在MFC SDI程序中使用SDL

SDL的设计并没有考虑到要和MFC相结合，但是既然它要在windows的系统上运行，必然需要使用Windows提供的API。为了在MFC SDI中使用SDL，首先想到的就是替换SDL创建的窗口，改为使用MFC提供的窗口。

想想在Windows下要创建窗口需要使用的API必然是CreateWindow，在SDL代码中搜，很容易发现了这样一段代码：

int DIB_CreateWindow(_THIS)
{
char *windowid = SDL_getenv("SDL_WINDOWID");

SDL_RegisterApp(NULL, 0, 0);

SDL_windowid = (windowid != NULL);
if ( SDL_windowid ) {
#if defined(_WIN32_WCE) && (_WIN32_WCE < 300)
/* wince 2.1 does not have strtol */
wchar_t *windowid_t = SDL_malloc((SDL_strlen(windowid) + 1) * sizeof(wchar_t));
MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, windowid, -1, windowid_t, SDL_strlen(windowid) + 1);
SDL_Window = (HWND)wcstol(windowid_t, NULL, 0);
SDL_free(windowid_t);
#else
SDL_Window = (HWND)SDL_strtoull(windowid, NULL, 0);
#endif
if ( SDL_Window == NULL ) {
SDL_SetError("Couldn't get user specified window");
return(-1);
}

/* DJM: we want all event's for the user specified
window to be handled by SDL.
*/
userWindowProc = (WNDPROCTYPE)GetWindowLongPtr(SDL_Window, GWLP_WNDPROC);
SetWindowLongPtr(SDL_Window, GWLP_WNDPROC, (LONG_PTR)WinMessage);
} else {
SDL_Window = CreateWindow(SDL_Appname, SDL_Appname,
(WS_OVERLAPPED|WS_CAPTION|WS_SYSMENU|WS_MINIMIZEBOX),
CW_USEDEFAULT, CW_USEDEFAULT, 0, 0, NULL, NULL, SDL_Instance, NULL);
if ( SDL_Window == NULL ) {
SDL_SetError("Couldn't create window");
return(-1);
}
ShowWindow(SDL_Window, SW_HIDE);
}

/* JC 14 Mar 2006
Flush the message loop or this can cause big problems later
Especially if the user decides to use dialog boxes or assert()!
*/
WIN_FlushMessageQueue();

return(0);
}
注意到前面的if条件判断使用了SDL_windowid，如果这个变量不为0，那么SDL是不会创建新窗口的！而这个值直接来自于SDL_WINDOWID这个环境变量！以此推断，只要在调用SDL_Init之前设置好SDL_WINDOWID这个环境变量，那么SDL将可以使用我们提供的窗口。

下面修改SDL提供的testwin示例，使之在MFC SDI环境下运行。

1.1 工程创建

直接使用VS2008的向导生成一个叫sdi_sdl的MFC工程，选择SDI类型。

1.2 抛弃SDLmain.lib

在SDL提供的测试用例中，都要使用SDLmain.lib，这个lib文件实现了Winmain和main这两个入口函数，在这两个函数中进行了一些SDL的初始化工作。而在MFC下，我们不需要自己写WinMain，因此直接抛弃SDLmain.lib，将相关的代码转移到Csdi_sdlView的OnCreate函数中。之所以选择Csdi_sdlView::OnCreate是因为此时窗口已经创建，可以取到这个窗口的Handle，从而可以在SDL初始化之前设置好Window id。

int Csdi_sdlView::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
if (CView::OnCreate(lpCreateStruct) == -1)
return -1;

char variable[256];
sprintf(variable, "SDL_WINDOWID=0x%lx",
this->GetSafeHwnd());
SDL_putenv(variable);
SDL_WinMain(AfxGetApp()->m_hInstance, NULL, AfxGetApp()->m_lpCmdLine, SW_MAXIMIZE);
return 0;
}

1.3 SDL_WinMain

这个函数来源于SDLmain中的WinMain函数，只是删除了一些不必要的代码：

/* This is where execution begins [windowed apps] */
int Csdi_sdlView::SDL_WinMain(HINSTANCE hInst, HINSTANCE hPrev, LPSTR szCmdLine,
int sw)
{
HINSTANCE handle;
char **argv;
int argc;
char *cmdline;
char *bufp;
size_t nLen;

