sdk问题

[World7th]

/*----------------------------------------------------------------------------
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) ;
}


在WM_MOUSEMOVE消息中，为什么必须出现两个DrawBoxOutline函数？为什么不能只含有第二个DrawBoxOutline函数。比如：

case WM_MOUSEMOVE :

if (fBlocking)
{
SetCursor (LoadCursor (NULL, IDC_CROSS)) ;

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

DrawBoxOutline (hwnd, ptBeg, ptEnd) ;
}

return 0 ;
大家把这段程序调试一下，解决我的问题，可以么？谢谢了

[菜牛]

两次调用坐标不同了呀。

[World7th]

楼上的，能不能说清楚一点，我刚学sdk，不怎么懂。你能不能帮我试试看，如果去掉第一个DrawBoxOutline函数，执行效果会变的很奇妙，不知道什么原因，可以说说里面的实质么？建议大家调试一下。

[horisly]

这里主要是用到了 SetROP2 函数的原因。

SetROP2
The SetROP2 function sets the current foreground mix mode. GDI uses the foreground mix mode to combine pens and interiors of filled objects with the colors already on the screen. The foreground mix mode defines how colors from the brush or pen and the colors in the existing image are to be combined.


＝＝＝＝＝＝＝＝＝＝＝＝

WM_MOUSEMOVE消息中，为什么必须出现两个DrawBoxOutline函数？

＝＝》》前一个DrawBoxOutline是用来把之前画的block覆盖了，使其恢复背景的颜色，
然后第二个DrawBoxOutline才是在新的位置画矩形的