SDL播放视频的代码流程如下所示。
初始化:
SDL_Init(): 初始化SDL。
SDL_CreateWindow(): 创建窗口（Window）。
SDL_CreateRenderer(): 基于窗口创建渲染器（Render）。
SDL_CreateTexture(): 创建纹理（Texture）。
循环渲染数据:
SDL_UpdateTexture(): 设置纹理的数据。
SDL_RenderCopy(): 纹理复制给渲染器。SDL_RenderPresent(): 显示。
上篇文章分析了该流程中的第一个函数SDL_Init()。本文继续分析该流程中的第二个函数SDL_CreateWindow()。
SDL_Window
SDL_Window结构体定义了一个SDL2中的窗口。如果直接使用SDL2编译好的SDK的话，是看不到它的内部结构的。有关它的定义在头文件中只有一行代码，但是这一行定义前面的注释非常之多，如下所示：
/** * \brief The type used to identify a window * * \sa SDL_CreateWindow() * \sa SDL_CreateWindowFrom() * \sa SDL_DestroyWindow() * \sa SDL_GetWindowData() * \sa SDL_GetWindowFlags() * \sa SDL_GetWindowGrab() * \sa SDL_GetWindowPosition() * \sa SDL_GetWindowSize() * \sa SDL_GetWindowTitle() * \sa SDL_HideWindow() * \sa SDL_MaximizeWindow() * \sa SDL_MinimizeWindow() * \sa SDL_RaiseWindow() * \sa SDL_RestoreWindow() * \sa SDL_SetWindowData() * \sa SDL_SetWindowFullscreen() * \sa SDL_SetWindowGrab() * \sa SDL_SetWindowIcon() * \sa SDL_SetWindowPosition() * \sa SDL_SetWindowSize() * \sa SDL_SetWindowBordered() * \sa SDL_SetWindowTitle() * \sa SDL_ShowWindow() */ typedef struct SDL_Window SDL_Window;
在源代码工程中可以看到它的定义，位于video\SDL_sysvideo.h文件中。它的定义如下。
/* Define the SDL window structure, corresponding to toplevel windows */
struct SDL_Window
{
const void *magic;
Uint32 id;
char *title;
SDL_Surface *icon;
int x, y;
int w, h;
int min_w, min_h;
int max_w, max_h;
Uint32 flags;
Uint32 last_fullscreen_flags;
/* Stored position and size for windowed mode */
SDL_Rect windowed;
SDL_DisplayMode fullscreen_mode;
float brightness;
Uint16 *gamma;
Uint16 *saved_gamma; /* (just offset into gamma) */
SDL_Surface *surface;
SDL_bool surface_valid;
SDL_bool is_destroying;
SDL_WindowShaper *shaper;
SDL_WindowUserData *data;
void *driverdata;
SDL_Window *prev;
SDL_Window *next;
};
可以看出其中包含了一个“窗口”应该包含的各种属性。这个结构体中的各个变量还没有深入研究，暂不详细分析。下面来看看如何创建这个SDL_Window。
SDL_CreateWindow()
函数简介
SDL_CreateWindow()用于创建一个视频播放的窗口。SDL_CreateWindow()的定义如下。
SDL_Window * SDLCALL SDL_CreateWindow(const char *title,
int x, int y, int w,
int h, Uint32 flags);
参数含义如下。
title ：窗口标题
x ：窗口位置x坐标。也可以设置为SDL_WINDOWPOS_CENTERED或SDL_WINDOWPOS_UNDEFINED。
y ：窗口位置y坐标。同上。
w ：窗口的宽
h ：窗口的高
flags ：支持下列标识。包括了窗口的是否最大化、最小化，能否调整边界等等属性。
::SDL_WINDOW_FULLSCREEN, ::SDL_WINDOW_OPENGL,
::SDL_WINDOW_HIDDEN, ::SDL_WINDOW_BORDERLESS,
::SDL_WINDOW_RESIZABLE, ::SDL_WINDOW_MAXIMIZED,
::SDL_WINDOW_MINIMIZED, ::SDL_WINDOW_INPUT_GRABBED,
::SDL_WINDOW_ALLOW_HIGHDPI.
