SDL2源代码分析2：窗口（SDL_Window）

迈不过友情╰ 2022-08-20 05:23 191阅读 0赞

=====================================================

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_1_SDL_Init]

[SDL2源代码分析2：窗口（SDL\_Window）][SDL2_2_SDL_Window]

[SDL2源代码分析3：渲染器（SDL\_Renderer）][SDL2_3_SDL_Renderer]

[SDL2源代码分析4：纹理（SDL\_Texture）][SDL2_4_SDL_Texture]

[SDL2源代码分析5：更新纹理（SDL\_UpdateTexture()）][SDL2_5_SDL_UpdateTexture]

[SDL2源代码分析6：复制到渲染器（SDL\_RenderCopy()）][SDL2_6_SDL_RenderCopy]

[SDL2源代码分析7：显示（SDL\_RenderPresent()）][SDL2_7_SDL_RenderPresent]

[SDL2源代码分析8：视频显示总结][SDL2_8]

=====================================================

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）。

![SouthEast][]

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：

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  /\*\*
2.   \* \\brief The type used to identify a window
3.   \*
4.   \* \\sa SDL\_CreateWindow()
5.   \* \\sa SDL\_CreateWindowFrom()
6.   \* \\sa SDL\_DestroyWindow()
7.   \* \\sa SDL\_GetWindowData()
8.   \* \\sa SDL\_GetWindowFlags()
9.   \* \\sa SDL\_GetWindowGrab()
10.  \* \\sa SDL\_GetWindowPosition()
11.  \* \\sa SDL\_GetWindowSize()
12.  \* \\sa SDL\_GetWindowTitle()
13.  \* \\sa SDL\_HideWindow()
14.  \* \\sa SDL\_MaximizeWindow()
15.  \* \\sa SDL\_MinimizeWindow()
16.  \* \\sa SDL\_RaiseWindow()
17.  \* \\sa SDL\_RestoreWindow()
18.  \* \\sa SDL\_SetWindowData()
19.  \* \\sa SDL\_SetWindowFullscreen()
20.  \* \\sa SDL\_SetWindowGrab()
21.  \* \\sa SDL\_SetWindowIcon()
22.  \* \\sa SDL\_SetWindowPosition()
23.  \* \\sa SDL\_SetWindowSize()
24.  \* \\sa SDL\_SetWindowBordered()
25.  \* \\sa SDL\_SetWindowTitle()
26.  \* \\sa SDL\_ShowWindow()
27.  \*/
28. **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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  /\* Define the SDL window structure, corresponding to toplevel windows \*/
2.  **struct** SDL\_Window 
3.  \{ 
4.  **const****void** \*magic; 
5.   Uint32 id; 
6.  **char** \*title; 
7.   SDL\_Surface \*icon; 
8.  **int** x, y; 
9.  **int** w, h; 
10. **int** min\_w, min\_h; 
11. **int** max\_w, max\_h; 
12.  Uint32 flags; 
13.  Uint32 last\_fullscreen\_flags; 
14. 
15. 
16. /\* Stored position and size for windowed mode \*/
17.  SDL\_Rect windowed; 
18. 
19. 
20.  SDL\_DisplayMode fullscreen\_mode; 
21. 
22. 
23. **float** brightness; 
24.  Uint16 \*gamma; 
25.  Uint16 \*saved\_gamma; /\* (just offset into gamma) \*/
26. 
27. 
28.  SDL\_Surface \*surface; 
29.  SDL\_bool surface\_valid; 
30. 
31. 
32.  SDL\_bool is\_destroying; 
33. 
34. 
35.  SDL\_WindowShaper \*shaper; 
36. 
37. 
38.  SDL\_WindowUserData \*data; 
39. 
40. 
41. **void** \*driverdata; 
42. 
43. 
44.  SDL\_Window \*prev; 
45.  SDL\_Window \*next; 
46. \};

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  SDL\_Window \* SDLCALL SDL\_CreateWindow(**const****char** \*title, 
2.  **int** x, **int** y, **int** w, 
3.  **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。

[![SouthEast 1][]][SouthEast 1 1]

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][SouthEast 1 1]

