用mfc框架基于OpenGL实现雪花飞舞场景的源代码

以下基于MFC框架和OpenGL实现雪花飞舞场景的源代码：

首先是头文件和全局变量的声明：

#include <afxwin.h>
#include <gl\gl.h>
#include <gl\glu.h>

#define MAX_SNOWFLAKES 2000

struct Snowflake {
    float x, y, z;
    float speed;
    float angle;
};

Snowflake snowflakes[MAX_SNOWFLAKES];

float snowflakeSize = 0.02f;
float windSpeed = 0.01f;
float gravity = 0.0001f;

GLuint snowTexture;

BOOL SetupPixelFormat(HDC hDC);
void InitializeSnowflakes();
void DrawSnowflakes();
void UpdateSnowflakes();
void LoadSnowTexture();
void FreeSnowTexture();

class COpenGLWnd : public CFrameWnd {
public:
    COpenGLWnd();
    virtual ~COpenGLWnd();

protected:
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);
    afx_msg void OnPaint();
    afx_msg void OnSize(UINT nType, int cx, int cy);
    afx_msg void OnTimer(UINT_PTR nIDEvent);
    afx_msg void OnDestroy();

    DECLARE_MESSAGE_MAP()

private:
    HDC m_hDC;
    HGLRC m_hGLContext;
    int m_width, m_height;
};

COpenGLWnd::COpenGLWnd() {
    m_hDC = NULL;
    m_hGLContext = NULL;
}

COpenGLWnd::~COpenGLWnd() {
    if (m_hGLContext) {
        wglMakeCurrent(NULL, NULL);
        wglDeleteContext(m_hGLContext);
    }
}

BEGIN_MESSAGE_MAP(COpenGLWnd, CFrameWnd)
    ON_WM_CREATE()
    ON_WM_PAINT()
    ON_WM_SIZE()
    ON_WM_TIMER()
    ON_WM_DESTROY()
END_MESSAGE_MAP()

int COpenGLWnd::OnCreate(LPCREATESTRUCT lpCreateStruct) {
    if (CFrameWnd::OnCreate(lpCreateStruct) == -1) {
        return -1;
    }

    m_hDC = GetDC()->m_hDC;

    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,
        PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA,
        16,
        0, 0, 0, 0, 0, 0,
        0,
        0,
        0,
        0, 0, 0, 0,
        16,
        0,
        0,
        PFD_MAIN_PLANE,
        0,
        0, 0, 0
    };

    int pixelFormat = ChoosePixelFormat(m_hDC, &pfd);

    if (!SetupPixelFormat(m_hDC)) {
        MessageBox(_T("Could not setup pixel format."));
        return -1;
    }

    m_hGLContext = wglCreateContext(m_hDC);

    if (!wglMakeCurrent(m_hDC, m_hGLContext)) {
        MessageBox(_T("Could not make rendering context current."));
        return -1;
    }

    glEnable(GL_TEXTURE_2D);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClearDepth(1.0f);
    glDepthFunc(GL_LEQUAL);
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

    LoadSnowTexture();

    InitializeSnowflakes();

    SetTimer(1, 30, NULL);

    return 0;
}

void COpenGLWnd::OnPaint() {
    CPaintDC dc(this);
    SwapBuffers(m_hDC);
}

void COpenGLWnd::OnSize(UINT nType, int cx, int cy) {
    m_width = cx;
    m_height = cy;

    glViewport(0, 0, cx, cy);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, (GLfloat)cx / (GLfloat)cy, 0.1f, 100.0f);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void COpenGLWnd::OnTimer(UINT_PTR nIDEvent) {
    UpdateSnowflakes();
    Invalidate(FALSE);
}

void COpenGLWnd::OnDestroy() {
    if (snowTexture) {
        FreeSnowTexture();
    }

    CFrameWnd::OnDestroy();
}

BOOL SetupPixelFormat(HDC hDC) {
    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,
        PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA,
        16,
        0, 0, 0, 0, 0, 0,
        0,
        0,
        0,
        0, 0, 0, 0,
        16,
        0,
        0,
        PFD_MAIN_PLANE,
        0,
        0, 0, 0
    };

    int pixelFormat = ChoosePixelFormat(hDC, &pfd);

    if (pixelFormat == 0) {
        return FALSE;
    }

    if (!SetPixelFormat(hDC, pixelFormat, &pfd)) {
        return FALSE;
    }

    return TRUE;
}

void InitializeSnowflakes() {
    for (int i = 0; i < MAX_SNOWFLAKES; i++) {
        Snowflake& s = snowflakes[i];

