OpenGL入门笔记（七）

OpenGL中的绝大多数特效都与某些类型的（色彩）混合有关。混色的定义为，将某个象素的颜色和已绘制在屏幕上与其对应的象素颜色相互结合。至于如何结合这两个颜色则依赖于颜色的alpha通道的分量值，以及/或者所使用的混色函数。Alpha通常是位于颜色值末尾的第4个颜色组成分量。前面这些课我们都是用GL_RGB来指定颜色的三个分量。相应的GL_RGBA可以指定alpha分量的值。更进一步，我们可以使用glColor4f()来代替glColor3f()。

　　 绝大多数人都认为Alpha分量代表材料的透明度。这就是说，alpha值为0.0时所代表的材料是完全透明的。alpha值为1.0时所代表的材料则是完全不透明的。

混合的基本原理是就将要分色的图像各象素的颜色以及背景颜色均按照RGB规则各自分离之后，根据 — 图像的RGB颜色分量*alpha值+背景的RGB颜色分量*(1-alpha值) — 这样一个简单公式来混合之后，最后将混合得到的RGB分量重新合并。）公式如下：

(Rs Sr + Rd Dr, Gs Sg + Gd Dg, Bs Sb + Bd Db, As Sa + Ad Da)

　　 OpenGL按照上面的公式计算这两个象素的混色结果。小写的s和r分别代表源象素和目标象素。大写的S和D则是相应的混色因子。这些决定了您如何对这些象素混色。绝大多数情况下，各颜色通道的alpha混色值大小相同，这样对源象素就有(As, As, As, As)，目标象素则有(1, 1, 1, 1) - (As, As, As, As)。上面的公式就成了下面的模样：

 

(Rs As + Rd (1 - As), Gs As + Gd (1 - As), Bs As + Bs (1 - As), As As + Ad (1 - As))

这个公式会生成透明/半透明的效果。

 

在OpenGL中首先我们得打开混合， 然后设置混合式。在绘制透明物体的时候， 我们关闭深度缓存， 因为我们仍然希望在半透明物体后面的物体能被绘制。 这并不是使用混合的正确方式， 但是在情况简单的时候它会工作得很好。正确的混色过程应该是先绘制全部的场景之后再绘制透明的图形。并且要按照与深度缓存相反的次序来绘制（先画最远的物体）。考虑对两个多边形（1和2）进行alpha混合，不同的绘制次序会得到不同的结果。（这里假定多边形1离观察者最近，那么正确的过程应该先画多边形2，再画多边形1。正如您再现实中所见到的那样，从这两个“透明的”多边形背后照射来的光线总是先穿过多边形2，再穿过多边形1，最后才到达观察者的眼睛）。 在深度缓存启用时，您应该将透明图形按照深度进行排序，并在全部场景绘制完毕之后再绘制这些透明物体。否则您将得到不正确的结果。

demo8
#include <windows.h>        // Header File For Windows
#include <stdio.h>            // Header File For Standard Input/Output
#include <gl\gl.h>            // Header File For The OpenGL32 Library
#include <gl\glu.h>            // Header File For The GLu32 Library
#include <gl\glaux.h>        // Header File For The Glaux Library

HDC            hDC=NULL;        // Private GDI Device Context
HGLRC        hRC=NULL;        // Permanent Rendering Context
HWND        hWnd=NULL;        // Holds Our Window Handle
HINSTANCE    hInstance;        // Holds The Instance Of The Application

bool    keys[256];            // Array Used For The Keyboard Routine
bool    active=TRUE;        // Window Active Flag Set To TRUE By Default
bool    fullscreen=TRUE;    // Fullscreen Flag Set To Fullscreen Mode By Default
bool    light;                // Lighting ON/OFF
bool    blend;                // Blending OFF/ON? ( NEW )
bool    lp;                    // L Pressed?
bool    fp;                    // F Pressed?
bool    bp;                    // B Pressed? ( NEW )

GLfloat    xrot;                // X Rotation
GLfloat    yrot;                // Y Rotation
GLfloat xspeed;                // X Rotation Speed
GLfloat yspeed;                // Y Rotation Speed
GLfloat    z=-5.0f;            // Depth Into The Screen

