Chương trình ObjectDrag V2

Chương trinh ban đầu vẽ một hình elip. Sau đó người sử dụng có thể di chuyển bằng cách kéo lê. Khác bài ObjectDrag trước, là có dùng R2_XORPEN và R2_NOTXORPEN để chống chớp chương trình.

/// ObjectDrag2.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "resource.h"

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;        // current instance
TCHAR szTitle[MAX_LOADSTRING];        // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];        // The title bar text

// Foward declarations of functions included in this code module:
ATOM    MyRegisterClass(HINSTANCE hInstance);
BOOL    InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
  // TODO: Place code here.
 MSG msg;
 HACCEL hAccelTable;

 // Initialize global strings
 LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
 LoadString(hInstance, IDC_OBJECTDRAG2, szWindowClass, MAX_LOADSTRING);
 MyRegisterClass(hInstance);

 // Perform application initialization:
 if (!InitInstance (hInstance, nCmdShow)) 
 {
  return FALSE;
 }

 hAccelTable = LoadAccelerators(hInstance, (LPCTSTR)IDC_OBJECTDRAG2);

 // Main message loop:
 while (GetMessage(&msg, NULL, 0, 0)) 
 {
  if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) 
  {
   TranslateMessage(&msg);
   DispatchMessage(&msg);
  }
 }

 return msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
//  COMMENTS:
//
//    This function and its usage is only necessary if you want this code
//    to be compatible with Win32 systems prior to the 'RegisterClassEx'
//    function that was added to Windows 95. It is important to call this function
//    so that the application will get 'well formed' small icons associated
//    with it.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
 WNDCLASSEX wcex;

 wcex.cbSize = sizeof(WNDCLASSEX); 

 wcex.style   = CS_HREDRAW | CS_VREDRAW;
 wcex.lpfnWndProc = (WNDPROC)WndProc;
 wcex.cbClsExtra  = 0;
 wcex.cbWndExtra  = 0;
 wcex.hInstance  = hInstance;
 wcex.hIcon   = LoadIcon(hInstance, (LPCTSTR)IDI_OBJECTDRAG2);
 wcex.hCursor  = LoadCursor(NULL, IDC_ARROW);
 wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
 wcex.lpszMenuName = (LPCSTR)IDC_OBJECTDRAG2;
 wcex.lpszClassName = szWindowClass;
 wcex.hIconSm  = LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL);

 return RegisterClassEx(&wcex);
}

//
//   FUNCTION: InitInstance(HANDLE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   HWND hWnd;

   hInst = hInstance; // Store instance handle in our global variable

   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, unsigned, WORD, LONG)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_COMMAND - process the application menu
//  WM_PAINT - Paint the main window
//  WM_DESTROY - post a quit message and return
//
//

// <==
bool IsInsideEllipse(int x1, int y1, int x2, int y2, int x, int y) 
{ 
 double a = (double(x2)-x1)/2, b = (double(y2)-y1)/2; 
 if (!a || !b) return false; 
 double xx = x - (double(x1)+x2)/2, yy = y - (double(y1)+y2)/2; 
 double xr = xx/a, yr = yy/b; 
 return xr*xr+yr*yr <= 1; 
} 
// ==>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
 int wmId, wmEvent;
 PAINTSTRUCT ps;
 HDC hdc;
 TCHAR szHello[MAX_LOADSTRING];
 LoadString(hInst, IDS_HELLO, szHello, MAX_LOADSTRING);

 // 

 switch (message) 
 {
  
  // <==
  case WM_CREATE: 
   GetClientRect(hWnd, &rt); 
   x1 = rt.right/4; x2 = 3*rt.right/4; 
   y1 = rt.bottom/4; y2 = 3*rt.bottom/4; 
   hbr = CreateHatchBrush(HS_DIAGCROSS, RGB(255,0,0)); 
   hCursorMove = LoadCursor(NULL, IDC_SIZEALL); 
   hPenDot = CreatePen(PS_DOT, 1, RGB(0,0,255)); 
   break; 
  // ==>

  case WM_COMMAND:
   wmId    = LOWORD(wParam); 
   wmEvent = HIWORD(wParam); 
   // Parse the menu selections:
   switch (wmId)
   {
    case IDM_ABOUT:
       DialogBox(hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, (DLGPROC)About);
       break;
    case IDM_EXIT:
       DestroyWindow(hWnd);
       break;
    default:
       return DefWindowProc(hWnd, message, wParam, lParam);
   }
   break;

  // <==
  case WM_LBUTTONDOWN: 
   xc = LOWORD(lParam); yc = HIWORD(lParam); 
   if (IsInsideEllipse(x1,y1,x2,y2,xc,yc)) 
   { 
    hdc = GetDC(hWnd); 
    SelectObject(hdc,hPenDot); 
    SetROP2(hdc, R2_NOTXORPEN); 
    Ellipse(hdc,x1,y1,x2,y2); 
    SetCursor(hCursorMove); 
    SetCapture(hWnd); 
   } 
   break; 

  case WM_MOUSEMOVE: 
   if (GetCapture() == hWnd) 
   { 
    hdc = GetDC(hWnd); 
    SelectObject(hdc,hPenDot); 
    SetROP2(hdc, R2_NOTXORPEN); 
    Ellipse(hdc,x1,y1,x2,y2); 
 
    px = xc; py = yc; 
    xc = LOWORD(lParam); yc = HIWORD(lParam); 
    dx = xc-px, dy = yc - py; 
    x1 += dx, x2 += dx, 
    y1 += dy, y2 += dy; 
    Ellipse(hdc,x1,y1,x2,y2); 
   } 
   break; 

  case WM_LBUTTONUP: 
   if (GetCapture() == hWnd) 
   { 
    ReleaseCapture(); 
    InvalidateRect(hWnd, NULL, TRUE); 
   } 
   break; 
  // ==>

  case WM_PAINT:
   hdc = BeginPaint(hWnd, &ps);
   // TODO: Add any drawing code here...
   RECT rt;
   GetClientRect(hWnd, &rt);
   DrawText(hdc, szHello, strlen(szHello), &rt, DT_CENTER);

   // <==
   SelectObject(hdc,hbr); 
   Ellipse(hdc,x1,y1,x2,y2);
   // ==>

   EndPaint(hWnd, &ps);
   break;
  case WM_DESTROY:
   PostQuitMessage(0);
   break;
  default:
   return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}

// Mesage handler for about box.
LRESULT CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
 switch (message)
 {
  case WM_INITDIALOG:
    return TRUE;

  case WM_COMMAND:
   if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL) 
   {
    EndDialog(hDlg, LOWORD(wParam));
    return TRUE;
   }
   break;
 }
    return FALSE;
}