《基于MFC的OpenGL编程》Part 2 Setting up OpenGL on Windows

最新推荐文章于 2018-01-07 13:12:25 发布

最新推荐文章于 2018-01-07 13:12:25 发布 · 92 阅读

本文详细介绍如何在MFC SDI应用程序中集成OpenGL，包括下载所需文件、设置开发环境、实现像素格式、绘制上下文及设备上下文等关键步骤。

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：

// OpenGLHeaders

#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。

BOOLCCY457OpenGLView::PreCreateWindow(CREATESTRUCT & cs)
{
// TODO:ModifytheWindowclassorstylesherebymodifying
// theCREATESTRUCTcs
// AnOpenGLWindowmustbecreatedwiththefollowingflags
cs.style |= WS_CLIPSIBLINGS | WS_CLIPCHILDREN;
return CView::PreCreateWindow(cs);
}

4,在CCY457OpenGLView.h中加入如下语句：

HGLRCm_hRC; // RenderingContext
CDC * m_pDC; // DeviceContext
BOOLInitializeOpenGL(); // InitializeOpenGL
BOOLSetupPixelFormat(); // SetupthePixelFormat
void RenderScene(); // RendertheScene

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(LPCREATESTRUCTlpCreateStruct)
{
if (CView::OnCreate(lpCreateStruct) == - 1 )
return - 1 ;
// InitializeOpenGLHere
InitializeOpenGL();
return 0 ;
}

BOOLCCY457OpenGLView::InitializeOpenGL()
{
// GetaDCfortheClientArea
m_pDC = new CClientDC( this );
// FailuretoGetDC
if (m_pDC == NULL)
{
MessageBox( " ErrorObtainingDC " );
return FALSE;
}
// Failuretosetthepixelformat
if ( ! SetupPixelFormat())
{
return FALSE;
}
// CreateRenderingContext
m_hRC = ::wglCreateContext(m_pDC -> GetSafeHdc());
// FailuretoCreateRenderingContext
if (m_hRC == 0 )
{
MessageBox( " ErrorCreatingRC " );
return FALSE;
}
// MaketheRCCurrent
if (::wglMakeCurrent(m_pDC -> GetSafeHdc(),m_hRC) == FALSE)
{
MessageBox( " ErrormakingRCCurrent " );
return FALSE;
}
// SpecifyBlackastheclearcolor
::glClearColor( 0.0f , 0.0f , 0.0f , 0.0f );
// Specifythebackofthebufferascleardepth
::glClearDepth( 1.0f );
// EnableDepthTesting
::glEnable(GL_DEPTH_TEST);
return TRUE;
}
// SetupPixelFormat
/////////////////////////////////////////////////////////////////////////// //
BOOLCCY457OpenGLView::SetupPixelFormat()
{
static PIXELFORMATDESCRIPTORpfd =
{
sizeof (PIXELFORMATDESCRIPTOR), // sizeofthispfd
1 , // versionnumber
PFD_DRAW_TO_WINDOW | // supportwindow
PFD_SUPPORT_OPENGL | // supportOpenGL
PFD_DOUBLEBUFFER, // doublebuffered
PFD_TYPE_RGBA, // RGBAtype
24 , // 24-bitcolordepth
0 , 0 , 0 , 0 , 0 , 0 , // colorbitsignored
0 , // noalphabuffer
0 , // shiftbitignored
0 , // noaccumulationbuffer
0 , 0 , 0 , 0 , // accumbitsignored
16 , // 16-bitz-buffer
0 , // nostencilbuffer
0 , // noauxiliarybuffer
PFD_MAIN_PLANE, // mainlayer
0 , // reserved
0 , 0 , 0 // layermasksignored
};
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(UINTnType, int cx, int cy)
{
CView::OnSize(nType,cx,cy);
GLdoubleaspect_ratio; // width/heightratio

if ( 0 >= cx || 0 >= cy)
{
return ;
}
// selectthefullclientarea
::glViewport( 0 , 0 ,cx,cy);
// computetheaspectratio
// thiswillkeepalldimensionscalesequal
aspect_ratio = (GLdouble)cx / (GLdouble)cy;
// selecttheprojectionmatrixandclearit
::glMatrixMode(GL_PROJECTION);
::glLoadIdentity();
// selecttheviewingvolume
::gluPerspective( 45.0f ,aspect_ratio,.01f, 200.0f );

// switchbacktothemodelviewmatrixandclearit
::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);
// Clearoutthecolor&depthbuffers
::glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
RenderScene();
// TellOpenGLtoflushitspipeline
::glFinish();
// NowSwapthebuffers
::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

BOOLCCY457OpenGLView::OnEraseBkgnd(CDC * pDC)
{
// TellWindowsnottoerasethebackground
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。

void CCY457OpenGLView::OnDestroy()
{
CView::OnDestroy();
// MaketheRCnon-current
if (::wglMakeCurrent( 0 , 0 ) == FALSE)
{
MessageBox( " CouldnotmakeRCnon-current " );
}

// Deletetherenderingcontext
if (::wglDeleteContext(m_hRC) == FALSE)
{
MessageBox( " CouldnotdeleteRC " );
}
// DeletetheDC
if (m_pDC)
{
deletem_pDC;
}
// SetittoNULL
m_pDC = NULL;
}