GLfloat LightAmbient[]=        { 0.5f, 0.5f, 0.5f, 1.0f };
GLfloat LightDiffuse[]=        { 1.0f, 1.0f, 1.0f, 1.0f };
GLfloat LightPosition[]=    { 0.0f, 0.0f, 2.0f, 1.0f };

GLuint    filter;                // Which Filter To Use
GLuint    texture[3];            // Storage For 3 Textures

LRESULT    CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);    // Declaration For WndProc

AUX_RGBImageRec *LoadBMP(char *Filename)                // Loads A Bitmap Image
{
    FILE *File=NULL;                                    // File Handle

    if (!Filename)                                        // Make Sure A Filename Was Given
    {
        return NULL;                                    // If Not Return NULL
    }

    File=fopen(Filename,"r");                            // Check To See If The File Exists

    if (File)                                            // Does The File Exist?
    {
        fclose(File);                                    // Close The Handle
        return auxDIBImageLoad(Filename);                // Load The Bitmap And Return A Pointer
    }

    return NULL;                                        // If Load Failed Return NULL
}

int LoadGLTextures()                                    // Load Bitmaps And Convert To Textures
{
    int Status=FALSE;                                    // Status Indicator

    AUX_RGBImageRec *TextureImage[1];                    // Create Storage Space For The Texture

    memset(TextureImage,0,sizeof(void *)*1);               // Set The Pointer To NULL

    // Load The Bitmap, Check For Errors, If Bitmap's Not Found Quit
    if (TextureImage[0]=LoadBMP("Data/glass.bmp"))
    {
        Status=TRUE;                                    // Set The Status To TRUE

        glGenTextures(3, &texture[0]);                    // Create Three Textures

        // Create Nearest Filtered Texture
        glBindTexture(GL_TEXTURE_2D, texture[0]);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
        glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[0]->sizeX, TextureImage[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);

        // Create Linear Filtered Texture
        glBindTexture(GL_TEXTURE_2D, texture[1]);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
        glTexImage2D(GL_TEXTURE_2D, 0, 3, TextureImage[0]->sizeX, TextureImage[0]->sizeY, 0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);

        // Create MipMapped Texture
        glBindTexture(GL_TEXTURE_2D, texture[2]);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_NEAREST);
        gluBuild2DMipmaps(GL_TEXTURE_2D, 3, TextureImage[0]->sizeX, TextureImage[0]->sizeY, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);
    }

    if (TextureImage[0])                                // If Texture Exists
    {
        if (TextureImage[0]->data)                        // If Texture Image Exists
        {
            free(TextureImage[0]->data);                // Free The Texture Image Memory
        }

        free(TextureImage[0]);                            // Free The Image Structure
    }

    return Status;                                        // Return The Status
}

GLvoid ReSizeGLScene(GLsizei width, GLsizei height)        // Resize And Initialize The GL Window
{
    if (height==0)                                        // Prevent A Divide By Zero By
    {
        height=1;                                        // Making Height Equal One
    }

    glViewport(0,0,width,height);                        // Reset The Current Viewport

    glMatrixMode(GL_PROJECTION);                        // Select The Projection Matrix
    glLoadIdentity();                                    // Reset The Projection Matrix

    // Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);

    glMatrixMode(GL_MODELVIEW);                            // Select The Modelview Matrix
    glLoadIdentity();                                    // Reset The Modelview Matrix
}

int InitGL(GLvoid)                                        // All Setup For OpenGL Goes Here
{
    if (!LoadGLTextures())                                // Jump To Texture Loading Routine
    {
        return FALSE;                                    // If Texture Didn't Load Return FALSE
    }

    glEnable(GL_TEXTURE_2D);                            // Enable Texture Mapping
    glShadeModel(GL_SMOOTH);                            // Enable Smooth Shading
    glClearColor(0.0f, 0.0f, 0.0f, 0.5f);                // Black Background
    glClearDepth(1.0f);                                    // Depth Buffer Setup
    glEnable(GL_DEPTH_TEST);                            // Enables Depth Testing
    glDepthFunc(GL_LEQUAL);                                // The Type Of Depth Testing To Do
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);    // Really Nice Perspective Calculations

