project2.dpr

屏幕雪花

program Snow;

uses
  Windows,
  Messages;

const
    SnowNumber = 500; // 雪点数量-1

type
    SnowNode = record
      Point: TPoint;    // 雪点位置
      Color: Integer; // 先前颜色
      Speed: Integer; // 下落速率
      nMove: Integer; // 下落距离
      Stick: Integer; // '粘连'度
    end;

var
    SnowNodes: array[0..SnowNumber] of SnowNode; // 雪点数组
    hTimer: Integer; // '随机风向'时钟句柄
    CrWind: Integer; // 当前'风向' ( -1 ~ 1 )
    CrStep: Integer; // 当前循环步数(用于限速) 
    ScreenWidth, ScreenHeight: Integer; // 屏幕尺寸


    // 取屏幕尺寸 -> ScreenWidth, ScreenHeight
procedure GetScreenSize;
begin
    ScreenWidth := GetSystemMetrics(SM_CXSCREEN);
    ScreenHeight := GetSystemMetrics(SM_CYSCREEN);
end;

    // '随机风向'时钟
procedure TimerProc(hWnd: HWND; uMsg: UINT; idEvent: UINT; dwTime: DWORD); stdcall;
begin
    SetTimer(0, hTimer, (Random(27)+4) * 500, @TimerProc); // 重设下次风向改变时间
    if (CrWind <> 0) then CrWind := 0 else CrWind := Random(3) - 1; // 修改风向
end;

    // 初始化雪点数组
procedure InitSnowNodes;
var
    hScreenDc, J: Integer;
begin
    hScreenDc := CreateDC('DISPLAY', nil, nil, nil);
    for J := 0 to SnowNumber do
    begin
      SnowNodes[J].Point.X := Random(ScreenWidth);
      SnowNodes[J].Point.Y := Random(ScreenHeight);
      SnowNodes[J].Color := GetPixel(hScreenDc, SnowNodes[J].Point.X, SnowNodes[J].Point.Y);
      SnowNodes[J].Speed := Random(5) + 1; // 几次循环作下落一次 (1~5)
      SnowNodes[J].nMove := Random(SnowNodes[J].Speed)+1; // 每次下落距离(1~5)
      SnowNodes[J].Stick := 30 - Random(SnowNodes[J].Speed); // '粘连'度(几次循环作一次粘连判断)
    end;
    DeleteDC(hScreenDc);
end;

    // 移动雪点 ..
procedure MoveSnowNodes;
var
    hScreenDc, I, X, Y: Integer;
begin
    hScreenDc := CreateDC('DISPLAY', nil, nil, nil);
    for I := 0 to SnowNumber do
    begin
     // 控制雪点下降速率
      if (CrStep mod SnowNodes[I].Speed) <> 0 then Continue;
     // 恢复上次被覆盖点
      if GetPixel(hScreenDc, SnowNodes[I].Point.X, SnowNodes[I].Point.Y) = $FFFFFF then
        SetPixel(hScreenDc, SnowNodes[I].Point.X, SnowNodes[I].Point.Y, SnowNodes[I].Color);
     // 根据风向作随机飘落
      X := SnowNodes[I].Point.X + Random(3) - 1 + CrWind;
      Y := SnowNodes[I].Point.Y + SnowNodes[I].nMove;
     // 积雪(停留)效果处理
      if ( (CrStep mod SnowNodes[I].Stick) = 0 ) // 降低积雪概率 ..
         and ( GetPixel(hScreenDc, X, Y) <> GetPixel(hScreenDc, X, Y+1) ) // '边缘'判断
         and ( GetPixel(hScreenDc, X-1, Y) <> GetPixel(hScreenDc, X-1, Y+1) )
         and ( GetPixel(hScreenDc, X+1, Y) <> GetPixel(hScreenDc, X+1, Y+1) ) then
      begin
       // 稍微调整坐标
        if GetPixel(hScreenDc, X, Y-1) = GetPixel(hScreenDc, X, Y-2) then Dec(Y) // 上边缘
        else if GetPixel(hScreenDc, X, Y+1) = GetPixel(hScreenDc, X, Y+2) then Inc(Y); // 下边缘
        Inc(X, CrWind);
       // 画三个点(雪花)
        SetPixel(hScreenDc, X, Y, $FFFFFF);
        SetPixel(hScreenDc, X+1, Y+1, $FFFFFF);
        SetPixel(hScreenDc, X-1, Y+1, $FFFFFF);
       // 重生雪点
        SnowNodes[I].Point.Y := Random(10);
        SnowNodes[I].Point.X := Random(ScreenWidth);
        SnowNodes[I].Color := GetPixel(hScreenDc, SnowNodes[I].Point.X, SnowNodes[I].Point.Y);
      end else
      begin
        if (X < 0) or (X > ScreenWidth) or (Y > ScreenHeight) then // 超出范围则重生雪点
        begin
          SnowNodes[I].Point.Y := Random(10);
          SnowNodes[I].Point.X := Random(ScreenWidth);
          SnowNodes[I].Color := GetPixel(hScreenDc, SnowNodes[I].Point.X, SnowNodes[I].Point.Y);
        end else
        begin
         // 保存颜色并绘制雪点
          SnowNodes[I].Color := GetPixel(hScreenDc, X, Y);
          SetPixel(hScreenDc, X, Y, $FFFFFF);
         // 此时保存新雪点位置
          SnowNodes[I].Point.X := X;
          SnowNodes[I].Point.Y := Y;
        end;
      end;
    end;
    DeleteDC(hScreenDc);
    Inc(CrStep);
end; 

var
    ThreadMsg: TMsg;    // 标准消息结构体
    Frequency: Int64; // 高性能定时器频率
    StartCt, EndCt: Int64; // 高性能定时器计数
    ElapsedTime: Extended; // 时间间隔
begin
    Randomize;    GetScreenSize;    InitSnowNodes; // 初始化
    QueryPerformanceFrequency(Frequency); // 高性能定时器频率
    hTimer := SetTimer(0, 0, Random(5)*500, @TimerProc); // 安装随机风向定时器
    RegisterHotKey(0, 0, MOD_ALT, orD('S')); // 注册退出热键 ALT+S
    while TRUE do // 消息循环
    begin
      QueryPerformanceCounter(StartCt); // 执行运算前 计数值
      if PeekMessage(ThreadMsg, 0, 0, 0, PM_REMOVE) then // 取到消息
      begin
        case ThreadMsg.message of
          WM_TIMER:
            TimerProc(0, 0, 0, 0); // 预设风向改变时间已到

          WM_HOTKEY:
            begin
              KillTimer(0, hTimer); // 删除随机风向定时器
              UnregisterHotKey(0, 0); // 删除退出热键 Ctrl+L
              InvalidateRect(0, nil, TRUE); // 刷新屏幕
              Break; // 跳出消息循环
            end;

          WM_DISPLAYCHANGE:
            begin
              GetScreenSize; // 重新取屏幕尺寸
              InitSnowNodes; // 初始化雪点数组
            end;
        end;
      end;
      MoveSnowNodes; // 移动雪点
      QueryPerformanceCounter(EndCt); // 执行运算后计数值
      ElapsedTime := (EndCt-StartCt)/Frequency; 
      if (ElapsedTime < 0.0005) then Sleep(2) // 简单限速
      else if (ElapsedTime < 0.0010) then Sleep(1)
           else if (ElapsedTime < 0.0015) then Sleep(0);
    end;
end.