Reflections

Adding reflections to a program too can improve its realism to a great extent. Here we'll look at a simple method to create reflection where we simply redraw the object with an appropriate transformation and make the surface in between translucent. This creates an effective illusion of reflection!!

1,设置光源代码修改如下：

2,绘制函数修改如下：

Selection is a powerful feature of OpenGL that allows you click at some position of the OpenGL window using the mouse and determine which of your objects lie beneath it. The act of selecting a specific object is called Picking. With OpenGL's selection feature, we can specify a viewing volume and determine which objects fall within that viewing volume. A powerful utility function, gluPickMatrix, produces a matrix which can be used to create a smaller viewing volume placed beneath the mouse cursor. Then we use selection to test this viewing volume to see which objects are contained by it.

Selection is actually a rendering mode, but in this mode no pisels are actually copied onto the frame buffer. Instead, primitives drawn within the viewing volume produce hit records in a selection buffer. We must set up this selection buffer in advance and name the primitives or groups of primitives so that they can be identified in the selection buffer.We can then parse the buffer to determine which objects intersected the viewing volume.

Naming Primitives

We have to name a group of primitives such as one describing a cube or a cylinder etc in order to identify them. These names are nothing but integers such as for display list names. The names list is maintained on the named stack. After we initialize the name stack we can push names on the stack or simply replace the name currently on the top of the stack. When a hit occurs during selection, all the names on the stack are copied onto the selection buffer.

1,在CCY457OpenGLView类中加入一个变量，用来表示宽高比

2，OnSize函数修改如下：

3，绘制函数修改如下：

4，加入对鼠标左键选择物体的处理

      Quadrics

Every quadric has a few settings associated with it. We have to create a quadric first and then customize its settings to render the shape we want. The gluNewQuadric function creates a state variable that describes the current drawing style, orientation, lighting mode, texturing mode and the callback functions. Once we use this function to create a new quadric, we can customize the drawing of shapes by changing its state using functions such as

gluQuadricDrawStyle - which selects the type of OpenGL drawing primitives that are used to drw the shape.

gluQuadricOrientation - which controls the direction of the lighting normals.

gluQuadricNormals - which controls the generation of lighting normals.

gluQuadricTexture - which generates texture coordinates automatically for the quadric.

1,在CCY457OpenGLView类中加入下列变量，用来表示二次曲面类型：

2，加入四个控制二次曲面类型的菜单项及其事件处理函数

3,绘制函数修改如下：

The wglUseFontBitmaps() function creates a set of bitmap display lists based on the glyphs in the currently selected font in the current DC for use in the current OpenGL RC. It basically creates a series of sequential display lists which can be executed using the function glCallLists. The function takes care of aligning the raster positions of subsequent bitmaps once we specify the raster position for the first bitmap. We use the glRasterPos function to set the current raster position, where the bitmapped text would start appearing.

The  glRasterPos function works exactly the same way as glVertex function, the only difference being that the position is being transformed and not the object. Thus when we use wglUseFontBitmaps to generate display lists and then call them, the resulting text is displayed, starting at the current raster position, and the bitmaps are copied to the raster buffer, giving the effect of always having the text positioned in the xy plane of the screen. 

Thus we would use wglUseFontBitmaps when we need the text to be visible to the user and that the size of the text relative to its distance from the viewpoint doesn't matter.

wglUseFontOutlines函数

The wglUseFontOutlines function creates a set of 3D polygon or line based primitive display lists, based on the glyphs in the currently selected TrueType font in the current DC for use in the current OpenGL RC. Stroke and Raster fonts are not supported. These objects can then be used to draw 3D characters. This function also has additional arguments that control the extrusion of the 3D characters in the +Z direction, the deviation of the generated primitive vertices from the design outline of the font, whether to generated filled polygons or a wireframe primitives and an array of structures to hold the metrics of each of the generated characters.