返回创建完成的窗口的ID。如果创建失败则返回0。
源代码分析
SDL_CreateWindow()的源代码位于video\SDL_video.c中，如下所示。
SDL_Window * SDL_CreateWindow(const char *title, int x, int y, int w, int h, Uint32 flags)
{
SDL_Window *window;
const char *hint;
if (!_this) {
/* Initialize the video system if needed */
if (SDL_VideoInit(NULL) < 0) {
return NULL;
}
}
/* Some platforms can‘t create zero-sized windows */
if (w < 1) {
w = 1;
}
if (h < 1) {
h = 1;
}
/* Some platforms have OpenGL enabled by default */
#if (SDL_VIDEO_OPENGL && __MACOSX__) || __IPHONEOS__ || __ANDROID__
flags |= SDL_WINDOW_OPENGL;
#endif
if (flags & SDL_WINDOW_OPENGL) {
if (!_this->GL_CreateContext) {
SDL_SetError("No OpenGL support in video driver");
return NULL;
}
if (SDL_GL_LoadLibrary(NULL) < 0) {
return NULL;
}
}
/* Unless the user has specified the high-DPI disabling hint, respect the
* SDL_WINDOW_ALLOW_HIGHDPI flag.
*/
if (flags & SDL_WINDOW_ALLOW_HIGHDPI) {
hint = SDL_GetHint(SDL_HINT_VIDEO_HIGHDPI_DISABLED);
if (hint && SDL_atoi(hint) > 0) {
flags &= ~SDL_WINDOW_ALLOW_HIGHDPI;
}
}
window = (SDL_Window *)SDL_calloc(1, sizeof(*window));
if (!window) {
SDL_OutOfMemory();
return NULL;
}
window->magic = &_this->window_magic;
window->id = _this->next_object_id++;
window->x = x;
window->y = y;
window->w = w;
window->h = h;
if (SDL_WINDOWPOS_ISUNDEFINED(x) || SDL_WINDOWPOS_ISUNDEFINED(y) ||
SDL_WINDOWPOS_ISCENTERED(x) || SDL_WINDOWPOS_ISCENTERED(y)) {
SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
int displayIndex;
SDL_Rect bounds;
displayIndex = SDL_GetIndexOfDisplay(display);
SDL_GetDisplayBounds(displayIndex, &bounds);
if (SDL_WINDOWPOS_ISUNDEFINED(x) || SDL_WINDOWPOS_ISCENTERED(x)) {
window->x = bounds.x + (bounds.w - w) / 2;
}
if (SDL_WINDOWPOS_ISUNDEFINED(y) || SDL_WINDOWPOS_ISCENTERED(y)) {
window->y = bounds.y + (bounds.h - h) / 2;
}
}
window->flags = ((flags & CREATE_FLAGS) | SDL_WINDOW_HIDDEN);
window->last_fullscreen_flags = window->flags;
window->brightness = 1.0f;
window->next = _this->windows;
window->is_destroying = SDL_FALSE;
if (_this->windows) {
_this->windows->prev = window;
}
_this->windows = window;
if (_this->CreateWindow && _this->CreateWindow(_this, window) < 0) {
SDL_DestroyWindow(window);
return NULL;
}
if (title) {
SDL_SetWindowTitle(window, title);
}
SDL_FinishWindowCreation(window, flags);
/* If the window was created fullscreen, make sure the mode code matches */
SDL_UpdateFullscreenMode(window, FULLSCREEN_VISIBLE(window));
return window;
}
下面总结一下SDL_CreateWindow()的大致流程。
1. 一些为了保证各个平台的兼容性的初始化工作。各个平台创建窗口的条件不同。例如，某些平台不支持创建大小为0的窗口。再例如，某些平台默认开启OpenGL。
2. 调用SDL_calloc()为SDL_Window结构体分配一块内存。同时设置一些基本属性，例如窗口的宽高，位置等等。
PS：上篇文章中已经提过，在这里重复一下SDL中内存分配函数的知识。在SDL中分配内存使用SDL_malloc()，SDL_calloc()，这些函数实际上就是malloc()，calloc()。它们的定义位于stdlib\SDL_malloc.c文件中。如下所示：