/* Start up DDHELP.EXE before opening any files, so DDHELP doesn't
keep them open. This is a hack.. hopefully it will be fixed

someday. DDHELP.EXE starts up the first time DDRAW.DLL is loaded.
*/
handle = LoadLibrary(TEXT("DDRAW.DLL"));
if ( handle != NULL ) {
FreeLibrary(handle);
}

/* Grab the command line */
bufp = GetCommandLine();
nLen = SDL_strlen(bufp)+1;
cmdline = SDL_stack_alloc(char, nLen);
SDL_strlcpy(cmdline, bufp, nLen);

/* Parse it into argv and argc */
argc = ParseCommandLine(cmdline, NULL);
argv = SDL_stack_alloc(char*, argc+1);
ParseCommandLine(cmdline, argv);

/* Run the main program (after a little SDL initialization) */
SDL_PreMain(argc, argv);

/* Hush little compiler, don't you cry... */
return 0;
}

1.4 SDL_PreMain

这个函数来源于sdlmain.lib中的main函数：

/* This is where execution begins [console apps] */
int Csdi_sdlView::SDL_PreMain(int argc,
char *argv[])
{
size_t n;
char *bufp, *appname;
int status;

/* Get the class name from argv[0] */
appname = argv[0];
if ( (bufp=SDL_strrchr(argv[0],
'//')) != NULL ) {
appname = bufp+1;
} else
if ( (bufp=SDL_strrchr(argv[0],
'/')) != NULL ) {
appname = bufp+1;
}

if ( (bufp=SDL_strrchr(appname,
'.')) == NULL )
n = SDL_strlen(appname);
else
n = (bufp-appname);

bufp = SDL_stack_alloc(char, n+1);
SDL_strlcpy(bufp, appname, n+1);
appname = bufp;

///* Load SDL dynamic link library */
//if ( SDL_Init(SDL_INIT_NOPARACHUTE) < 0 ) {
// ShowError("WinMain() error", SDL_GetError());
// return(FALSE);
//}

/* Sam:
We still need to pass in the application handle so that
DirectInput will initialize properly when SDL_RegisterApp()
is called later in the video initialization.
*/
SDL_SetModuleHandle(GetModuleHandle(NULL));

/* Run the application main() code */
status = SDL_main(argc, argv);

/* Hush little compiler, don't you cry... */
return 0;
}

1.5 SDL_main

这个函数来自于testwin示例中的main函数，只是在末尾删除了SDL_Quit这样的退出语句。

int Csdi_sdlView::SDL_main(int argc,
char *argv[])
{
SDL_Surface *screen;

/* Options */
int speedy, flip, nofade;
int delay;
int w, h;
int desired_bpp;
Uint32 video_flags;

/* Set default options and check command-line */
speedy = 0;
flip = 0;
nofade = 0;
delay = 1;

RECT rc;
this->GetWindowRect(&rc);
w = rc.right;
h = rc.bottom;
desired_bpp = 0;
video_flags = 0;
if ( SDL_Init(SDL_INIT_VIDEO | SDL_INIT_NOPARACHUTE) < 0 ) {
ShowError("Couldn't initialize SDL", SDL_GetError());
return(1);
}

/* Initialize the display */
screen = SDL_SetVideoMode(w, h, desired_bpp, video_flags);
if ( screen == NULL ) {
ShowError("Couldn't set %dx%dx%d video mode: %s/n",
"");
return (1);
}

DrawPict(screen, argv[1], speedy, flip, nofade);
// SDL_Delay(delay*1000);
// SDL_Quit();
return(0);
}
至此，这个程序就可以正常运行了，但是它的大小还不能随主窗口的变化而变化。为此还需要响应WM_SIZE：

void Csdi_sdlView::OnSize(UINT nType,
int cx, int cy)
{
SDL_Surface *screen;
screen = SDL_SetVideoMode(cx, cy, 0, 0);
DrawPict(screen, NULL, 0, 0, 0);
}

1.6 SDL_Quit

在程序退出的时候，需要调用SDL_Quit进行一些清理的工作，原来想将这个工作放在Cview::OnDestroy中完成，但是发现这样有很多的内存泄漏。最后将其放在Csdi_sdlApp:ExitInstance中完成：

BOOL Csdi_sdlApp::ExitInstance()
{
SDL_Quit();
return TRUE;
}
即便是这样，仍然有一处内存泄漏，原因不明：

Detected memory leaks!
Dumping objects ->
{98} normal block at 0x003D37C0, 21 bytes long.
Data: <0x40784 OWID 0x4> 30 78 34 30 37 38 34 00 4F 57 49 44 00 30 78 34

Object dump complete.



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