1，在CCY457OpenGLView类中加入下述变量：

并在构造函数中进行初始化：

2，加入两个用来创建文本的菜单项及其事件处理函数

3,实际创建2D和3D文本列表的函数:

4, InitializeOpenGL函数中调用上述两个函数：

5，绘制函数修改如下：

显示列表

OpenGL provides a facility to create a preprocessed set of OpenGL commands called a display list. Creating a display list is a straight forward process. We just have to delimit the display list code with glNewList and glEndList. The display list is named by an integer and this name is used to call the list to be executed later on. Display lists are very useful for scenes which have lot of geometry that don't change in from frame to frame. If we have to rerender something that doesn't change it is not worth going through all the calculations required once again - it is better to store them somewhere in memory and reuse it. This is exactly what the display list lets us achieve. Thus if we are going to repeatedly execute the same sequence of OpenGL commands we can create and store a display list and then have this cached sequence of calls repeated with minimal overhead, since all the vertices, lighting calculations, textures and matrix operations are calculated only when the list is created and not when it is replayed. Only the results of the calculations end up being stored in display lists. This means we cannot modify the list once we create it.

1,CY457OpenGLView类中加入一个变量来保存显示列表名称

2,创建显示列表

3，在InitializeOpenGL函数中加入对上述函数的调用：

4，修改RenderScene的绘制代码

Texture Mapping

Texture Mapping in OpenGL is a fairly straightforward concept. Every texture is nothing but an image of some sort. Texture mapping is basically applying a texture to a surface. Textures can be 1D, 2D or even 3D. A 1D texture is an image with either a width or a height, not both. They are not very useful. 2D textures have both width and height and are very useful. 3D textures are called Volume textures and are used in medical imaging applications for viewing CAT, MRI, and other 3D scans. We will look at using 2D textures in OpenGL as they are the most widely used in 3D Graphics.

Windows Bitmap Files

Images in Windows are typically stored in bitmap files. These images can be used as textures that will be applied to OpenGL surfaces. But before use them for texture mapping applications we should convert them to an OpenGL format. So we essentially have to read a Windows Bitmap into an OpenGL image. We can use the Auxiliary library to do so. It takes care of all the trouble involved in performing this conversion. Once a texture map is read into memory, the individual elements are called texels, just like an image's individual elements are called pixels. We wouldn't be dealing with these texels as we would be using the Aux library routine auxDIBImageLoadA to perform the conversion for us. Also, we need to make sure that the image dimensions are a power of 2. OpenGL images that we are going to use as a texture must have dimensions of a power of 2. Thus 32X32, 64X64, 128X64 etc. are all valid image sizes to be used as texture maps.

Defining 2D Textures

To define a 2D texture image in OpenGL we call glTexImage2D (when we are not using Mipmapping).

Mipmapping

When texture mapping is used with animation scaling of images cause some visual artifacts. This can be avoided by generating textures of various sizes from a large original texture and letting OpenGL automatically switch between the textures of various sizes. This technique is called Mipmapping and the individual textures are called Mipmaps. We can use the function gluBuild2DMipMaps to construct a series of mipmaps.

Texture Modes

OpenGL defines three texturing modes for different types of rendering. The first is GL_MODULATE, which modulates the current lighting and color information with the texture image. GL_DECAL is the second mode which only uses the texture image. Color and Lighting information will not affect the texture's appearance. The last mode is GL_BLEND, in which the texture image is blended with the current texture color and the current lighting and color information.

Texture Filters

OpenGL uses texture filters to interpolate between the texture pixels. It provides two types of texture filters: the minification filter (GL_TEXTURE_MIN_FILTER) for polygons smaller than the texture image and the magnification filter (GL_TEXTURE_MAG_FILTER) for polygons that are larger than the texture image. We'll look at how we will use these later in the tutorial.

Texture Coordinates

Texture Coordinates associate a particular location in the texture image with vertices in a polygon. These coordinates determine how the texture is mapped onto the polygon. Texture coordinates lie between 0.0 and 1.0 in case of 2D textures.

Texture Wrapping

When texture coordinates go outside the range of 0.0 to 1.0, they are either clamped to the surface or repeated. This can be specified by setting the GL_TEXTURE_WRAP_* parameter appropriately, to either GL_CLAMP or GL_REPEAT.

