随机画出随机颜色的线hpen MoveToEx LineTo DeleteObject

// DEMO4_2.CPP  - Line drawing demo

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

#include    // include all the windows headers
#include   // include useful macros
#include   // very important and include WINMM.LIB too!
#include
#include
#include

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

// defines for windows
#define WINDOW_CLASS_NAME "WINCLASS1"

#define WINDOW_WIDTH  400
#define WINDOW_HEIGHT 300

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

#define KEYDOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)
#define KEYUP(vk_code)   ((GetAsyncKeyState(vk_code) & 0x8000) ? 0 : 1)

// 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
          "Line Drawing Demo", // title
          WS_OVERLAPPEDWINDOW | WS_VISIBLE,
           0,0,   // initial x,y
          WINDOW_WIDTH, // initial width
                            WINDOW_HEIGHT,// initial 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

       // draw a random line
   
       // get the graphics device context
       hdc = GetDC(hwnd);

       // create a random colored pen
       HPEN hpen = CreatePen(PS_SOLID,1,RGB(rand()%256,rand()%256,rand()%256));
       /*
    The CreatePen function creates a logical pen that has the specified style, width, and color.
    The pen can subsequently be selected into a device context and used to draw lines and curves.
    参数为：样式，宽度，颜色
       样式参考：ms-help://MS.MSDNQTR.v80.chs/MS.MSDN.v80/MS.WIN32COM.v10.en/gdi/pens_9wha.htm
    */
       // select the pen into context
       HPEN old_hpen = (HPEN)SelectObject(hdc,hpen);
       /*
    The SelectObject function selects an object into the specified device context (DC). The new object replaces the previous object of the same type.
    Return Values 返回老的画笔
    */
       // move to a random postion
       MoveToEx(hdc, rand()%WINDOW_WIDTH, rand()%WINDOW_HEIGHT, NULL);
    /*
    The MoveToEx function updates the current position to the specified point and optionally returns the previous position
    MoveToEx是用来移动当前画笔的位置，LineTo是用来画直线的函数，其实在计算机图形里的直线显示是使用光栅图形学里的原理
    */

       // draw a line
       LineTo(hdc,rand()%WINDOW_WIDTH, rand()%WINDOW_HEIGHT);
    //The LineTo function draws a line from the current position up to, but not including, the specified point.

       // now delete the pen
       SelectObject(hdc,old_hpen);
    //还原到原来的默认画笔
    //删除画笔
       DeleteObject(hpen);
   
       // release the device context
       ReleaseDC(hwnd,hdc);
    //翻译HDC

 
       // main game processing goes here
    if (KEYDOWN(VK_ESCAPE))
          SendMessage(hwnd, WM_CLOSE, 0,0);
      
 } // end while

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

} // end WinMain

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