    glLightfv(GL_LIGHT1, GL_AMBIENT, LightAmbient);        // Setup The Ambient Light
    glLightfv(GL_LIGHT1, GL_DIFFUSE, LightDiffuse);        // Setup The Diffuse Light
    glLightfv(GL_LIGHT1, GL_POSITION,LightPosition);    // Position The Light
    glEnable(GL_LIGHT1);                                // Enable Light One

    glColor4f(1.0f, 1.0f, 1.0f, 0.5);                    // Full Brightness.  50% Alpha
    glBlendFunc(GL_SRC_ALPHA,GL_ONE);                    // Set The Blending Function For Translucency

    return TRUE;                                        // Initialization Went OK
}

int DrawGLScene(GLvoid)                                    // Here's Where We Do All The Drawing
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    // Clear The Screen And The Depth Buffer
    glLoadIdentity();                                    // Reset The View
    glTranslatef(0.0f,0.0f,z);

    glRotatef(xrot,1.0f,0.0f,0.0f);
    glRotatef(yrot,0.0f,1.0f,0.0f);

    glBindTexture(GL_TEXTURE_2D, texture[filter]);

    glBegin(GL_QUADS);
        // Front Face
        glNormal3f( 0.0f, 0.0f, 1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
        // Back Face
        glNormal3f( 0.0f, 0.0f,-1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
        // Top Face
        glNormal3f( 0.0f, 1.0f, 0.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
        // Bottom Face
        glNormal3f( 0.0f,-1.0f, 0.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
        // Right face
        glNormal3f( 1.0f, 0.0f, 0.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
        // Left Face
        glNormal3f(-1.0f, 0.0f, 0.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
        glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
    glEnd();

    xrot+=xspeed;
    yrot+=yspeed;
    return TRUE;                                        // Keep Going
}

GLvoid KillGLWindow(GLvoid)                                // Properly Kill The Window
{
    if (fullscreen)                                        // Are We In Fullscreen Mode?
    {
        ChangeDisplaySettings(NULL,0);                    // If So Switch Back To The Desktop
        ShowCursor(TRUE);                                // Show Mouse Pointer
    }

    if (hRC)                                            // Do We Have A Rendering Context?
    {
        if (!wglMakeCurrent(NULL,NULL))                    // Are We Able To Release The DC And RC Contexts?
        {
            MessageBox(NULL,"Release Of DC And RC Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
        }

        if (!wglDeleteContext(hRC))                        // Are We Able To Delete The RC?
        {
            MessageBox(NULL,"Release Rendering Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
        }
        hRC=NULL;                                        // Set RC To NULL
    }

    if (hDC && !ReleaseDC(hWnd,hDC))                    // Are We Able To Release The DC
    {
        MessageBox(NULL,"Release Device Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
        hDC=NULL;                                        // Set DC To NULL
    }

    if (hWnd && !DestroyWindow(hWnd))                    // Are We Able To Destroy The Window?
    {
        MessageBox(NULL,"Could Not Release hWnd.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
        hWnd=NULL;                                        // Set hWnd To NULL
    }

    if (!UnregisterClass("OpenGL",hInstance))            // Are We Able To Unregister Class
    {
        MessageBox(NULL,"Could Not Unregister Class.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
        hInstance=NULL;                                    // Set hInstance To NULL
    }
}

/**//*    This Code Creates Our OpenGL Window.  Parameters Are:                    *
 *    title            - Title To Appear At The Top Of The Window                *
 *    width            - Width Of The GL Window Or Fullscreen Mode                *
 *    height            - Height Of The GL Window Or Fullscreen Mode            *
 *    bits            - Number Of Bits To Use For Color (8/16/24/32)            *
 *    fullscreenflag    - Use Fullscreen Mode (TRUE) Or Windowed Mode (FALSE)    */
 
BOOL CreateGLWindow(char* title, int width, int height, int bits, bool fullscreenflag)
{
    GLuint        PixelFormat;            // Holds The Results After Searching For A Match
    WNDCLASS    wc;                        // Windows Class Structure
    DWORD        dwExStyle;                // Window Extended Style
    DWORD        dwStyle;                // Window Style
    RECT        WindowRect;                // Grabs Rectangle Upper Left / Lower Right Values
    WindowRect.left=(long)0;            // Set Left Value To 0
    WindowRect.right=(long)width;        // Set Right Value To Requested Width
    WindowRect.top=(long)0;                // Set Top Value To 0
    WindowRect.bottom=(long)height;        // Set Bottom Value To Requested Height

