《Windows程序设计》第七章BlockOut2的问题
/*---------------------------------------------------
BLOKOUT2.C -- Mouse Button & Capture Demo Program
(c) Charles Petzold, 1998
---------------------------------------------------*/

#include <windows.h>

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT ("BlokOut2") ;
HWND hwnd ;
MSG msg ;
WNDCLASS wndclass ;

wndclass.style = CS_HREDRAW | CS_VREDRAW ;
wndclass.lpfnWndProc = WndProc ;
wndclass.cbClsExtra = 0 ;
wndclass.cbWndExtra = 0 ;
wndclass.hInstance = hInstance ;
wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ;
wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;
wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
wndclass.lpszMenuName = NULL ;
wndclass.lpszClassName = szAppName ;

if (!RegisterClass (&wndclass))
{
MessageBox (NULL, TEXT ("Program requires Windows NT!"),
szAppName, MB_ICONERROR) ;
return 0 ;
}

hwnd = CreateWindow (szAppName, TEXT ("Mouse Button & Capture Demo"),
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT,
NULL, NULL, hInstance, NULL) ;

ShowWindow (hwnd, iCmdShow) ;
UpdateWindow (hwnd) ;

while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg) ;
DispatchMessage (&msg) ;
}
return msg.wParam ;
}

void DrawBoxOutline (HWND hwnd, POINT ptBeg, POINT ptEnd)
{
HDC hdc ;

hdc = GetDC (hwnd) ;

SetROP2 (hdc, R2_NOT) ;
SelectObject (hdc, GetStockObject (NULL_BRUSH)) ;
Rectangle (hdc, ptBeg.x, ptBeg.y, ptEnd.x, ptEnd.y) ;

ReleaseDC (hwnd, hdc) ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
static BOOL fBlocking, fValidBox ;
static POINT ptBeg, ptEnd, ptBoxBeg, ptBoxEnd ;
HDC hdc ;
PAINTSTRUCT ps ;

switch (message)
{
case WM_LBUTTONDOWN :
ptBeg.x = ptEnd.x = LOWORD (lParam) ;
ptBeg.y = ptEnd.y = HIWORD (lParam) ;

DrawBoxOutline (hwnd, ptBeg, ptEnd) ;

SetCapture (hwnd) ;
SetCursor (LoadCursor (NULL, IDC_CROSS)) ;

fBlocking = TRUE ;
return 0 ;

case WM_MOUSEMOVE :
if (fBlocking)
{
SetCursor (LoadCursor (NULL, IDC_CROSS)) ;

DrawBoxOutline (hwnd, ptBeg, ptEnd) ;

ptEnd.x = LOWORD (lParam) ;
ptEnd.y = HIWORD (lParam) ;

DrawBoxOutline (hwnd, ptBeg, ptEnd) ;

}
return 0 ;

case WM_LBUTTONUP :
if (fBlocking)
{
DrawBoxOutline (hwnd, ptBeg, ptEnd) ;

ptBoxBeg = ptBeg ;
ptBoxEnd.x = LOWORD (lParam) ;
ptBoxEnd.y = HIWORD (lParam) ;

ReleaseCapture () ;
SetCursor (LoadCursor (NULL, IDC_ARROW)) ;

fBlocking = FALSE ;
fValidBox = TRUE ;

InvalidateRect (hwnd, NULL, TRUE) ;
}
return 0 ;

case WM_CHAR :
if (fBlocking & (wParam == '\x1B')) // i.e., Escape
{
DrawBoxOutline (hwnd, ptBeg, ptEnd) ;

ReleaseCapture () ;
SetCursor (LoadCursor (NULL, IDC_ARROW)) ;

fBlocking = FALSE ;
}
return 0 ;

case WM_PAINT :
hdc = BeginPaint (hwnd, &ps) ;

if (fValidBox)
{
SelectObject (hdc, GetStockObject (BLACK_BRUSH)) ;
Rectangle (hdc, ptBoxBeg.x, ptBoxBeg.y,
ptBoxEnd.x, ptBoxEnd.y) ;
}

if (fBlocking)
{
SetROP2 (hdc, R2_NOT) ;
SelectObject (hdc, GetStockObject (NULL_BRUSH)) ;
Rectangle (hdc, ptBeg.x, ptBeg.y, ptEnd.x, ptEnd.y) ;
}

EndPaint (hwnd, &ps) ;
return 0 ;

case WM_DESTROY :
PostQuitMessage (0) ;
return 0 ;
}
return DefWindowProc (hwnd, message, wParam, lParam) ;
}

当把鼠标拖动到客户区左边或上边时，画出来的矩形不是想象的样子，不知道为什么会出现这个问题，或者怎么解决呢？希望朋友帮忙解释一下，谢谢。


[解决办法]
画出来的矩形大致什么样子的呢？
[解决办法]
判断一下鼠标边界好了简单改了一下，那个2000是我设的比屏幕分辨率要大的值。

C/C++ code

case WM_MOUSEMOVE :        if (fBlocking)        {            SetCursor (LoadCursor (NULL, IDC_CROSS)) ;                        DrawBoxOutline (hwnd, ptBeg, ptEnd) ;                        ptEnd.x = LOWORD (lParam) ;            ptEnd.y = HIWORD (lParam) ;            if(ptEnd.x>2000) ptEnd.x=0;///此二行判断            if(ptEnd.y>2000) ptEnd.y=0;///            DrawBoxOutline (hwnd, ptBeg, ptEnd) ;        }        return 0 ;            case WM_LBUTTONUP :        if (fBlocking)        {            DrawBoxOutline (hwnd, ptBeg, ptEnd) ;                        ptBoxBeg = ptBeg ;            ptBoxEnd.x = LOWORD (lParam) ;            ptBoxEnd.y = HIWORD (lParam) ;            if(ptBoxEnd.x>2000) ptBoxEnd.x=0;////同上            if(ptBoxEnd.y>2000) ptBoxEnd.y=0;////            ReleaseCapture () ;            SetCursor (LoadCursor (NULL, IDC_ARROW)) ;                        fBlocking = FALSE ;            fValidBox = TRUE ;                        InvalidateRect (hwnd, NULL, TRUE) ;        }        return 0 ;