#define memset SDL_memset #define memcpy SDL_memcpy #define malloc SDL_malloc #define calloc SDL_calloc #define realloc SDL_realloc #define free SDL_free
3. 调用VideoDevice的CreateWindow()方法创建窗口。这是创建窗口这个函数中最关键的一环。在这里有一点需要注意，SDL中有一个SDL_VideoDevice类型的静态全局变量_this。SDL调用视频驱动的功能都是通过调用该指针完成的。定义如下。
static SDL_VideoDevice *_this = NULL;
该_this变量代表了当前视频驱动设备。该变量在SDL_Init()中被赋值。如果是Windows下使用，则会被赋值为“Windows视频驱动”；Android下使用，则会被赋值为“Android视频驱动”。这是上篇文章中的内容，不再重复记录。
下面我们以“Windows视频驱动”为例，看看CreateWindow()都会执行哪些函数。
首先回顾一下上篇文章中的一个知识。从上一篇文章的SDL_Init()函数的分析中我们可以得知，Windows视频驱动初始化的时候会给SDL_VideoDevice一系列的函数指针赋值，如下所示。
static SDL_VideoDevice *WIN_CreateDevice(int devindex)
{
SDL_VideoDevice *device;
SDL_VideoData *data;
SDL_RegisterApp(NULL, 0, NULL);
/* Initialize all variables that we clean on shutdown */
device = (SDL_VideoDevice *) SDL_calloc(1, sizeof(SDL_VideoDevice));
if (device) {
data = (struct SDL_VideoData *) SDL_calloc(1, sizeof(SDL_VideoData));
} else {
data = NULL;
}
if (!data) {
SDL_free(device);
SDL_OutOfMemory();
return NULL;
}
device->driverdata = data;
data->userDLL = SDL_LoadObject("USER32.DLL");
if (data->userDLL) {
data->CloseTouchInputHandle = (BOOL (WINAPI *)( HTOUCHINPUT )) SDL_LoadFunction(data->userDLL, "CloseTouchInputHandle");
data->GetTouchInputInfo = (BOOL (WINAPI *)( HTOUCHINPUT, UINT, PTOUCHINPUT, int )) SDL_LoadFunction(data->userDLL, "GetTouchInputInfo");
data->RegisterTouchWindow = (BOOL (WINAPI *)( HWND, ULONG )) SDL_LoadFunction(data->userDLL, "RegisterTouchWindow");
}
/* Set the function pointers */
device->VideoInit = WIN_VideoInit;
device->VideoQuit = WIN_VideoQuit;
device->GetDisplayBounds = WIN_GetDisplayBounds;
device->GetDisplayModes = WIN_GetDisplayModes;
device->SetDisplayMode = WIN_SetDisplayMode;
device->PumpEvents = WIN_PumpEvents;
#undef CreateWindow
device->CreateWindow = WIN_CreateWindow;
device->CreateWindowFrom = WIN_CreateWindowFrom;
device->SetWindowTitle = WIN_SetWindowTitle;
device->SetWindowIcon = WIN_SetWindowIcon;
device->SetWindowPosition = WIN_SetWindowPosition;
device->SetWindowSize = WIN_SetWindowSize;
device->ShowWindow = WIN_ShowWindow;
device->HideWindow = WIN_HideWindow;
device->RaiseWindow = WIN_RaiseWindow;
device->MaximizeWindow = WIN_MaximizeWindow;
device->MinimizeWindow = WIN_MinimizeWindow;
device->RestoreWindow = WIN_RestoreWindow;
device->SetWindowBordered = WIN_SetWindowBordered;
device->SetWindowFullscreen = WIN_SetWindowFullscreen;
device->SetWindowGammaRamp = WIN_SetWindowGammaRamp;
device->GetWindowGammaRamp = WIN_GetWindowGammaRamp;
device->SetWindowGrab = WIN_SetWindowGrab;
device->DestroyWindow = WIN_DestroyWindow;
device->GetWindowWMInfo = WIN_GetWindowWMInfo;
device->CreateWindowFramebuffer = WIN_CreateWindowFramebuffer;
device->UpdateWindowFramebuffer = WIN_UpdateWindowFramebuffer;