    fullscreen=fullscreenflag;            // Set The Global Fullscreen Flag

    hInstance            = GetModuleHandle(NULL);                // Grab An Instance For Our Window
    wc.style            = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;    // Redraw On Size, And Own DC For Window.
    wc.lpfnWndProc        = (WNDPROC) WndProc;                    // WndProc Handles Messages
    wc.cbClsExtra        = 0;                                    // No Extra Window Data
    wc.cbWndExtra        = 0;                                    // No Extra Window Data
    wc.hInstance        = hInstance;                            // Set The Instance
    wc.hIcon            = LoadIcon(NULL, IDI_WINLOGO);            // Load The Default Icon
    wc.hCursor            = LoadCursor(NULL, IDC_ARROW);            // Load The Arrow Pointer
    wc.hbrBackground    = NULL;                                    // No Background Required For GL
    wc.lpszMenuName        = NULL;                                    // We Don't Want A Menu
    wc.lpszClassName    = "OpenGL";                                // Set The Class Name

    if (!RegisterClass(&wc))                                    // Attempt To Register The Window Class
    {
        MessageBox(NULL,"Failed To Register The Window Class.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                            // Return FALSE
    }
    
    if (fullscreen)                                                // Attempt Fullscreen Mode?
    {
        DEVMODE dmScreenSettings;                                // Device Mode
        memset(&dmScreenSettings,0,sizeof(dmScreenSettings));    // Makes Sure Memory's Cleared
        dmScreenSettings.dmSize=sizeof(dmScreenSettings);        // Size Of The Devmode Structure
        dmScreenSettings.dmPelsWidth    = width;                // Selected Screen Width
        dmScreenSettings.dmPelsHeight    = height;                // Selected Screen Height
        dmScreenSettings.dmBitsPerPel    = bits;                    // Selected Bits Per Pixel
        dmScreenSettings.dmFields=DM_BITSPERPEL|DM_PELSWIDTH|DM_PELSHEIGHT;

        // Try To Set Selected Mode And Get Results.  NOTE: CDS_FULLSCREEN Gets Rid Of Start Bar.
        if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)!=DISP_CHANGE_SUCCESSFUL)
        {
            // If The Mode Fails, Offer Two Options.  Quit Or Use Windowed Mode.
            if (MessageBox(NULL,"The Requested Fullscreen Mode Is Not Supported By\nYour Video Card. Use Windowed Mode Instead?","NeHe GL",MB_YESNO|MB_ICONEXCLAMATION)==IDYES)
            {
                fullscreen=FALSE;        // Windowed Mode Selected.  Fullscreen = FALSE
            }
            else
            {
                // Pop Up A Message Box Letting User Know The Program Is Closing.
                MessageBox(NULL,"Program Will Now Close.","ERROR",MB_OK|MB_ICONSTOP);
                return FALSE;                                    // Return FALSE
            }
        }
    }

    if (fullscreen)                                                // Are We Still In Fullscreen Mode?
    {
        dwExStyle=WS_EX_APPWINDOW;                                // Window Extended Style
        dwStyle=WS_POPUP;                                        // Windows Style
        ShowCursor(FALSE);                                        // Hide Mouse Pointer
    }
    else
    {
        dwExStyle=WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;            // Window Extended Style
        dwStyle=WS_OVERLAPPEDWINDOW;                            // Windows Style
    }

    AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle);        // Adjust Window To True Requested Size

