桌面雪花

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win32程序，可以在桌面上下雪的，很好很强大的效果，代码如下：

#include <windows.h>
#include <math.h>
#include <stdlib.h>
#define ID_TIMER    1
#define SNOWNUM      500 // 雪花数量
#define CONTRAST    50    // 对比度
#define YSTART      5    // 用于确定雪花初始时的y坐标
#define SNOWCR      RGB(0xFF, 0xFF, 0xFF) //雪花的颜色—白色
#define SNOWGATHERCR RGB(0xDB, 0xDB, 0xFF) //堆积雪花的颜色

typedef struct tagSnow
{
POINT ptSnowsPos[SNOWNUM]; //用于保存各个雪花的坐标
COLORREF crOrg[SNOWNUM]; //用于画雪花前屏幕原来的颜色
int iVx, iVy, iAllVx, iAllVy;
}Snow;

void initSnow(HDC hdc, Snow *sn, int iSnow, int cxScreen);
int GetContrast(HDC hdc, Snow *sn, int iSnow);
void drawSnow(HDC hdc, Snow *sn, int cxScreen);

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
        static TCHAR szAppName[] = TEXT ("clsDeskSnow") ;
        HWND            hwnd ;
        MSG            msg ;
        WNDCLASS    wndclass ;

        wndclass.style        = CS_HREDRAW | CS_VREDRAW ;
        wndclass.lpfnWndProc = WndProc ;
        wndclass.cbClsExtra    = 0 ;
        wndclass.cbWndExtra    = 0 ;
        wndclass.hInstance    = hInstance ;
        wndclass.hIcon        = LoadIcon (NULL, IDI_APPLICATION) ;
        wndclass.hCursor      = LoadCursor (NULL, IDC_ARROW) ;
        wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
        wndclass.lpszMenuName = NULL ;
        wndclass.lpszClassName = szAppName ;

        if(!RegisterClass (&wndclass))
        {
            MessageBox (NULL, TEXT ("This program requires Windows NT!"), szAppName, MB_ICONERROR) ;
            return 0;
        }

        hwnd = CreateWindow (szAppName,        TEXT ("桌面下雪"),
                            WS_MINIMIZEBOX | WS_SYSMENU,
                            CW_USEDEFAULT, CW_USEDEFAULT,
                            240, 120,
                            NULL, NULL, hInstance, NULL) ;

        ShowWindow (hwnd, iCmdShow) ;
        UpdateWindow (hwnd) ;

        while (GetMessage (&msg, NULL, 0, 0))
        {
            TranslateMessage (&msg) ;
            DispatchMessage (&msg) ;
        }
        return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
      HDC          hdc ;
      PAINTSTRUCT ps ;
      RECT        rect ;
      static int cxScreen, cyScreen; //屏幕宽高度(单位:像素)
      static int iTimes, iLoopTimes=100;
      static Snow snowDream;
      int i;

      switch (message)
      {
        case WM_CREATE:
            cxScreen = GetSystemMetrics (SM_CXSCREEN) ;
            cyScreen = GetSystemMetrics (SM_CYSCREEN) ;
            srand ((int) GetCurrentTime ()) ; //初始化随机数发生器
            snowDream.iAllVx = (unsigned)rand()%3 - 1; //雪花总体水平飘行速度(-1,0,1)
            snowDream.iAllVy = (unsigned)rand()%2 + 1; //雪花总体垂直下落速度(1,2)
            hdc = GetDC(NULL); //检索整个屏幕的设备上下文环境
            for(i=0; i <SNOWNUM; i++)
            {
                snowDream.ptSnowsPos[i].x = rand() % cxScreen; //一个雪花开始下落的x坐标
                snowDream.ptSnowsPos[i].y = rand() % YSTART; //一个雪花开始下落的y坐标
                snowDream.crOrg[i] = GetPixel(hdc, snowDream.ptSnowsPos[i].x,
                          snowDream.ptSnowsPos[i].y); //获取给定点的原来的颜色值
            }
            ReleaseDC(NULL, hdc);
            SetTimer(hwnd, ID_TIMER, 10, NULL); //定时器，10毫秒
            return 0 ;

        case WM_DISPLAYCHANGE: //当显示分辨率改变的时候
            cxScreen = GetSystemMetrics (SM_CXSCREEN) ;
            cyScreen = GetSystemMetrics (SM_CYSCREEN) ;
            return 0;

        case WM_TIMER:
            hdc = GetDC(NULL); //检索整个屏幕的设备上下文环境
            if(iTimes > iLoopTimes)
            {
                iTimes = 0;
                iLoopTimes = 50 + (unsigned)rand();
                if(snowDream.iAllVx != 0)
                  snowDream.iAllVx = 0;
                else
                  snowDream.iAllVx = (unsigned)rand()%3 - 1; //雪花总体水平飘行速度(-1,0,1)
                snowDream.iAllVy = (unsigned)rand()%2 + 1; //雪花总体垂直下落速度(1,2)
            }
            else
                iTimes++;
            drawSnow(hdc, &snowDream, cxScreen);
            ReleaseDC(NULL, hdc);
            return 0;

