드래그 (drag, ImageList_BeginDrag, ClientToScreen, ImageList_DragEnter, ImageList_DragMove, ImageList_DragLeave, ImageList_EndDrag)

#include <windows.h>

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

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);
    hWndMain=hWnd;
    
    while(GetMessage(&Message,0,0,0)) {
        TranslateMessage(&Message);
        DispatchMessage(&Message);
    }
    return Message.wParam;
}

#include <commctrl.h>
#include "resource.h"
HIMAGELIST IL;
BOOL bDrag;                // TRUE=현재 드래그 중
int x=100,y=100;        // 현재 위치
int hotx,hoty;            // 핫 스팟 좌표
LRESULT CALLBACK WndProc(HWND hWnd,UINT iMessage,WPARAM wParam,LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    HBRUSH hBrush;
    RECT rt;
    POINT pt;

    switch(iMessage) {
    case WM_CREATE:
        bDrag=FALSE;
        InitCommonControls();
        IL=ImageList_LoadBitmap(g_hInst, MAKEINTRESOURCE(IDB_DRAGIMAGE),
            32, 1, RGB(255,255,255));
        return 0;
    case WM_LBUTTONDOWN:
        pt.x=LOWORD(lParam);
        pt.y=HIWORD(lParam);
        if (pt.x >= x && pt.x <=x+32 && pt.y >= y && pt.y <= y+32) {
            // 출력되어 있는 이미지를 먼저 지운다.
            hBrush=CreateSolidBrush(GetSysColor(COLOR_WINDOW));
            SetRect(&rt,x,y,x+32,y+32);
            hdc=GetDC(hWnd);
            FillRect(hdc,&rt,hBrush);
            ReleaseDC(hWnd,hdc);
            DeleteObject(hBrush);

            // 핫 스팟을 계산하고 드래그를 시작한다.
            hotx=pt.x-x;
            hoty=pt.y-y;
            ImageList_BeginDrag(IL,0,hotx,hoty);
            bDrag=TRUE;
            ClientToScreen(hWnd,&pt);
            ImageList_DragEnter(GetDesktopWindow(),pt.x,pt.y);
            SetCapture(hWnd);                            // 이미지가 밖으로 나가도 이상없게해주고
        }
        return 0;
    case WM_MOUSEMOVE:
        if (bDrag) {
            GetCursorPos(&pt);
            ImageList_DragMove(pt.x,pt.y);        // Image 가 drag되는 경로는 표현해야지..
        }
        return 0;
    case WM_LBUTTONUP:
        if (bDrag) {
            ImageList_DragLeave(GetDesktopWindow());    // 이미지를 떠나보내고
            ImageList_EndDrag();
            bDrag=FALSE;
            GetCursorPos(&pt);
            ScreenToClient(hWnd,&pt);
            x=pt.x-hotx;
            y=pt.y-hoty;
            if (x < 0) x=10;
            if (y < 0) y=10;
            InvalidateRect(hWnd,NULL,TRUE);
            ReleaseCapture();                            //
        }
    case WM_PAINT:
        hdc=BeginPaint(hWnd, &ps);
        ImageList_Draw(IL,0,hdc,x,y,ILD_NORMAL);        // Drag 시 이미즈를 반투명하니 보여주도록 한다.
        EndPaint(hWnd, &ps);
        return 0;
    case WM_DESTROY:
        ImageList_Destroy(IL);
        PostQuitMessage(0);
        return 0;
    }
    return(DefWindowProc(hWnd,iMessage,wParam,lParam));
}