    // Create The Window
    if (!(hWnd=CreateWindowEx(    dwExStyle,                            // Extended Style For The Window
                                "OpenGL",                            // Class Name
                                title,                                // Window Title
                                dwStyle |                            // Defined Window Style
                                WS_CLIPSIBLINGS |                    // Required Window Style
                                WS_CLIPCHILDREN,                    // Required Window Style
                                0, 0,                                // Window Position
                                WindowRect.right-WindowRect.left,    // Calculate Window Width
                                WindowRect.bottom-WindowRect.top,    // Calculate Window Height
                                NULL,                                // No Parent Window
                                NULL,                                // No Menu
                                hInstance,                            // Instance
                                NULL)))                                // Dont Pass Anything To WM_CREATE
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Window Creation Error.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    static    PIXELFORMATDESCRIPTOR pfd=                // pfd Tells Windows How We Want Things To Be
    {
        sizeof(PIXELFORMATDESCRIPTOR),                // Size Of This Pixel Format Descriptor
        1,                                            // Version Number
        PFD_DRAW_TO_WINDOW |                        // Format Must Support Window
        PFD_SUPPORT_OPENGL |                        // Format Must Support OpenGL
        PFD_DOUBLEBUFFER,                            // Must Support Double Buffering
        PFD_TYPE_RGBA,                                // Request An RGBA Format
        bits,                                        // Select Our 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,                                    // Accumulation Bits Ignored
        16,                                            // 16Bit Z-Buffer (Depth Buffer)  
        0,                                            // No Stencil Buffer
        0,                                            // No Auxiliary Buffer
        PFD_MAIN_PLANE,                                // Main Drawing Layer
        0,                                            // Reserved
        0, 0, 0                                        // Layer Masks Ignored
    };
    
    if (!(hDC=GetDC(hWnd)))                            // Did We Get A Device Context?
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Can't Create A GL Device Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    if (!(PixelFormat=ChoosePixelFormat(hDC,&pfd)))    // Did Windows Find A Matching Pixel Format?
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Can't Find A Suitable PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    if(!SetPixelFormat(hDC,PixelFormat,&pfd))        // Are We Able To Set The Pixel Format?
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Can't Set The PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    if (!(hRC=wglCreateContext(hDC)))                // Are We Able To Get A Rendering Context?
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Can't Create A GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    if(!wglMakeCurrent(hDC,hRC))                    // Try To Activate The Rendering Context
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Can't Activate The GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    ShowWindow(hWnd,SW_SHOW);                        // Show The Window
    SetForegroundWindow(hWnd);                        // Slightly Higher Priority
    SetFocus(hWnd);                                    // Sets Keyboard Focus To The Window
    ReSizeGLScene(width, height);                    // Set Up Our Perspective GL Screen

    if (!InitGL())                                    // Initialize Our Newly Created GL Window
    {
        KillGLWindow();                                // Reset The Display
        MessageBox(NULL,"Initialization Failed.","ERROR",MB_OK|MB_ICONEXCLAMATION);
        return FALSE;                                // Return FALSE
    }

    return TRUE;                                    // Success
}

LRESULT CALLBACK WndProc(    HWND    hWnd,            // Handle For This Window
                            UINT    uMsg,            // Message For This Window
                            WPARAM    wParam,            // Additional Message Information
                            LPARAM    lParam)            // Additional Message Information
{
    switch (uMsg)                                    // Check For Windows Messages
    {
        case WM_ACTIVATE:                            // Watch For Window Activate Message
        {
            if (!HIWORD(wParam))                    // Check Minimization State
            {
                active=TRUE;                        // Program Is Active
            }
            else
            {
                active=FALSE;                        // Program Is No Longer Active
            }

            return 0;                                // Return To The Message Loop
        }

        case WM_SYSCOMMAND:                            // Intercept System Commands
        {
            switch (wParam)                            // Check System Calls
            {
                case SC_SCREENSAVE:                    // Screensaver Trying To Start?
                case SC_MONITORPOWER:                // Monitor Trying To Enter Powersave?
                return 0;                            // Prevent From Happening
            }
            break;                                    // Exit
        }

        case WM_CLOSE:                                // Did We Receive A Close Message?
        {
            PostQuitMessage(0);                        // Send A Quit Message
            return 0;                                // Jump Back
        }

        case WM_KEYDOWN:                            // Is A Key Being Held Down?
        {
            keys[wParam] = TRUE;                    // If So, Mark It As TRUE
            return 0;                                // Jump Back
        }

        case WM_KEYUP:                                // Has A Key Been Released?
        {
            keys[wParam] = FALSE;                    // If So, Mark It As FALSE
            return 0;                                // Jump Back
        }

        case WM_SIZE:                                // Resize The OpenGL Window
        {
            ReSizeGLScene(LOWORD(lParam),HIWORD(lParam));  // LoWord=Width, HiWord=Height
            return 0;                                // Jump Back
        }
    }