Texture Objects

Texture objects are a way of loading and maintaining multiple textures in memory without loading them each time before they are used. They are an optimization feature introduced recently in OpenGL.

1,在CCY457OpenGLView类中加入下列变量，分别代表纹理环绕，纹理过滤，纹理模式的参数。

 并在构造函数中加入：

2,加载纹理对象。

 3,加入控制纹理映射效果的各个菜单项及其事件处理程序

4，在InitializeOpenGL()中加入如下调用：

5，绘制函数修改如下：

Blending in OpenGL provides pixel-level control of RGBA color storage in the color buffer. To enable blending we must first call glEnable(GL_BLEND). We have to set up the blending function glBlendFunc with two arguments: the source and the destination colors. By default these are GL_ONE and GL_ZERO respectively, which is equivalent to glDisable(GL_BLEND). The blend functions are applied to the source color set by glColor and destination color in the color buffer. The results of the blending functions are added together to generate the new color value which is put onscreen.

Transparency is perhaps the most typical use of blending. In order to produce transparency we should set up the blending function as follows - glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA). This combination takes the source color, scales it based on the alpha component and then adds the destination pixel color scaled by 1 minus the alpha value. It basically takes a fraction of the current drawing color and overlays it on the pixel on the screen. The alpha component can be from 0 (completely transparent) to 1 (completely opaque).

Anti-Aliasing

You might have noticed in some of your OpenGL pictures that lines, especially nearly horizontal or nearly vertical ones, appear jagged. These jaggies appear because the ideal line is approximated by a series of pixels that must lie on the pixel grid. The jaggedness is called aliasing. Antialiasing can be enabled by calling the function - glEnable(GL_POLYGON_SMOOTH) for polygons.

Fog

An entire image can be made to appear more natural by adding fog, which makes objects fade into the distance. Fog is a general term that describes similar forms of atmospheric effects; it can be used to simulate haze, mist, smoke, or pollution. Fog is essential in visual-simulation applications, where limited visibility needs to be approximated.

When fog is enabled, objects that are farther from the viewpoint begin to fade into the fog color. You can control the density of the fog, which determines the rate at which objects fade as the distance increases, as well as the fog's color. Since fog is applied after matrix transformations, lighting, and texturing are performed, it affects transformed, lit, and textured objects.

Using fog is easy. Enable it by passing GL_FOG to glEnable(), and you choose the color and the equation that controls the density with glFog*().

1,在CCY457OpenGLView类中加入下列布尔变量，分别代表是否开启混合，雾和反锯齿效果。

Code
    //Effects
    BOOL m_blend;
    BOOL m_fog;
    BOOL m_antialias;

并在构造函数中对其初始化：

2，加入控制上述三种效果的菜单项及其事件处理函数

3，在InitializeOpenGL函数中对雾效果进行设置。

Materials

OpenGL materials are description of what objects are made of. It basically specifies how much of light they reflect and this is what we would be seeing. OpenGL lighting goes a long way towards modeling real world lighting. In order achieve proper lighting effects in OpenGL we need to specify material properties. Material properties are of the following types - Diffuse and Ambient properties, Specular and Shininess Properties and Emissive Properties. These are the properties that specify how a surface dissipates light.

Diffuse and Ambient Properties

The diffuse and ambient reflective material properties are a type of reflective effect that is independent of the viewpoint. Diffuse lighting is light from a particular direction and ambient lighting is light that is coming from all directions. A particular light source can have both a diffuse and an ambient component. These material properties describe how the material reflects diffuse and ambient light falling on it.

Specular and Shininess Properties

The specular and the shininess properties of the surface describe the reflective effects that are affected by the position of the viewpoint. Specular light is reflected from a surface that produces the reflective highlights in a surface. The shininess is a value that describes how focussed the reflective properties are.

Emissive Property

This is the light that an object gives off by itself. A typical example of this is a light source itself.

Specifying a material property

In order to specify a material property we have to use the OpenGL function - glMaterial*(). We can individually specify the material properties using this function. Another way to go about this is by color tracking. This can be achieved by enabling color tracking and specifying what parameters of the material would be affected by the glColor command. This is an optimization feature that OpenGL provides and is useful in cases where we will be changing only particular properties of the material and not all of them. In this tutorial we will use glMaterial to specify the material properties as we will be individually setting each one of them.

