차일드 윈도우3 (child)

#include <windows.h>

LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
LRESULT CALLBACK ChildProc(HWND,UINT,WPARAM,LPARAM);
HINSTANCE g_hInst;
LPSTR lpszClass="ChildWnd2";

int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance
         ,LPSTR lpszCmdParam,int nCmdShow)
{
    HWND hWnd;
    MSG Message;
    WNDCLASS WndClass;
    g_hInst=hInstance;
    
    WndClass.cbClsExtra=0;
    WndClass.cbWndExtra=4;        // 윈도우에 4byte의 추가 메모리를 할당한다.
    WndClass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
    WndClass.hCursor=LoadCursor(NULL,IDC_ARROW);
    WndClass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
    WndClass.hInstance=hInstance;
    WndClass.lpfnWndProc=(WNDPROC)WndProc;
    WndClass.lpszClassName=lpszClass;
    WndClass.lpszMenuName=NULL;
    WndClass.style=CS_HREDRAW | CS_VREDRAW;
    RegisterClass(&WndClass);

    WndClass.hCursor=LoadCursor(NULL,IDC_CROSS);
    WndClass.lpfnWndProc=(WNDPROC)ChildProc;
    WndClass.lpszClassName="ChildCls";
    WndClass.hbrBackground=(HBRUSH)GetStockObject(LTGRAY_BRUSH);
    RegisterClass(&WndClass);

    hWnd=CreateWindow(lpszClass,lpszClass,WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,
        NULL,(HMENU)NULL,hInstance,NULL);
    ShowWindow(hWnd,nCmdShow);
    
    while(GetMessage(&Message,0,0,0)) {
        TranslateMessage(&Message);
        DispatchMessage(&Message);
    }
    return Message.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd,UINT iMessage,WPARAM wParam,LPARAM lParam)
{
    int x,y;
    switch(iMessage) {
    case WM_CREATE:
        for (x=0;x<300;x+=100)
            for (y=0;y<300;y+=100) {
                CreateWindow("ChildCls",NULL,WS_CHILD | WS_VISIBLE,
                x,y,100,100,hWnd,(HMENU)NULL,g_hInst,NULL);
            }
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}

LRESULT CALLBACK ChildProc(HWND hWnd,UINT iMessage,WPARAM wParam,LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    switch(iMessage) {
    case WM_CREATE:
        SetWindowLong(hWnd, 0, 0);        // 윈도우클래스나 윈도우에 여분으로 할당된 메모리를 읽고 쓰기
        // 기존으로 0값을 넣었는데
        return 0;
    case WM_LBUTTONDOWN:
        // 해당 핸들 hWnd 의 메모리를 not 시켜서 set을 하므로 1을 넣게 되고
        // InvalidateRect를 실행 WM_PAINT를 실행시킨다.
        SetWindowLong(hWnd,0,!GetWindowLong(hWnd,0));        
        InvalidateRect(hWnd,NULL,TRUE);
        return 0;
    case WM_PAINT:
        hdc=BeginPaint(hWnd, &ps);
        if (GetWindowLong(hWnd,0))
            Ellipse(hdc,0,0,100,100);
        else
            Rectangle(hdc,0,0,100,100);
        EndPaint(hWnd, &ps);
        return 0;
    }
    return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}