【转】《基于MFC的OpenGL编程》Part 2 Setting up OpenGL on Windows（2）

5, 在OnCreate中我们将通过建立像素格式和绘制上下文来初始化OpenGL. 在InitializeOpenGL()中会创建一个设备上下文(DC)，为这个DC选择一个像素格式，创建和这个DC相关的绘制上下文（RC）,然后选择这个RC.这个函数会调用SetupPixelFormat()来建立像素格式。

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()中一般用来设置视口和视锥，因为这些是和窗口大小相关的。基本操作包括设置视口，选择投影矩阵，设置模型视图矩阵。

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,在绘制场景时，一般包括如下步骤：1）清空缓存。2）绘制场景。3）Flush掉渲染流水线。4）若设置了双缓冲，则交换前后台缓冲区。

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
     ::glFlush();
    // Now Swap the buffers
     ::SwapBuffers( m_pDC->GetSafeHdc() );
}
void CCY457OpenGLView::RenderScene ()
{//第一个玩具嘛，先空着，后面慢慢填
}

8，试试改变窗口的大小，你会看到很严重的闪烁，并且关闭程序后会报告内存泄露，因此我们这就来解决这两个问题吧。

发生闪烁的原因是Windows先绘制背景，然后再是OpenGL绘制，因为我们已经让OpenGL负责清空背景色，因此我们不需要Windows去清空背景了

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

      内存泄露的原因是我们在SetupPixelFormat（）中使用了new运算符来为CClientDC对象分配内存，因此需要显式delete掉。

void CCY457OpenGLView::OnDestroy()
{
     CView::OnDestroy();
    //Make the RC non-current
    if(::wglMakeCurrent (NULL, NULL) == 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;
}