高级GDI图形编程(3)

 高级GDI图形编程(3)
1.绘制圆
(1)事实上，GDI是按照绘制椭圆的方式来画圆。还有更独特的,实际上GDI先绘制一个有边界的矩形,GDI则绘制被这个举行包围的椭圆。本质上讲定义椭圆的原点的同时也在定义长轴和短轴。
(2)Ellipse()是绘制椭圆的函数
函数原型:BOOL Ellipse(HDC hdc,
                      int nLeftRect,
                      int nTopRect,
                      int nRightRect,
                      int nBottomRect)
因此，要画圆的话，必须首先确认有边界的矩形是正方形
例如：要绘制一个圆心为(20,20)半径为10的圆
Ellipse(hdc,10,10,30,30)

以下是一个小球飞来飞去的例子:
// DEMO4_4.CPP  - Ellipse Animation Demo

// 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>

// 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
          "Ellipse Animation 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;

// get the graphics device context once this time and keep it
// this is possible due to the CS_OWNDC flag
hdc = GetDC(hwnd);

// seed random number generator
srand(GetTickCount());

// create the pens and brushes
HPEN   white_pen = CreatePen(PS_SOLID, 1, RGB(255,255,255));
HPEN   black_pen = CreatePen(PS_SOLID, 1, RGB(0,0,0));
HBRUSH green_brush = CreateSolidBrush(RGB(0,255,0));
HBRUSH black_brush = CreateSolidBrush(RGB(0,0,0));

// starting position of ball
int ball_x = WINDOW_WIDTH/2;
int ball_y = WINDOW_HEIGHT/2;

// initial velocity of ball
int xv = -4+rand()%8;
int yv = -4+rand()%8;

// 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

    // ERASE the last position of the ball
   
    // first select the black pen and brush into context
    SelectObject(hdc, black_pen);
    SelectObject(hdc, black_brush);

    // draw the ball
    Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32);
   
    // MOVE the ball
    ball_x+=xv;
    ball_y+=yv;

    // test for collisions, first x-axis
    if (ball_x < 0 || ball_x > WINDOW_WIDTH - 32)
       {
       // invert x-velocity of ball
       xv=-xv;

       // push ball back
       ball_x+=xv;

       } // end if
    else
    // test for y-axis collisions
    if (ball_y < 0 || ball_y > WINDOW_HEIGHT - 32)
       {
       // invert y-velocity of ball
       yv=-yv;

       // push ball back
       ball_y+=yv;

       } // end if

    // now select the green and white colors for brush and pen
    SelectObject(hdc, white_pen);
    SelectObject(hdc, green_brush);

    // DRAW the ball
    Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32);

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

    // slow system down a little
    Sleep(10);
      
 } // end while

// delete all the objects
DeleteObject(white_pen);
DeleteObject(black_pen);
DeleteObject(green_brush);
DeleteObject(black_brush);

// release the device context
ReleaseDC(hwnd,hdc);

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

} // end WinMain

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

2.绘制多边形
绘制多边形的程序是Polygon()
原型:BOOL Polygon(HDC hdc,
                  CONST POINT *lpPoints,
                  int nCount);
只要向Polygon()传递一个POINT的列表及其数量，就可以使用当前的画笔和画刷绘制一个闭合的多边形