_SIZE (for OnSize), WM_ERASEBACKGROUND (for OnEraseBkground).

3,在窗口創(chuàng)建之前我們必須設(shè)置窗口風(fēng)格包含WS_CLIPCHILDREN和 WS_CLIPSIBLINGS，從而避免OpenGL繪制到其他窗口中去。這些應(yīng)該放在PreCreateWindow()中。

BOOL CCY457OpenGLView::PreCreateWindow(CREATESTRUCT& cs)
{
    // TODO: Modify the Window class or styles here by modifying
    //  the CREATESTRUCT cs
    //An OpenGL Window must be created with the following flags
    cs.style |= WS_CLIPSIBLINGS | WS_CLIPCHILDREN;
    return CView::PreCreateWindow(cs);
}

4, 在CCY457OpenGLView.h中加入如下語(yǔ)句：

    HGLRC m_hRC;    //Rendering Context
    CDC* m_pDC;        //Device Context
    BOOL InitializeOpenGL();    //Initialize OpenGL
    BOOL SetupPixelFormat();    //Set up the Pixel Format
    void RenderScene();            //Render the Scene

5, 在OnCreate中我們將通過(guò)建立像素格式和繪制上下文來(lái)初始化OpenGL. 在InitializeOpenGL()中會(huì)創(chuàng)建一個(gè)設(shè)備上下文(DC)，為這個(gè)DC選擇一個(gè)像素格式，創(chuàng)建和這個(gè)DC相關(guān)的繪制上下文（RC）,然后選擇這個(gè)RC.這個(gè)函數(shù)會(huì)調(diào)用SetupPixelFormat()來(lái)建立像素格式。

int CCY457OpenGLView::OnCreate(LPCREATESTRUCT lpCreateStruct) 
{
    if (CView::OnCreate(lpCreateStruct) == -1)
        return -1;
    //Initialize OpenGL Here
    InitializeOpenGL();
    return 0;
}

BOOL CCY457OpenGLView::InitializeOpenGL()
{
    //Get a DC for the Client Area
    m_pDC = new CClientDC(this);
    //Failure to Get DC
    if(m_pDC == NULL)
    {
        MessageBox("Error Obtaining DC");
        return FALSE;
    }
    //Failure to set the pixel format
    if(!SetupPixelFormat())
    {
        return FALSE;
    }
    //Create Rendering Context
    m_hRC = ::wglCreateContext (m_pDC->GetSafeHdc ());
    //Failure to Create Rendering Context
    if(m_hRC == 0)
    {
        MessageBox("Error Creating RC");
        return FALSE;
    }
    //Make the RC Current
    if(::wglMakeCurrent (m_pDC->GetSafeHdc (), m_hRC)==FALSE)
    {
        MessageBox("Error making RC Current");
        return FALSE;
    }
    //Specify Black as the clear color
    ::glClearColor(0.0f,0.0f,0.0f,0.0f);
    //Specify the back of the buffer as clear depth
    ::glClearDepth(1.0f);
    //Enable Depth Testing
    ::glEnable(GL_DEPTH_TEST);
    return TRUE;
}
//Setup Pixel Format
/////////////////////////////////////////////////////////////////////////////
BOOL CCY457OpenGLView::SetupPixelFormat()
{
  static PIXELFORMATDESCRIPTOR pfd = 
    {
        sizeof(PIXELFORMATDESCRIPTOR),  // size of this pfd
        1,                              // version number
        PFD_DRAW_TO_WINDOW |            // support window
        PFD_SUPPORT_OPENGL |            // support OpenGL
        PFD_DOUBLEBUFFER,                // double buffered
        PFD_TYPE_RGBA,                  // RGBA type
        24,                             // 24-bit color depth
        0, 0, 0, 0, 0, 0,               // color bits ignored
        0,                              // no alpha buffer
        0,                              // shift bit ignored
        0,                              // no accumulation buffer
        0, 0, 0, 0,                     // accum bits ignored
        16,                             // 16-bit z-buffer
        0,                              // no stencil buffer
        0,                              // no auxiliary buffer
        PFD_MAIN_PLANE,                 // main layer
        0,                              // reserved
        0, 0, 0                         // layer masks ignored
    };
    int m_nPixelFormat = ::ChoosePixelFormat(m_pDC->GetSafeHdc(), &pfd);
    if ( m_nPixelFormat == 0 )
    {
       return FALSE;
    }
    if ( ::SetPixelFormat(m_pDC->GetSafeHdc(), m_nPixelFormat, &pfd) == FALSE)
    {
       return FALSE;
    }
    return TRUE;
}