device->DestroyWindowFramebuffer = WIN_DestroyWindowFramebuffer;
device->OnWindowEnter = WIN_OnWindowEnter;
device->shape_driver.CreateShaper = Win32_CreateShaper;
device->shape_driver.SetWindowShape = Win32_SetWindowShape;
device->shape_driver.ResizeWindowShape = Win32_ResizeWindowShape;
#if SDL_VIDEO_OPENGL_WGL
device->GL_LoadLibrary = WIN_GL_LoadLibrary;
device->GL_GetProcAddress = WIN_GL_GetProcAddress;
device->GL_UnloadLibrary = WIN_GL_UnloadLibrary;
device->GL_CreateContext = WIN_GL_CreateContext;
device->GL_MakeCurrent = WIN_GL_MakeCurrent;
device->GL_SetSwapInterval = WIN_GL_SetSwapInterval;
device->GL_GetSwapInterval = WIN_GL_GetSwapInterval;
device->GL_SwapWindow = WIN_GL_SwapWindow;
device->GL_DeleteContext = WIN_GL_DeleteContext;
#endif
device->StartTextInput = WIN_StartTextInput;
device->StopTextInput = WIN_StopTextInput;
device->SetTextInputRect = WIN_SetTextInputRect;
device->SetClipboardText = WIN_SetClipboardText;
device->GetClipboardText = WIN_GetClipboardText;
device->HasClipboardText = WIN_HasClipboardText;
device->free = WIN_DeleteDevice;
return device;
}
从上文中可以看出，“Windows视频驱动”初始化之后，调用该SDL_VideoDevice的CreateWindow()实际上就等同于调用WIN_CreateWindow()这个函数。因此，我们来看一下WIN_CreateWindow()这个函数的定义（位于video\windows\SDL_windowswindow.c）。
int WIN_CreateWindow(_THIS, SDL_Window * window)
{
HWND hwnd;
RECT rect;
DWORD style = STYLE_BASIC;
int x, y;
int w, h;
style |= GetWindowStyle(window);
/* Figure out what the window area will be */
rect.left = window->x;
rect.top = window->y;
rect.right = window->x + window->w;
rect.bottom = window->y + window->h;
AdjustWindowRectEx(&rect, style, FALSE, 0);
x = rect.left;
y = rect.top;
w = (rect.right - rect.left);
h = (rect.bottom - rect.top);
hwnd =
CreateWindow(SDL_Appname, TEXT(""), style, x, y, w, h, NULL, NULL,
SDL_Instance, NULL);
if (!hwnd) {
return WIN_SetError("Couldn‘t create window");
}
WIN_PumpEvents(_this);
if (SetupWindowData(_this, window, hwnd, SDL_TRUE) < 0) {
DestroyWindow(hwnd);
return -1;
}
#if SDL_VIDEO_OPENGL_WGL
/* We need to initialize the extensions before deciding how to create ES profiles */
if (window->flags & SDL_WINDOW_OPENGL) {
WIN_GL_InitExtensions(_this);
}
#endif
#if SDL_VIDEO_OPENGL_ES2
if ((window->flags & SDL_WINDOW_OPENGL) &&
_this->gl_config.profile_mask == SDL_GL_CONTEXT_PROFILE_ES
#if SDL_VIDEO_OPENGL_WGL
&& (!_this->gl_data || !_this->gl_data->HAS_WGL_EXT_create_context_es2_profile)
#endif
) {
#if SDL_VIDEO_OPENGL_EGL
if (WIN_GLES_SetupWindow(_this, window) < 0) {
WIN_DestroyWindow(_this, window);
return -1;
}
#else
return SDL_SetError("Could not create GLES window surface (no EGL support available)");
#endif /* SDL_VIDEO_OPENGL_EGL */
} else
#endif /* SDL_VIDEO_OPENGL_ES2 */
#if SDL_VIDEO_OPENGL_WGL
if (window->flags & SDL_WINDOW_OPENGL) {