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  SDL\_Window \* SDL\_CreateWindow(**const****char** \*title, **int** x, **int** y, **int** w, **int** h, Uint32 flags) 
2.  \{ 
3.   SDL\_Window \*window; 
4.  **const****char** \*hint; 
5.  
6.  
7.  **if** (!\_this) \{ 
8.  /\* Initialize the video system if needed \*/
9.  **if** (SDL\_VideoInit(NULL) < 0) \{ 
10. **return** NULL; 
11.  \} 
12.  \} 
13. 
14. 
15. /\* Some platforms can't create zero-sized windows \*/
16. **if** (w < 1) \{ 
17.  w = 1; 
18.  \} 
19. **if** (h < 1) \{ 
20.  h = 1; 
21.  \} 
22. 
23. 
24. /\* Some platforms have OpenGL enabled by default \*/
25. \#if (SDL\_VIDEO\_OPENGL && \_\_MACOSX\_\_) || \_\_IPHONEOS\_\_ || \_\_ANDROID\_\_
26.  flags |= SDL\_WINDOW\_OPENGL; 
27. \#endif
28. **if** (flags & SDL\_WINDOW\_OPENGL) \{ 
29. **if** (!\_this->GL\_CreateContext) \{ 
30.  SDL\_SetError("No OpenGL support in video driver"); 
31. **return** NULL; 
32.  \} 
33. **if** (SDL\_GL\_LoadLibrary(NULL) < 0) \{ 
34. **return** NULL; 
35.  \} 
36.  \} 
37. 
38. 
39. /\* Unless the user has specified the high-DPI disabling hint, respect the
40.  \* SDL\_WINDOW\_ALLOW\_HIGHDPI flag.
41.  \*/
42. **if** (flags & SDL\_WINDOW\_ALLOW\_HIGHDPI) \{ 
43.  hint = SDL\_GetHint(SDL\_HINT\_VIDEO\_HIGHDPI\_DISABLED); 
44. **if** (hint && SDL\_atoi(hint) > 0) \{ 
45.  flags &= ~SDL\_WINDOW\_ALLOW\_HIGHDPI; 
46.  \} 
47.  \} 
48. 
49. 
50.  window = (SDL\_Window \*)SDL\_calloc(1, **sizeof**(\*window)); 
51. **if** (!window) \{ 
52.  SDL\_OutOfMemory(); 
53. **return** NULL; 
54.  \} 
55.  window->magic = &\_this->window\_magic; 
56.  window->id = \_this->next\_object\_id++; 
57.  window->x = x; 
58.  window->y = y; 
59.  window->w = w; 
60.  window->h = h; 
61. **if** (SDL\_WINDOWPOS\_ISUNDEFINED(x) || SDL\_WINDOWPOS\_ISUNDEFINED(y) || 
62.  SDL\_WINDOWPOS\_ISCENTERED(x) || SDL\_WINDOWPOS\_ISCENTERED(y)) \{ 
63.  SDL\_VideoDisplay \*display = SDL\_GetDisplayForWindow(window); 
64. **int** displayIndex; 
65.  SDL\_Rect bounds; 
66. 
67. 
68.  displayIndex = SDL\_GetIndexOfDisplay(display); 
69.  SDL\_GetDisplayBounds(displayIndex, &bounds); 
70. **if** (SDL\_WINDOWPOS\_ISUNDEFINED(x) || SDL\_WINDOWPOS\_ISCENTERED(x)) \{ 
71.  window->x = bounds.x + (bounds.w - w) / 2; 
72.  \} 
73. **if** (SDL\_WINDOWPOS\_ISUNDEFINED(y) || SDL\_WINDOWPOS\_ISCENTERED(y)) \{ 
74.  window->y = bounds.y + (bounds.h - h) / 2; 
75.  \} 
76.  \} 
77.  window->flags = ((flags & CREATE\_FLAGS) | SDL\_WINDOW\_HIDDEN); 
78.  window->last\_fullscreen\_flags = window->flags; 
79.  window->brightness = 1.0f; 
80.  window->next = \_this->windows; 
81.  window->is\_destroying = SDL\_FALSE; 
82. 
83. 
84. **if** (\_this->windows) \{ 
85.  \_this->windows->prev = window; 
86.  \} 
87.  \_this->windows = window; 
88. 
89. 
90. **if** (\_this->CreateWindow && \_this->CreateWindow(\_this, window) < 0) \{ 
91.  SDL\_DestroyWindow(window); 
92. **return** NULL; 
93.  \} 
94. 
95. 
96. **if** (title) \{ 
97.  SDL\_SetWindowTitle(window, title); 
98.  \} 
99.  SDL\_FinishWindowCreation(window, flags); 
100. 
101. 
102. /\* If the window was created fullscreen, make sure the mode code matches \*/
103.  SDL\_UpdateFullscreenMode(window, FULLSCREEN\_VISIBLE(window)); 
104. 
105. 
106. **return** window; 
107. \}