    // Pass All Unhandled Messages To DefWindowProc
    return DefWindowProc(hWnd,uMsg,wParam,lParam);
}

int WINAPI WinMain(    HINSTANCE    hInstance,            // Instance
                    HINSTANCE    hPrevInstance,        // Previous Instance
                    LPSTR        lpCmdLine,            // Command Line Parameters
                    int            nCmdShow)            // Window Show State
{
    MSG        msg;                                    // Windows Message Structure
    BOOL    done=FALSE;                                // Bool Variable To Exit Loop

    // Ask The User Which Screen Mode They Prefer
    if (MessageBox(NULL,"Would You Like To Run In Fullscreen Mode?", "Start FullScreen?",MB_YESNO|MB_ICONQUESTION)==IDNO)
    {
        fullscreen=FALSE;                            // Windowed Mode
    }

    // Create Our OpenGL Window
    if (!CreateGLWindow("Tom Stanis & NeHe's Blending Tutorial",640,480,16,fullscreen))
    {
        return 0;                                    // Quit If Window Was Not Created
    }

    while(!done)                                    // Loop That Runs While done=FALSE
    {
        if (PeekMessage(&msg,NULL,0,0,PM_REMOVE))    // Is There A Message Waiting?
        {
            if (msg.message==WM_QUIT)                // Have We Received A Quit Message?
            {
                done=TRUE;                            // If So done=TRUE
            }
            else                                    // If Not, Deal With Window Messages
            {
                TranslateMessage(&msg);                // Translate The Message
                DispatchMessage(&msg);                // Dispatch The Message
            }
        }
        else                                        // If There Are No Messages
        {
            // Draw The Scene.  Watch For ESC Key And Quit Messages From DrawGLScene()
            if ((active && !DrawGLScene()) || keys[VK_ESCAPE])    // Active?  Was There A Quit Received?
            {
                done=TRUE;                            // ESC or DrawGLScene Signalled A Quit
            }
            else                                    // Not Time To Quit, Update Screen
            {
                SwapBuffers(hDC);                    // Swap Buffers (Double Buffering)
                if (keys['L'] && !lp)
                {
                    lp=TRUE;
                    light=!light;
                    if (!light)
                    {
                        glDisable(GL_LIGHTING);
                    }
                    else
                    {
                        glEnable(GL_LIGHTING);
                    }
                }
                if (!keys['L'])
                {
                    lp=FALSE;
                }
                if (keys['F'] && !fp)
                {
                    fp=TRUE;
                    filter+=1;
                    if (filter>2)
                    {
                        filter=0;
                    }
                }
                if (!keys['F'])
                {
                    fp=FALSE;
                }
                if (keys[VK_PRIOR])
                {
                    z-=0.02f;
                }
                if (keys[VK_NEXT])
                {
                    z+=0.02f;
                }
                if (keys[VK_UP])
                {
                    xspeed-=0.01f;
                }
                if (keys[VK_DOWN])
                {
                    xspeed+=0.01f;
                }
                if (keys[VK_RIGHT])
                {
                    yspeed+=0.01f;
                }
                if (keys[VK_LEFT])
                {
                    yspeed-=0.01f;
                }
                // Blending Code Starts Here
                if (keys['B'] && !bp)
                {
                    bp=TRUE;
                    blend = !blend;
                    if(blend)
                    {
                        glEnable(GL_BLEND);            // Turn Blending On
                        glDisable(GL_DEPTH_TEST);    // Turn Depth Testing Off
                    }
                    else
                    {
                        glDisable(GL_BLEND);        // Turn Blending Off
                        glEnable(GL_DEPTH_TEST);    // Turn Depth Testing On
                    }
                }
                if (!keys['B'])
                {
                    bp=FALSE;
                }
                // Blending Code Ends Here

                if (keys[VK_F1])                        // Is F1 Being Pressed?
                {
                    keys[VK_F1]=FALSE;                    // If So Make Key FALSE
                    KillGLWindow();                        // Kill Our Current Window
                    fullscreen=!fullscreen;                // Toggle Fullscreen / Windowed Mode
                    // Recreate Our OpenGL Window
                    if (!CreateGLWindow("Tom Stanis & NeHe's Blending Tutorial",640,480,16,fullscreen))
                    {
                        return 0;                        // Quit If Window Was Not Created
                    }
                }
            }
        }
    }

    // Shutdown
    KillGLWindow();                                    // Kill The Window
    return (msg.wParam);                            // Exit The Program
}