SDL2源代码分析2：窗口（SDL

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SDL源代码分析系列文章列表：

SDL2源代码分析1：初始化（SDL_Init()）

SDL2源代码分析2：窗口（SDL_Window）

SDL2源代码分析3：渲染器（SDL_Renderer）

SDL2源代码分析4：纹理（SDL_Texture）

SDL2源代码分析5：更新纹理（SDL_UpdateTexture()）

SDL2源代码分析6：复制到渲染器（SDL_RenderCopy()）

SDL2源代码分析7：显示（SDL_RenderPresent()）

SDL2源代码分析8：视频显示总结

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上一篇文章分析了SDL的初始化函数SDL_Init()。这篇文章继续分析SDL的源代码。本文分析SDL的窗口（SDL_Window）。

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()的原型如下。

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。

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

打开上述相册里面的图片，右键选择“另存为”即可保存原始图片。

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;
#endifif (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 CreateWindowdevice->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_WGLdevice->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;
#endifdevice->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_ES2if ((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;}
#elsereturn 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_WGLif (window->flags & SDL_WINDOW_OPENGL) {if (WIN_GL_SetupWindow(_this, window) < 0) {WIN_DestroyWindow(_this, window);return -1;}}
#endifreturn 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，它的定义如下。

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()。该函数的定义如下。

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。该函数的定义如下。

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()定义如下。

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()定义如下。

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()定义如下。

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，该函数的定义如下。

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;}
#endifdisplay = 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()的定义如下。

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。