if (WIN_GL_SetupWindow(_this, window) < 0) {
WIN_DestroyWindow(_this, window);
return -1;
}
}
#endif
return 0;
}
从该函数的代码中我们可以看到很多的Win32的API。最核心的函数只有一个，就是CreateWindow()。正是这个Win32的API最终创建了SDL的窗口。当然，为了创建出来的窗口更“优质”，包含了一些初始化的工作，例如AdjustWindowRectEx()；以及一些收尾工作，例如SetupWindowData()（该函数主要用于设置SDL_Window的参数）。
4. 完成一些收尾工作。例如设置窗口的标题，如果是“全屏模式”则设置全屏显示等等。在这里简单介绍几个函数。
SDL_SetWindowTitle()用于设置窗口的标题，它的代码如下。
void SDL_SetWindowTitle(SDL_Window * window, const char *title)
{
CHECK_WINDOW_MAGIC(window, );
if (title == window->title) {
return;
}
SDL_free(window->title);
if (title && *title) {
window->title = SDL_strdup(title);
} else {
window->title = NULL;
}
if (_this->SetWindowTitle) {
_this->SetWindowTitle(_this, window);
}
}
该函数调用了SDL_VideoDevice的SetWindowTitle()。在“Windows视频驱动”中，实际的执行函数是WIN_SetWindowTitle()。该函数的代码如下。
void WIN_SetWindowTitle(_THIS, SDL_Window * window)
{
HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
LPTSTR title;
if (window->title) {
title = WIN_UTF8ToString(window->title);
} else {
title = NULL;
}
SetWindowText(hwnd, title ? title : TEXT(""));
SDL_free(title);
}
从代码中可以看出，该函数调用了Win32的API函数SetWindowText()设置窗口的标题。
SDL_FinishWindowCreation()完成一些窗口的收尾工作。该函数的代码如下。
static void SDL_FinishWindowCreation(SDL_Window *window, Uint32 flags)
{
window->windowed.x = window->x;
window->windowed.y = window->y;
window->windowed.w = window->w;
window->windowed.h = window->h;
if (flags & SDL_WINDOW_MAXIMIZED) {
SDL_MaximizeWindow(window);
}
if (flags & SDL_WINDOW_MINIMIZED) {
SDL_MinimizeWindow(window);
}
if (flags & SDL_WINDOW_FULLSCREEN) {
SDL_SetWindowFullscreen(window, flags);
}
if (flags & SDL_WINDOW_INPUT_GRABBED) {
SDL_SetWindowGrab(window, SDL_TRUE);
}
if (!(flags & SDL_WINDOW_HIDDEN)) {
SDL_ShowWindow(window);
}
}
从代码中可以看出，如果创建窗口的时候：
指定了“最大化”，则会执行SDL_MaximizeWindow()；
指定了“最小化”，则会执行SDL_MinimizeWindow()；
指定了“全屏”，则会执行SDL_SetWindowFullscreen()；
指定了“抓取”（这个没有试过），则会执行SDL_SetWindowGrab()；
指定了“隐藏”，则会执行SDL_ShowWindow()。
下面分别看一下SDL_MaximizeWindow()，SDL_MinimizeWindow()，SDL_SetWindowFullscreen()，SDL_ShowWindow()的代码。
SDL_MaximizeWindow()代码如下。
void SDL_MaximizeWindow(SDL_Window * window)
{
CHECK_WINDOW_MAGIC(window, );
if (window->flags & SDL_WINDOW_MAXIMIZED) {
return;
}
/* !!! FIXME: should this check if the window is resizable? */
if (_this->MaximizeWindow) {
_this->MaximizeWindow(_this, window);
}
}
从代码中可以看出，SDL_MaximizeWindow()调用了SDL_VideoDevice的MaximizeWindow()函数。在“Windows视频驱动”下，实际上调用了WIN_MaximizeWindow()函数，该函数的定义如下。
void WIN_MaximizeWindow(_THIS, SDL_Window * window)
{
SDL_WindowData *data = (SDL_WindowData *)window->driverdata;
HWND hwnd = data->hwnd;
data->expected_resize = TRUE;
ShowWindow(hwnd, SW_MAXIMIZE);
data->expected_resize = FALSE;
}
从上述代码中可以看出WIN_MaximizeWindow()调用了Win32的API函数ShowWindow()。
SDL_MinimizeWindow()代码如下。