        s.x = (float)(rand() % 1000) / 1000.0f - 0.5f;
        s.y = (float)(rand() % 1000) / 1000.0f - 0.5f;
        s.z = (float)(rand() % 1000) / 1000.0f * 5.0f;

        s.speed = (float)(rand() % 1000) / 10000.0f + 0.001f;
        s.angle = (float)(rand() % 360);
    }
}

void DrawSnowflakes() {
    glBindTexture(GL_TEXTURE_2D, snowTexture);

    glBegin(GL_QUADS);

    for (int i = 0; i < MAX_SNOWFLAKES; i++) {
        Snowflake& s = snowflakes[i];

        float x = s.x;
        float y = s.y;
        float z = s.z;

        float size = snowflakeSize * (1.0f - (z / 5.0f));

        glTexCoord2f(0.0f, 0.0f);
        glVertex3f(x - size, y - size, z);

        glTexCoord2f(1.0f, 0.0f);
        glVertex3f(x + size, y - size, z);

        glTexCoord2f(1.0f, 1.0f);
        glVertex3f(x + size, y + size, z);

        glTexCoord2f(0.0f, 1.0f);
        glVertex3f(x - size, y + size, z);
    }

    glEnd();
}

void UpdateSnowflakes() {
    for (int i = 0; i < MAX_SNOWFLAKES; i++) {
        Snowflake& s = snowflakes[i];

        s.x += windSpeed;
        s.y -= s.speed;
        s.z -= gravity;

        if (s.z < 0.0f) {
            s.z = 5.0f;
            s.speed = (float)(rand() % 1000) / 10000.0f + 0.001f;
            s.angle = (float)(rand() % 360);
        }
    }
}

void LoadSnowTexture() {
    CImage image;
    image.Load(_T("snow.bmp"));

    glGenTextures(1, &snowTexture);
    glBindTexture(GL_TEXTURE_2D, snowTexture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, image.GetWidth(), image.GetHeight(),
        0, GL_BGR_EXT, GL_UNSIGNED_BYTE, image.GetBits());
}

void FreeSnowTexture() {
    glDeleteTextures(1, &snowTexture);
}

class COpenGLApp : public CWinApp {
public:
    COpenGLApp();
    virtual ~COpenGLApp();

    virtual BOOL InitInstance();

private:
    COpenGLWnd m_mainWnd;
};

COpenGLApp::COpenGLApp() {
}

COpenGLApp::~COpenGLApp() {
}

BOOL COpenGLApp::InitInstance() {
    m_mainWnd.Create(NULL, _T("OpenGL Snow Scene"), WS_OVERLAPPEDWINDOW, CRect(0, 0, 640, 480));

    m_pMainWnd = &m_mainWnd;

    m_mainWnd.ShowWindow(SW_SHOW);
    m_mainWnd.UpdateWindow();

    return TRUE;
}

COpenGLApp theApp;

在头文件中，我们声明了 `Snowflake` 结构体，它包含雪花的位置、速度和角度。我们同时声明了一些全局变量，如雪花的大小、风向和重力。

`SetupPixelFormat` 函数设置了像素格式，创建了一个 OpenGL 上下文。`InitializeSnowflakes` 函数初始化了雪花的位置、速度和角度。`DrawSnowflakes` 函数绘制了所有的雪花。`UpdateSnowflakes` 函数更新雪花的位置。

`LoadSnowTexture` 函数加载了雪花纹理，`FreeSnowTexture` 函数释放了纹理。

`COpenGLWnd` 类继承自 `CFrameWnd`，它实现了 `OnCreate`、`OnPaint`、`OnSize`、`OnTimer` 和 `OnDestroy` 函数。在 `OnCreate` 函数中，我们创建了 OpenGL 上下文，并初始化了雪花和纹理。在 `OnPaint` 函数中，我们调用了 `SwapBuffers` 函数切换缓冲区。在 `OnSize` 函数中，我们设置了视口，并将投影矩阵设置为透视投影。在 `OnTimer` 函数中，我们更新雪花位置，并调用 `Invalidate` 函数更新窗口。在 `OnDestroy` 函数中，我们释放了纹理。

最后，在 `COpenGLApp` 类中，我们创建了 `COpenGLWnd` 对象，并将其显示出来。

注意：以上代码是在 Visual Studio 2019 中编写的，使用 MFC 应用程序模板创建，使用的是 OpenGL 版本是 1.1。如果需要使用更高版本的 OpenGL，需要修改代码。