Программирование графики

#include <iostream>
#include <windows.h>
#include "resource.h"
using namespace std;
 
int x1, y1, x2, y2;
 
int WINAPI DlgProc( HWND hDlg, WORD wMsg, WORD wParam, DWORD )
{
    PAINTSTRUCT ps;
 
    if( wMsg == WM_CLOSE || wMsg == WM_COMMAND && wParam == IDOK ) {
        EndDialog(hDlg,0);
    } else
    if( wMsg == WM_INITDIALOG ) {
        RECT rc;
        GetClientRect(hDlg,&rc);
        int dx = rc.right - rc.left;
        int dy = rc.bottom- rc.top;
    } else
    if( wMsg == WM_PAINT ) {
        BeginPaint(hDlg,&ps);
        HPEN hPen = (HPEN)CreatePen(PS_SOLID,1,RGB(0,0,255));
        HPEN hOldPen = (HPEN)SelectObject(ps.hdc,hPen);
 
        POINT ptOld;
        MoveToEx(ps.hdc,x1,y1,&ptOld);
        LineTo(ps.hdc,x2,y2);
 
        SelectObject(ps.hdc,hOldPen);
        DeleteObject(hPen);
        EndPaint(hDlg,&ps);
    }
    return 0;
}
 
void main()
{
 
    cout << "Please, enter 4 coords:\n" << flush;
 
    cin >> x1 >> y1 >> x2 >> y2;
    cout << "x1 = " << x1 << "\ny1 = " << y1 
         << "\nx2 = " << x2 << "\ny2 = " << y2 << "\n" << flush;
 
  
    DialogBox(NULL,MAKEINTRESOURCE(IDD_DIALOG1),NULL,(DLGPROC)DlgProc);
}