深入SetOP2函数

SetROP2函数：设置前景绘制模式，当前绘制的像素值是当前屏幕像素值的反，这样可以擦出上一次绘制的结果：

模仿 《windows程序设计》第七章BLOCKOUT程序：

code：

#include <windows.h>

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

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd )
{
    static TCHAR szAppName[] = TEXT ("BlokOut1") ;
    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 ("Program requires Windows NT!"),
            szAppName, MB_ICONERROR) ;
        return 0 ;
    }

    hwnd = CreateWindow (szAppName, TEXT ("Mouse Button Demo"),
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hInstance, NULL) ;

    ShowWindow (hwnd, SW_SHOWNORMAL) ;
    UpdateWindow (hwnd) ;

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

void Draw(HWND hwnd,POINT ptbeg,POINT ptend)
{
    HDC hdc;
    hdc=GetDC(hwnd);
    SetROP2(hdc,R2_NOT);//可以把这行注释掉，看看结果
    SelectObject(hdc,GetStockObject(NULL_BRUSH));
    Rectangle(hdc,ptbeg.x,ptbeg.y,ptend.x,ptend.y);
    ReleaseDC(hwnd,hdc);
}

LRESULT CALLBACK wndproc(HWND hwnd,UINT message,WPARAM wparam,LPARAM lparam)
{
    static POINT ptbeg,ptend,Boxbeg,Boxend;
    static BOOL  flag1,flag2;
    HDC          hdc;
    PAINTSTRUCT ps;
    switch(message)
    {
    case WM_LBUTTONDOWN:
        ptbeg.x=ptend.x=LOWORD(lparam);
        ptbeg.y=ptend.y=HIWORD(lparam);

        Draw(hwnd,ptbeg,ptend);
        flag1=TRUE;
        SetCursor(LoadCursor(NULL,IDC_CROSS));

        return 0;
    case WM_MOUSEMOVE:
        if (flag1)
        {
            SetCursor(LoadCursor(NULL,IDC_CROSS));
            Draw(hwnd,ptbeg,ptend);
            ptend.x=LOWORD(lparam);
            ptend.y=HIWORD(lparam);
            Draw(hwnd,ptbeg,ptend);
        }
        return 0;
    case WM_LBUTTONUP:
        if (flag1)
        {
            SetCursor(LoadCursor(NULL,IDC_ARROW));
            Draw(hwnd,ptbeg,ptend);
            Boxbeg=ptbeg;
            Boxend.x=LOWORD(lparam);
            Boxend.y=HIWORD(lparam);
            flag1=FALSE;
            flag2=TRUE;
            InvalidateRect(hwnd,NULL,TRUE);
        }
        return 0;
    case WM_PAINT:
        if (flag2)
        {   hdc=BeginPaint(hwnd,&ps);
            SelectObject(hdc,GetStockObject(BLACK_BRUSH));
            //Draw(hwnd,Boxbeg,Boxend);
            Rectangle(hdc,Boxbeg.x,Boxbeg.y,Boxend.x,Boxend.y);
            EndPaint(hwnd,&ps);
        }
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd,message,wparam,lparam);

 }