void SDL_MinimizeWindow(SDL_Window * window)
{
CHECK_WINDOW_MAGIC(window, );
if (window->flags & SDL_WINDOW_MINIMIZED) {
return;
}
SDL_UpdateFullscreenMode(window, SDL_FALSE);
if (_this->MinimizeWindow) {
_this->MinimizeWindow(_this, window);
}
}
从代码中可以看出，SDL_MinimizeWindow()调用了SDL_VideoDevice的MinimizeWindow()函数。在“Windows视频驱动”下，实际上调用了WIN_MinimizeWindow()函数，该函数的定义如下。
void WIN_MinimizeWindow(_THIS, SDL_Window * window)
{
HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
ShowWindow(hwnd, SW_MINIMIZE);
}
从上述代码中可以看出WIN_MinimizeWindow()调用了Win32的API函数ShowWindow()。
SDL_SetWindowFullscreen()代码如下。
int SDL_SetWindowFullscreen(SDL_Window * window, Uint32 flags)
{
CHECK_WINDOW_MAGIC(window, -1);
flags &= FULLSCREEN_MASK;
if ( flags == (window->flags & FULLSCREEN_MASK) ) {
return 0;
}
/* clear the previous flags and OR in the new ones */
window->flags &= ~FULLSCREEN_MASK;
window->flags |= flags;
SDL_UpdateFullscreenMode(window, FULLSCREEN_VISIBLE(window));
return 0;
}
从代码中可以看出，SDL_SetWindowFullscreen()调用了SDL_UpdateFullscreenMode()函数，该函数的代码如下。
static void SDL_UpdateFullscreenMode(SDL_Window * window, SDL_bool fullscreen)
{
SDL_VideoDisplay *display;
SDL_Window *other;
#ifdef __MACOSX__
if (Cocoa_SetWindowFullscreenSpace(window, fullscreen)) {
window->last_fullscreen_flags = window->flags;
return;
}
#endif
display = SDL_GetDisplayForWindow(window);
if (fullscreen) {
/* Hide any other fullscreen windows */
if (display->fullscreen_window &&
display->fullscreen_window != window) {
SDL_MinimizeWindow(display->fullscreen_window);
}
}
/* See if anything needs to be done now */
if ((display->fullscreen_window == window) == fullscreen) {
if ((window->last_fullscreen_flags & FULLSCREEN_MASK) == (window->flags & FULLSCREEN_MASK)) {
return;
}
}
/* See if there are any fullscreen windows */
for (other = _this->windows; other; other = other->next) {
SDL_bool setDisplayMode = SDL_FALSE;
if (other == window) {
setDisplayMode = fullscreen;
} else if (FULLSCREEN_VISIBLE(other) &&
SDL_GetDisplayForWindow(other) == display) {
setDisplayMode = SDL_TRUE;
}
if (setDisplayMode) {
SDL_DisplayMode fullscreen_mode;
if (SDL_GetWindowDisplayMode(other, &fullscreen_mode) == 0) {
SDL_bool resized = SDL_TRUE;
if (other->w == fullscreen_mode.w && other->h == fullscreen_mode.h) {
resized = SDL_FALSE;
}
/* only do the mode change if we want exclusive fullscreen */
if ((window->flags & SDL_WINDOW_FULLSCREEN_DESKTOP) != SDL_WINDOW_FULLSCREEN_DESKTOP) {
SDL_SetDisplayModeForDisplay(display, &fullscreen_mode);
} else {
SDL_SetDisplayModeForDisplay(display, NULL);
}
if (_this->SetWindowFullscreen) {
_this->SetWindowFullscreen(_this, other, display, SDL_TRUE);
}
display->fullscreen_window = other;
/* Generate a mode change event here */
if (resized) {
SDL_SendWindowEvent(other, SDL_WINDOWEVENT_RESIZED,
