OpenGL入门笔记（六）

其实纹理滤波是什么概念我也还不了解，图形学就是这样，理论和实践都不可偏废，可究竟从何处入手也是个两难的问题，有人说“图形血到最后就是数学”，对我这样的新手来说，快速有个概念也许不失为一个笨办法吧。

 

Nehe在第6课里已经用了线性滤波了，并且还推荐我们把gl_nearest（不光滑）滤波方式和线性滤波结合起来使用，在近处时用线性滤波，在远处时用gl_nearest（不光滑）滤波，因为线性滤波对运行机器的要求高些。

Demo7
#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 ( NEW )
bool    lp;                    // L Pressed? ( NEW )
bool    fp;                    // F 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/Crate.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
    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("NeHe's Textures, Lighting & Keyboard 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;
                }

                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("NeHe's Textures, Lighting & Keyboard Tutorial",640,480,16,fullscreen))
                    {
                        return 0;                        // Quit If Window Was Not Created
                    }
                }
            }
        }
    }

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

 

这一课里还讲解了如何使用光照。他使用了两种不同的光。第一种称为环境光。环境光来自于四面八方。所有场景中的对象都处于环境光的照射中。第二种类型的光源叫做漫射光。漫射光由特定的光源产生，并在您的场景中的对象表面上产生反射。处于漫射光直接照射下的任何对象表面都变得很亮，而几乎未被照射到的区域就显得要暗一些。创建光源的过程和颜色的创建完全一致，先设置用来创建光源的数组。前三个参数分别是RGB三色分量，最后一个是alpha通道参数。

 

GLfloat LightAmbient[]= { 0.5f, 0.5f, 0.5f, 1.0f };　　　　 // 环境光参数

GLfloat LightDiffuse[]= { 1.0f, 1.0f, 1.0f, 1.0f }; 　　　　// 漫射光参数

 

最后保存光源的位置。前三个参数和glTranslate中的一样。依次分别是XYZ轴上的位移。最后一个参数取为1.0f。这将告诉OpenGL这里指定的坐标就是光源的位置。

 

GLfloat LightPosition[]= { 0.0f, 0.0f, 2.0f, 1.0f };　　　　// 光源位置

 

教程里使用三种纹理滤波方式，第一种纹理（texture 0）使用gl_nearest（不光滑）滤波方式构建。第二种纹理（texture 1）使用gl_linear（线性滤波）方式，离屏幕越近的图像看起来就越光滑。第三种纹理 （texture 2）使用mipmapped滤波方式,这将创建一个外观十分优秀的纹理。

 

下面是创建纹理的新方法：Mip-mapping（纹理细化）。您可能会注意到当图像在屏幕上变得很小的时候，很多细节将会丢失。刚才还很不错的图案变得很难看。当您告诉OpenGL创建一个mipmapped的纹理后，OpenGL将尝试创建不同尺寸的高质量纹理。当您向屏幕绘制一个mipmapped纹理的时候，OpenGL将选择它已经创建的外观最佳的纹理（带有更多细节）来绘制，而不仅仅是缩放原先的图像（这将导致细节丢失）。

 

要绕过OpenGL对纹理宽度和高度所加的限制 （64、128、256等等）。办法就是 gluBuild2DMipmaps，我们可以使用任意的位图来创建纹理。OpenGL将自动将它缩放到正常的大小。

 

// 创建 MipMapped 纹理
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);

 

下面生成mipmapped纹理。我们使用三种颜色（红，绿，蓝）来生成一个2D纹理。TextureImage[0]->sizeX 是位图宽度，extureImage[0]->sizeY是位图高度，GL_RGB意味着我们依次使用RGB色彩。GL_UNSIGNED_BYTE意味着纹理数据的单位是字节。TextureImage[0]->data指向我们创建纹理所用的位图。

    gluBuild2DMipmaps(GL_TEXTURE_2D, 3,
    TextureImage[0]->sizeX, TextureImage[0]->sizeY,
    GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);　

 

现在开始设置光源。下面一行设置环境光的发光量，光源light1开始发光：

 

　 glLightfv(GL_LIGHT1, GL_AMBIENT, LightAmbient);　　// 设置环境光

设置漫射光的发光量：

glLightfv(GL_LIGHT1, GL_DIFFUSE, LightDiffuse);　　// 设置漫射光

然后设置光源的位置：

glLightfv(GL_LIGHT1, GL_POSITION,LightPosition);　 // 光源位置

 

最后，我们启用一号光源，没有启用GL_LIGHTING，所以您看不见任何光线（只对光源进行设置、定位、甚至启用，光源都不会工作。除非我们启用GL_LIGHTING）。

 

glEnable(GL_LIGHT1);　　　　　　　　　　　　　　　 // 启用一号光源

 

课程中还学习了一个新的函数glNormal3f。Normal就是法线的意思，所谓法线是指经过面（多边形）上的一点且垂直于这个面（多边形）的直线。使用光源的时候必须指定一条法线。法线告诉OpenGL这个多边形的朝向，并指明多边形的正面和背面。如果没有指定法线，什么怪事情都可能发生。