unsigned char bybits[16]={0x55,0x0,0xaa,0x0,0x55,0x0,0xaa,0x0,
                          0x55,0x0,0xaa,0x0,0x55,0x0,0xaa,0x0};
HANDLE hBitmap,hBrush;

//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    /使屏幕暗下来
    HANDLE hdc5;
    hBitmap=CreateBitmap(8,8,1,1,&bybits[0]);
    hBrush=CreatePatternBrush(hBitmap);
    hdc5=GetDC(0);
    SelectObject(hdc5,hBrush);
    PatBlt(hdc5,0,0,Screen->Width,Screen->Height,0xa000c9);
    DeleteObject(hBrush);
    DeleteObject(hBitmap);
    ReleaseDC(0,hdc5);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button2Click(TObject *Sender)
{
    //复原屏幕
    InvalidateRect(0,0,1);
}
//---------------------------------------------------------------------------