GetAsyncKeyState 功能的使用 判断上下左右键是否被按下或弹起

// DEMO3_12.CPP - GetAsynKeyState Demo

// INCLUDES //////////GetAsyncKeyState/////////////////////////////////////
#define WIN32_LEAN_AND_MEAN  // just say no to MFC

#include <windows.h>   // include all the windows headers
#include <windowsx.h>  // include useful macros
#include <mmsystem.h>  // very important and include WINMM.LIB too!
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

// DEFINES ////////////////////////////////////////////////

// defines for windows
#define WINDOW_CLASS_NAME "WINCLASS1"

// MACROS /////////////////////////////////////////////////

#define KEYDOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)
#define KEYUP(vk_code)   ((GetAsyncKeyState(vk_code) & 0x8000) ? 0 : 1)
/*
  0x8000二进制值是1000000000000000,两者进行与运算  
  即如果GetAsyncKeyState(vk_code)最高位是1,则取值1,  
  即此时KEYDOWN   后者正好相反
  函数GetAsyncKeyState确定在调用它时某个按键处于弹起还是按下的，以及此按键是否在上一次调用GetAsyncKeyState之后（“又”）按下过（重复也算按下）。
  这句话的完整意思是:预定义了一个KEYDOWN参数为vk_code 他的定义的含义是判断一个键是否被按下(GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0如果按下了就是1,没有按下就是0
  然后其它地方用的时候直接用KEYDOWN(vk_code)判断这个键是否按下,相反弹起来是1按下是0
*/

// GLOBALS ////////////////////////////////////////////////
HWND      main_window_handle = NULL; // globally track main window
HINSTANCE hinstance_app      = NULL; // globally track hinstance
char buffer[80];                     // general printing buffer

// FUNCTIONS //////////////////////////////////////////////
LRESULT CALLBACK WindowProc(HWND hwnd,
          UINT msg,
                            WPARAM wparam,
                            LPARAM lparam)
{
// this is the main message handler of the system
PAINTSTRUCT  ps;  // used in WM_PAINT
HDC    hdc; // handle to a device context
char buffer[80];        // used to print strings

// what is the message
switch(msg)
 { 
 case WM_CREATE:
        {
  // do initialization stuff here
        // return success
  return(0);
  } break;
  
 case WM_PAINT:
  {
  // simply validate the window
        hdc = BeginPaint(hwnd,&ps); 
       
        // end painting
        EndPaint(hwnd,&ps);

        // return success
  return(0);
     } break;

 case WM_DESTROY:
  {

  // kill the application, this sends a WM_QUIT message
  PostQuitMessage(0);

        // return success
  return(0);
  } break;

 default:break;

    } // end switch

// process any messages that we didn't take care of
return (DefWindowProc(hwnd, msg, wparam, lparam));

} // end WinProc

// WINMAIN ////////////////////////////////////////////////
int WINAPI WinMain( HINSTANCE hinstance,
     HINSTANCE hprevinstance,
     LPSTR lpcmdline,
     int ncmdshow)
{

WNDCLASSEX winclass; // this will hold the class we create
HWND    hwnd;  // generic window handle
MSG     msg;   // generic message
HDC        hdc;      // graphics device context

// first fill in the window class stucture
winclass.cbSize         = sizeof(WNDCLASSEX);
winclass.style   = CS_DBLCLKS | CS_OWNDC |
                          CS_HREDRAW | CS_VREDRAW;
winclass.lpfnWndProc = WindowProc;
winclass.cbClsExtra  = 0;
winclass.cbWndExtra  = 0;
winclass.hInstance  = hinstance;
winclass.hIcon   = LoadIcon(NULL, IDI_APPLICATION);
winclass.hCursor  = LoadCursor(NULL, IDC_ARROW);
winclass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
winclass.lpszMenuName = NULL;
winclass.lpszClassName = WINDOW_CLASS_NAME;
winclass.hIconSm        = LoadIcon(NULL, IDI_APPLICATION);

// save hinstance in global
hinstance_app = hinstance;

// register the window class
if (!RegisterClassEx(&winclass))
 return(0);

// create the window
if (!(hwnd = CreateWindowEx(NULL,                  // extended style
                            WINDOW_CLASS_NAME,     // class
          "GetAsyncKeyState() Demo", // title
          WS_OVERLAPPEDWINDOW | WS_VISIBLE,
           0,0,   // initial x,y
          400,300,  // initial width, height
          NULL,   // handle to parent
          NULL,   // handle to menu
          hinstance,// instance of this application
          NULL))) // extra creation parms
return(0);

// save main window handle
main_window_handle = hwnd;

// enter main event loop, but this time we use PeekMessage()
// instead of GetMessage() to retrieve messages
while(TRUE)
 {
    // test if there is a message in queue, if so get it
 if (PeekMessage(&msg,NULL,0,0,PM_REMOVE))
    {
    // test if this is a quit
       if (msg.message == WM_QUIT)
           break;
 
    // translate any accelerator keys
    TranslateMessage(&msg);

    // send the message to the window proc
    DispatchMessage(&msg);
    } // end if
   
       // main game processing goes here
 
       // get a graphics context
       hdc = GetDC(hwnd);

       // set the foreground color to green
       SetTextColor(hdc, RGB(0,255,0));
        
       // set the background color to black
       SetBkColor(hdc, RGB(0,0,0));
        
       // set the transparency mode to OPAQUE
       SetBkMode(hdc, OPAQUE);

       // print out the state of each arrow key
       sprintf(buffer,"Up Arrow: = %d   ",KEYDOWN(VK_UP));
       TextOut(hdc, 0,0, buffer, strlen(buffer));

       sprintf(buffer,"Down Arrow: = %d   ",KEYDOWN(VK_DOWN));
       TextOut(hdc, 0,16, buffer, strlen(buffer));

       sprintf(buffer,"Right Arrow: = %d   ",KEYDOWN(VK_RIGHT));
       TextOut(hdc, 0,32, buffer, strlen(buffer));

       sprintf(buffer,"Left Arrow: = %d   ",KEYDOWN(VK_LEFT));
       TextOut(hdc, 0,48, buffer, strlen(buffer));

       // release the dc back
       ReleaseDC(hwnd, hdc);

 } // end while

// return to Windows like this
return(msg.wParam);

} // end WinMain

///////////////////////////////////////////////////////////