Windows编程- hdc和hwnd的区别

hWnd是窗口句柄，其中包含窗口的属性。例如，窗口的大小，显示位置，父窗口。hDC(Handle to Device Context)是图像的设备描述表，窗口显示上下文句柄，其中可以进行图形显示。利用hDC=GetDC(hWnd)，可以获得一个窗口的图形设备描述表。可以通过ReleaseDC()函数释放。

下面的例子是获得图形设备表，并在窗口中打印text文本。 执行的结果，如下图。程序不停的执行main event loop 中绘制text部分。

 

// INCLUDES ///////////////////////////////////////////////
#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>

#include "GLres.h"

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

// defines for windows 
#define WINDOW_CLASS_NAME "WINCLASS1"

// GLOBALS ////////////////////////////////////////////////
HWND      main_window_handle = NULL; // globally track main window
HINSTANCE hinstance_app      = NULL; // globally track hinstance

// 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

// 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);     
        // you would do all your painting here
        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

// 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(hinstance, MAKEINTRESOURCE(ICON_GL));
winclass.hCursor        = LoadCursor(NULL, IDC_ARROW); 
winclass.hbrBackground    = (HBRUSH)GetStockObject(BLACK_BRUSH);
winclass.lpszMenuName    = NULL;
winclass.lpszClassName    = WINDOW_CLASS_NAME;
winclass.hIconSm        = LoadIcon(hinstance, MAKEINTRESOURCE(ICON_GL));

// 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
                            "GDI Text Printing Demo", // title
                            WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                             0,0,      // initial x,y
                            800,800,  // 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;

// get the dc and hold it
HDC hdc = GetDC(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
    
    // set the foreground color to random
    SetTextColor(hdc, RGB(rand()%256,rand()%256,rand()%256));

    // set the background color to black
    SetBkColor(hdc, RGB(0,0,0));

    // finally set the transparency mode to transparent
    SetBkMode(hdc, TRANSPARENT);

    // draw some text at a random location
    TextOut(hdc,rand()%800,rand()%800, "Green Light", strlen("Green Light"));

    Sleep(10);
    
    } // end while

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

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

} // end WinMain

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