        case WM_PAINT:
            hdc = BeginPaint (hwnd, &ps) ;
            GetClientRect (hwnd, &rect) ;
            DrawText (hdc, TEXT ("桌面下雪!"), -1, &rect,
                      DT_SINGLELINE | DT_CENTER | DT_VCENTER) ;
            EndPaint (hwnd, &ps) ;
            return 0 ;

        case WM_DESTROY:
            KillTimer(hwnd, ID_TIMER); // 中止定时器
            InvalidateRect(NULL, NULL, TRUE); // 刷新桌面
            PostQuitMessage (0) ;
            return 0 ;
        }
        return DefWindowProc (hwnd, message, wParam, lParam) ;
}

void initSnow(HDC hdc, Snow *sn, int iSnow, int cxScreen) //初始化第iSnow个雪花
{
sn->ptSnowsPos[iSnow].x = (unsigned)rand() % cxScreen; //x范围整个屏幕宽
sn->ptSnowsPos[iSnow].y = (unsigned)rand() % YSTART; //y范围离屏幕顶部YSTART像素点以内
sn->crOrg[iSnow] = GetPixel(hdc, sn->ptSnowsPos[iSnow].x,
            sn->ptSnowsPos[iSnow].y ) ;//获取给定点的原来的颜色值
}

int GetContrast(HDC hdc, Snow *sn, int iSnow)
{
int iR, iG, iB;
COLORREF crCmp;

if(0 == sn->iVx) //若水平速度为0，则取比其大一个像素的正下方的点
    crCmp = GetPixel(hdc, sn->ptSnowsPos[iSnow].x, sn->ptSnowsPos[iSnow].y + 1);
else //若水平速度>0，取右下方的点。 <0则取左下方的点
    crCmp = GetPixel(hdc, sn->ptSnowsPos[iSnow].x + (sn->iVx>0?1:-1), sn->ptSnowsPos[iSnow].y + 1);

if(crCmp==SNOWCR) //如果为雪花的颜色
    return 0;

//分别获取crCmp与对比点的蓝、绿、红部分的差值
iB = abs((crCmp>>16)&0xFF - (sn->crOrg[iSnow]>>16)&0xFF);
iG = abs((crCmp>>8)&0xFF - (sn->crOrg[iSnow]>>8)&0xFF);
iR = abs((crCmp)&0xFF    - (sn->crOrg[iSnow])&0xFF);

return (iR+iG+iB)/3;
}

void drawSnow(HDC hdc, Snow *sn, int cxScreen)
{
int i;
for(i=0; i <SNOWNUM; i++)
{
      //如果保存的原来的颜色不是雪花的颜色
      if(sn->crOrg[i] != SNOWCR)
        SetPixel(hdc, sn->ptSnowsPos[i].x, sn->ptSnowsPos[i].y,
          sn->crOrg[i]); //还原上一个位置的颜色

      sn->iVx = sn->iAllVx*(i%3+1); //雪花的x飘动速度
      sn->iVy = sn->iAllVy*(i%3+1); //雪花的y飘动速度
      //rand()%5-2使雪花下落的时候有抖动效果
      sn->ptSnowsPos[i].x += sn->iVx+rand()%5-2; //雪花的下一个x坐标
      sn->ptSnowsPos[i].y += sn->iVy+1; //雪花的下一个y坐标

      //获取给定点的原来的颜色值
      sn->crOrg[i] = GetPixel(hdc, sn->ptSnowsPos[i].x, sn->ptSnowsPos[i].y);

      if(CLR_INVALID == sn->crOrg[i]) //如果获取颜色失败,即雪花飘出了屏幕
      {
        initSnow(hdc, sn, i, cxScreen); //重新初始化雪花
        continue;
      }
      if(sn->crOrg[i] != SNOWCR) //若当前点的颜色不等于雪花的颜色
      {
        if(SNOWGATHERCR == sn->crOrg[i]) //当前点的颜色=堆积的雪的颜色
      { //设置为雪花的颜色
          SetPixel(hdc, sn->ptSnowsPos[i].x, sn->ptSnowsPos[i].y, SNOWCR);
          sn->crOrg[i] = SNOWCR;
          //initSnow(hdc, sn, i, cxScreen); //重新初始化雪花
      }
      else if(GetContrast(hdc, sn, i) > 50) //若对比度>50
        { //堆积雪花
            SetPixel(hdc, sn->ptSnowsPos[i].x, sn->ptSnowsPos[i].y, SNOWGATHERCR);
            SetPixel(hdc, sn->ptSnowsPos[i].x-1, sn->ptSnowsPos[i].y+1, SNOWGATHERCR);
            SetPixel(hdc, sn->ptSnowsPos[i].x+1, sn->ptSnowsPos[i].y+1, SNOWGATHERCR);
            initSnow(hdc, sn, i, cxScreen); //重新初始化雪花
        }
        else //对比度 <50,不堆积,画出这帧雪花.等下次的时候再还原此点原本的颜色.以产生飘动效果
          SetPixel(hdc, sn->ptSnowsPos[i].x, sn->ptSnowsPos[i].y, SNOWCR);
      }
}
}
by:yz

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