윈도우 자석효과 (GetSystemMetrics)

#include <windows.h>

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

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=0;
    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);

    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)
{
    HDC hdc;
    PAINTSTRUCT ps;
    static int sx,sy;
    int t;
    char str[]="화면 가장자리에 밀착합니다.";
    switch(iMessage) {
    case WM_CREATE:
        sx=GetSystemMetrics(SM_CXSCREEN);        // 자석 효과
        sy=GetSystemMetrics(SM_CYSCREEN);
        return 0;
    case WM_WINDOWPOSCHANGING:                    // 윈도우 이동시
        t=((LPWINDOWPOS)lParam)->x;
        if (t < 30) t=0;
        if (t+((LPWINDOWPOS)lParam)->cx > sx-30)    // 하위 4비트를 무조건 0으로 만들기
            t=sx-((LPWINDOWPOS)lParam)->cx;
        ((LPWINDOWPOS)lParam)->x=t;

        t=((LPWINDOWPOS)lParam)->y;
        if (t < 30) t=0;
        if (t+((LPWINDOWPOS)lParam)->cy > sy-30)
            t=sy-((LPWINDOWPOS)lParam)->cy;
        ((LPWINDOWPOS)lParam)->y=t;
        return 0;
    case WM_PAINT:
        hdc=BeginPaint(hWnd, &ps);
        TextOut(hdc,100,100,str,strlen(str));
        EndPaint(hWnd, &ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}
//*/

/*
LRESULT CALLBACK WndProc(HWND hWnd,UINT iMessage,WPARAM wParam,LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    char str[]="16픽셀 단위로만 움직입니다.";
    switch(iMessage) {
    case WM_WINDOWPOSCHANGING:
        ((LPWINDOWPOS)lParam)->x &= 0xfff0;
        ((LPWINDOWPOS)lParam)->y &= 0xfff0;
        ((LPWINDOWPOS)lParam)->cx &= 0xfff0;
        ((LPWINDOWPOS)lParam)->cy &= 0xfff0;
        return 0;
    case WM_PAINT:
        hdc=BeginPaint(hWnd, &ps);
        TextOut(hdc,100,100,str,strlen(str));
        EndPaint(hWnd, &ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}
//*/