Choosing the material properties determine how the object will look. We will follow the following steps in choosing the material properties -

• Decide on the diffuse and ambient colors.
• Decide on the shininess depending on the type of material object that is being modeled such as silver, wood etc.
• Decide whether the object would be giving off any light on its own.

The above values can be obtained by mere trial and error. We will look at how we go about doing this when we write a program.

Lighting

OpenGL has two types of lighting: global lighting or ambient lighting and individual light sources which have position and direction. The way an object is lit depends on the material of the object, all the lights and their properties, their positions and direction etc. This means lighting calculations are quite expensive and are hence turned off by OpenGL by default. So we have to turn on lighting before using it. Global lighting parameters can be set using the glLightModel function which specify the lighting model we would be using - such as an infinite viewer or a local viewer (for specular highlights), single sided or two sided lighting and the RGBA value for the ambient light. In addition to this we would be specifying the individual light sources.  

1，设置灯光和材质属性

2，在初始化OpenGL时调用上述函数

Smooth Shading and Flat Shading  

When Smooth Shading is specified, the color values are interpolated between vertices. If Flat Shading is specified, one vertex is selected as being representative of all the vertices, thus the entire primitive is displayed using one single color. 

一个简单Demo

1,在CCY457OpenGLView.h中加入如下旋转控制变量：

 并在构造函数中初始化：

2，在OnTimer函数中，修改绕x,y轴旋转的角度值

3,加入两个菜单项，控制OpenGL的渲染模式

4，在RenderScene中加入绘制代码：

      加入动画效果最容易的方法是响应WM_TIMER消息，在其消息处理函数中改变一些参数值，比如每过多少毫秒就旋转一定的角度，并且重绘场景。

Frame Rate

Frame rate is nothing but the number of frames that can be rendered per second. The higher this rate, the smoother the animation. In order to calculate the frame rate we retrieve the system time (using the Windows multimedia API function timeGetTime()) before the rendering is performed and after the buffer is swapped. The difference between the two values is the elapsed time to render one frame. Thus we can calculate the frame rate for a given application.

1，我们需要调用timeGetTime（）函数,因此在stdafx.h中加入:

并且Link—>Object/library modules中加入winmm.lib

2，为了计算绘制用时，在CCY457OpenGLView.h中加入如下变量：

并在构造函数中进行初始化：

3，为了计算帧速率，修改OnCreate函数，在其中获取窗口标题，从标题中去掉”Untitled”字样，并启动定时器；

4，同样为了计算帧速率，修改OnDraw函数如下，在其中用glPushMatrix 和 glPopMatrix将RenderScene函数包裹起来，从而确保动画会正确运行。在SwapBuffers调用后我们调用PostRenderScene来显示帧速率信息到窗口标题。

4，在CCY457OpenGLView类中加入下述成员函数，用来显示帧速率信息到窗口标题

5，在OnTimer函数中，通过增加变量DayOfYear 和 HourOfDay的值来控制地球和月球的位置，并且调用InvalidateRect来刷新界面。

6，在RenderScene中加入绘制代码：

1,首先在CCY457OpenGLView类中为WM_KEYDOWN,  WM_LBUTTONDOWN, WM_LBUTTONUP 和 WM_MOUSEMOVE四个事件加入事件处理函数。

2,在CCY457OpenGLView.h中加入下列用于控制旋转和移动的变量：

并在构造函数中初始化：

3，加入绘制代码：

4，为四个事件处理函数加入控制代码

Translation is nothing but moving along an arbitrary axis. Rotation is spinning about an arbitrary axis. Scaling is increase or decrease in size along an arbitrary axis. One important point to remember is that OpenGL uses a right hand coordinate system where Z-ve goes into the Screen. An object said to be undergoing a transformation could be undergoing a translation, rotation and/or scaling. Understanding how different types of transformations work together is very important.