fullscreen_mode.w, fullscreen_mode.h);
} else {
SDL_OnWindowResized(other);
}
SDL_RestoreMousePosition(other);
window->last_fullscreen_flags = window->flags;
return;
}
}
}
/* Nope, restore the desktop mode */
SDL_SetDisplayModeForDisplay(display, NULL);
if (_this->SetWindowFullscreen) {
_this->SetWindowFullscreen(_this, window, display, SDL_FALSE);
}
display->fullscreen_window = NULL;
/* Generate a mode change event here */
SDL_OnWindowResized(window);
/* Restore the cursor position */
SDL_RestoreMousePosition(window);
window->last_fullscreen_flags = window->flags;
}
SDL_UpdateFullscreenMode()代码很长，在这里我们只选择最关键的代码进行分析。SDL_UpdateFullscreenMode()最关键的地方在于它调用了SDL_VideoDevice的SetWindowFullscreen()函数。在“Windows视频驱动”下，实际上调用了WIN_SetWindowFullscreen()函数，该函数的定义如下。
void WIN_SetWindowFullscreen(_THIS, SDL_Window * window, SDL_VideoDisplay * display, SDL_bool fullscreen)
{
SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
HWND hwnd = data->hwnd;
RECT rect;
SDL_Rect bounds;
DWORD style;
HWND top;
BOOL menu;
int x, y;
int w, h;
if (SDL_ShouldAllowTopmost() && (window->flags & (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) == (SDL_WINDOW_FULLSCREEN|SDL_WINDOW_INPUT_FOCUS)) {
top = HWND_TOPMOST;
} else {
top = HWND_NOTOPMOST;
}
style = GetWindowLong(hwnd, GWL_STYLE);
style &= ~STYLE_MASK;
style |= GetWindowStyle(window);
WIN_GetDisplayBounds(_this, display, &bounds);
if (fullscreen) {
x = bounds.x;
y = bounds.y;
w = bounds.w;
h = bounds.h;
} else {
rect.left = 0;
rect.top = 0;
rect.right = window->windowed.w;
rect.bottom = window->windowed.h;
menu = (style & WS_CHILDWINDOW) ? FALSE : (GetMenu(hwnd) != NULL);
AdjustWindowRectEx(&rect, style, menu, 0);
w = (rect.right - rect.left);
h = (rect.bottom - rect.top);
x = window->windowed.x + rect.left;
y = window->windowed.y + rect.top;
}
SetWindowLong(hwnd, GWL_STYLE, style);
data->expected_resize = TRUE;
SetWindowPos(hwnd, top, x, y, w, h, SWP_NOCOPYBITS | SWP_NOACTIVATE);
data->expected_resize = FALSE;
}
从代码中可以看出，该函数通过WIN_GetDisplayBounds()获得屏幕的尺寸，然后通过SetWindowPos()函数设置全屏窗口的大小和位置。
SDL_ShowWindow()的代码如下。
void SDL_ShowWindow(SDL_Window * window)
{
CHECK_WINDOW_MAGIC(window, );
if (window->flags & SDL_WINDOW_SHOWN) {
return;
}
if (_this->ShowWindow) {
_this->ShowWindow(_this, window);
}
SDL_SendWindowEvent(window, SDL_WINDOWEVENT_SHOWN, 0, 0);
}
SDL_ShowWindow ()调用了SDL_VideoDevice的ShowWindow()函数。在“Windows视频驱动”下，实际上调用了WIN_ShowWindow()函数，该函数的定义如下。
void WIN_ShowWindow(_THIS, SDL_Window * window)
{
HWND hwnd = ((SDL_WindowData *) window->driverdata)->hwnd;
ShowWindow(hwnd, SW_SHOW);
}
该函数比较简单，直接调用了Win32中的ShowWindow()方法。
函数调用关系图
SDL_ CreateWindow ()关键函数的调用关系可以用下图表示。上面的函数调用关系图本来是一张高清大图，但是由于博客对图片尺寸有限制，因而显得不太清晰。相册里面上传了一份原始的大图片：
http://my.csdn.net/leixiaohua1020/album/detail/1793195