《基于MFC的OpenGL编程》Part 2 Setting up OpenGL on Windows
源代码下载：OpenGL_ch2.rar
WGL – Windows的 OpenGL扩展层
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.
设备上下文
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.
绘制上下文
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.
举个例子，若像素格式只支持很少一部分颜色值，则OpenGL在用RGB值(128,120,135)绘制一个像素时，就可能使用转换后的值(128,128,128)来绘制.
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.
第一个基于MFC的OpenGL应用程
开发环境：VC6.0
1， 首先下载需要的GLUT头文件,DLL和Lib文件，下载链接: glutdlls37beta.zip (149 kilobytes),解压缩后把gltu.h放到"VC98/Include/GL"下，把glut.lib和glut32.lib放到"VC9/Lib" 下，glut32.dll和glut.dll放到你创建的应用程序的运行目录下
2， 创建一个MFC SDI应用程序，在项目属性中加入所需要链接的库文件
1， 在stdafx.h中加入下列语句：
#include <gl/gl.h>
#include <gl/glu.h>
#include <gl/glut.h>
#include <gl/glaux.h>
2， 打开ClassWizard,选择CCY457OpenGLView类，为下述消息加入消息处理函数：WM_CREATE (for OnCreate), WM_DESTROY (for OnDestroy), WM_SIZE (for OnSize), WM_ERASEBACKGROUND (for OnEraseBkground).
3,在窗口创建之前我们必须设置窗口风格包含WS_CLIPCHILDREN和 WS_CLIPSIBLINGS，从而避免OpenGL绘制到其他窗口中去。这些应该放在PreCreateWindow()中。
{
// 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中加入如下语句：
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。
{
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。
{
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。
{
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
{
//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，因此需要显示delete掉。
{
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;
}