6, 在OnSize()中一般用來(lái)設(shè)置視口和視錐，因?yàn)檫@些是和窗口大小相關(guān)的。基本操作包括設(shè)置視口，選擇投影矩陣，設(shè)置模型視圖矩陣。

void CCY457OpenGLView::OnSize(UINT nType, int cx, int cy) 
{
    CView::OnSize(nType, cx, cy);
    GLdouble aspect_ratio; // width/height ratio
    
    if ( 0 >= cx || 0 >= cy )
    {
        return;
    }
    // select the full client area
    ::glViewport(0, 0, cx, cy);
    // compute the aspect ratio
    // this will keep all dimension scales equal
    aspect_ratio = (GLdouble)cx/(GLdouble)cy;
    // select the projection matrix and clear it
    ::glMatrixMode(GL_PROJECTION);
    ::glLoadIdentity();
    // select the viewing volume
    ::gluPerspective(45.0f, aspect_ratio, .01f, 200.0f);
    
    // switch back to the modelview matrix and clear it
    ::glMatrixMode(GL_MODELVIEW);
    ::glLoadIdentity();
}

7,在繪制場(chǎng)景時(shí)，一般包括如下步驟：1）清空緩存。2）繪制場(chǎng)景。3）Flush掉渲染流水線。4）若設(shè)置了雙緩沖，則交換前后臺(tái)緩沖區(qū)。

void CCY457OpenGLView::OnDraw(CDC* pDC)
{
    CCY457OpenGLDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    // Clear out the color & depth buffers
    ::glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    RenderScene();
    // Tell OpenGL to flush its pipeline
    ::glFinish();
    // Now Swap the buffers
    ::SwapBuffers( m_pDC->GetSafeHdc() );
}
void CCY457OpenGLView::RenderScene ()
{//第一個(gè)玩具嘛，先空著，后面慢慢填
}

8，試試改變窗口的大小，你會(huì)看到很嚴(yán)重的閃爍，并且關(guān)閉程序后會(huì)報(bào)告內(nèi)存泄露，因此我們這就來(lái)解決這兩個(gè)問(wèn)題吧。

發(fā)生閃爍的原因是Windows先繪制背景，然后再是OpenGL繪制，因?yàn)槲覀円呀?jīng)讓OpenGL負(fù)責(zé)清空背景色，因此我們不需要Windows去清空背景了

BOOL CCY457OpenGLView::OnEraseBkgnd(CDC* pDC) 
{
    //Tell Windows not to erase the background
    return TRUE;
}

     內(nèi)存泄露的原因是我們?cè)?/span>SetupPixelFormat（）中使用了new運(yùn)算符來(lái)為CClientDC對(duì)象分配內(nèi)存，因此需要顯示delete掉。

void CCY457OpenGLView::OnDestroy() 
{
    CView::OnDestroy();
    //Make the RC non-current
    if(::wglMakeCurrent (0,0) == FALSE)
    {
        MessageBox("Could not make RC non-current");
    }
    
    //Delete the rendering context
    if(::wglDeleteContext (m_hRC)==FALSE)
    {
        MessageBox("Could not delete RC");
    }
    //Delete the DC
    if(m_pDC)
    {
        delete m_pDC;
    }
    //Set it to NULL
    m_pDC = NULL;
}