本文将对地球进行建模，让其围绕着太阳，此外它还会有月球伴随,而在下文中将会加入对鼠标和键盘的事件响应机制。

绘制代码

Viewing Volume is nothing but the region of 3D Cartesian space in that will occupy the window. It is nothing but the minimum and maximum x, y and z values that are inside the window. So if a vertex is outside this range of x, y and z values then they are clipped by OpenGL before rendering can occur.

Z Buffer

The new term we have to deal with in addition to width and height of an object in 3D graphics is depth. The depth of an object is its distance from the viewpoint. The viewpoint is the location from which we are looking at that point. This depth value goes into the depth or Z-buffer. If we are drawing 2 objects that have some pixels that overlap, the first object will after it is rendered have its depth value in the depth buffer. When the next object is rendered, OpenGL will check to see whether the pixel it’s about to draw is in front of (with respect to the viewpoint) any pixel from the first object that’s already drawn. It does this by checking the Z value of the current pixel with the value that is already in the buffer. If the new pixel is closer to the viewpoint, OpenGL places its depth value in the depth buffer. This is how the Z-buffer works.

正交投影和透视投影

One term we need to understand very well to learn 3D Graphics well is projection. Well, computer graphics at its simplest is all about setting a color to a pixel on screen. And a pixel on a screen can have only two dimensions. So 3D graphics is merely an illusion. The 3D coordinates that we specify will have to be projected onto a 2D surface to create this illusion for us. And we have to specify how this projection works. By specifying a projection we specify the clipping or viewing volume.

基本3D图形绘制

1,在CCY457OpenGLView.h中加入下列变量

并且在构造函数中初始化

2,加入五个菜单项及其对应的事件处理程序。

3，由于开始绘制3维图形，因此使用第一篇文章的OnSize()函数。

4，在RenderScene中加入具体的绘制代码：

     In OpenGL when you create a window to draw in we must specify the coordinate system we want to use and how to map the specified coordinates into physical screen coordinates. We would be using the 2D Cartesian coordinate system with the origin 0,0 at the centre of the screen. Before we can start plotting points, lines and shapes in a window we must also specify how to translate coordinate pairs into screen coordinates, by specifying the clipping area i.e the region of Cartesian space that occupies the window. 

视口

The clipping area height and width will rarely match the width and height of the window in pixels. The coordinate system must therefore be mapped from logical Cartesian coordinates to physical screen coordinates. This mapping is specified by a setting known as the viewport, which is the region within the window's client area that is used for drawing the clipping area. 

顶点和基本图元

A vertex is nothing more than a coordinate in 2D or 3D space. In both 2D and 3D, when we draw an object we compose it with several smaller shapes called primitives which as 1 or 2 dimensional entities such as points, lines, and polygons. Each corner of an object composed of primitives is a vertex

基本图形绘制程序

1,在CCY457OpenGLView.h中加入下列变量：

2,并且加入四个菜单项及其对应的事件处理程序。

3,修改第二篇文章中的OnSize()函数，因为本文中只绘制2维图形.

4,在RenderScene中加入具体的绘制代码：

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：

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。

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中加入如下语句：

    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
    ::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

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;
}

 

Perspective

Perspective refers to the angles between the lines that lend the illusion of three dimensions.

Colors and Shading

Moving beyond line drawing, we need to add color to create a solid object. Shading refers to the way the color is applied to the polygon. Shading can be of two types in OpenGL - Flat or Smooth.

Lights and Shadows

Plain solid color doesn’t offer enough realism. By applying Lighting effects we can make objects appear as they would in reality depending on their material properties and the lighting parameters. Adding a shadow further increases realism.

Texture Mapping

With Texture Mapping we can have wood grains, cloth textures, brick like textures etc instead of plain materials. This technique of applying an image to the surface of a polygon is called Texture Mapping. The image we use is called the Texture and the individual elements of the texture are called Texels.

Fog

Fog is an atmospheric effect that adds haziness to objects in a scene depending on how far the objects are from the viewer.

Blending and Transparency

Blending is the combination of colors of objects on the screen. This effect can be used for a variety of purposes. By varying the amount each object is blended with the scene we can make objects look transparent.

Anti-Aliasing