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：

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  \#define memset SDL\_memset
2.  \#define memcpy SDL\_memcpy
3.  \#define malloc SDL\_malloc
4.  \#define calloc SDL\_calloc
5.  \#define realloc SDL\_realloc
6.  \#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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **static** SDL\_VideoDevice \*WIN\_CreateDevice(**int** devindex) 
2.  \{ 
3.   SDL\_VideoDevice \*device; 
4.   SDL\_VideoData \*data; 
5.  
6.  
7.   SDL\_RegisterApp(NULL, 0, NULL); 
8.  
9.  
10. /\* Initialize all variables that we clean on shutdown \*/
11.  device = (SDL\_VideoDevice \*) SDL\_calloc(1, **sizeof**(SDL\_VideoDevice)); 
12. **if** (device) \{ 
13.  data = (**struct** SDL\_VideoData \*) SDL\_calloc(1, **sizeof**(SDL\_VideoData)); 
14.  \} **else** \{ 
15.  data = NULL; 
16.  \} 
17. **if** (!data) \{ 
18.  SDL\_free(device); 
19.  SDL\_OutOfMemory(); 
20. **return** NULL; 
21.  \} 
22.  device->driverdata = data; 
23. 
24. 
25.  data->userDLL = SDL\_LoadObject("USER32.DLL"); 
26. **if** (data->userDLL) \{ 
27.  data->CloseTouchInputHandle = (**BOOL** (WINAPI \*)( HTOUCHINPUT )) SDL\_LoadFunction(data->userDLL, "CloseTouchInputHandle"); 
28.  data->GetTouchInputInfo = (**BOOL** (WINAPI \*)( HTOUCHINPUT, **UINT**, PTOUCHINPUT, **int** )) SDL\_LoadFunction(data->userDLL, "GetTouchInputInfo"); 
29.  data->RegisterTouchWindow = (**BOOL** (WINAPI \*)( **HWND**, **ULONG** )) SDL\_LoadFunction(data->userDLL, "RegisterTouchWindow"); 
30.  \} 
31. 
32. 
33. /\* Set the function pointers \*/
34.  device->VideoInit = WIN\_VideoInit; 
35.  device->VideoQuit = WIN\_VideoQuit; 
36.  device->GetDisplayBounds = WIN\_GetDisplayBounds; 
37.  device->GetDisplayModes = WIN\_GetDisplayModes; 
38.  device->SetDisplayMode = WIN\_SetDisplayMode; 
39.  device->PumpEvents = WIN\_PumpEvents; 
40. 
41. 
42. \#undef CreateWindow
43.  device->CreateWindow = WIN\_CreateWindow; 
44.  device->CreateWindowFrom = WIN\_CreateWindowFrom; 
45.  device->SetWindowTitle = WIN\_SetWindowTitle; 
46.  device->SetWindowIcon = WIN\_SetWindowIcon; 
47.  device->SetWindowPosition = WIN\_SetWindowPosition; 
48.  device->SetWindowSize = WIN\_SetWindowSize; 
49.  device->ShowWindow = WIN\_ShowWindow; 
50.  device->HideWindow = WIN\_HideWindow; 
51.  device->RaiseWindow = WIN\_RaiseWindow; 
52.  device->MaximizeWindow = WIN\_MaximizeWindow; 
53.  device->MinimizeWindow = WIN\_MinimizeWindow; 
54.  device->RestoreWindow = WIN\_RestoreWindow; 
55.  device->SetWindowBordered = WIN\_SetWindowBordered; 
56.  device->SetWindowFullscreen = WIN\_SetWindowFullscreen; 
57.  device->SetWindowGammaRamp = WIN\_SetWindowGammaRamp; 
58.  device->GetWindowGammaRamp = WIN\_GetWindowGammaRamp; 
59.  device->SetWindowGrab = WIN\_SetWindowGrab; 
60.  device->DestroyWindow = WIN\_DestroyWindow; 
61.  device->GetWindowWMInfo = WIN\_GetWindowWMInfo; 
62.  device->CreateWindowFramebuffer = WIN\_CreateWindowFramebuffer; 
63.  device->UpdateWindowFramebuffer = WIN\_UpdateWindowFramebuffer; 
64.  device->DestroyWindowFramebuffer = WIN\_DestroyWindowFramebuffer; 
65.  device->OnWindowEnter = WIN\_OnWindowEnter; 
66. 
67. 
68.  device->shape\_driver.CreateShaper = Win32\_CreateShaper; 
69.  device->shape\_driver.SetWindowShape = Win32\_SetWindowShape; 
70.  device->shape\_driver.ResizeWindowShape = Win32\_ResizeWindowShape; 
71. 
72. 
73. \#if SDL\_VIDEO\_OPENGL\_WGL
74.  device->GL\_LoadLibrary = WIN\_GL\_LoadLibrary; 
75.  device->GL\_GetProcAddress = WIN\_GL\_GetProcAddress; 
76.  device->GL\_UnloadLibrary = WIN\_GL\_UnloadLibrary; 
77.  device->GL\_CreateContext = WIN\_GL\_CreateContext; 
78.  device->GL\_MakeCurrent = WIN\_GL\_MakeCurrent; 
79.  device->GL\_SetSwapInterval = WIN\_GL\_SetSwapInterval; 
80.  device->GL\_GetSwapInterval = WIN\_GL\_GetSwapInterval; 
81.  device->GL\_SwapWindow = WIN\_GL\_SwapWindow; 
82.  device->GL\_DeleteContext = WIN\_GL\_DeleteContext; 
83. \#endif
84.  device->StartTextInput = WIN\_StartTextInput; 
85.  device->StopTextInput = WIN\_StopTextInput; 
86.  device->SetTextInputRect = WIN\_SetTextInputRect; 
87. 
88. 
89.  device->SetClipboardText = WIN\_SetClipboardText; 
90.  device->GetClipboardText = WIN\_GetClipboardText; 
91.  device->HasClipboardText = WIN\_HasClipboardText; 
92. 
93. 
94.  device->free = WIN\_DeleteDevice; 
95. 
96. 
97. **return** device; 
98. \}

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）。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **int** WIN\_CreateWindow(\_THIS, SDL\_Window \* window) 
2.  \{ 
3.  **HWND** hwnd; 
4.   RECT rect; 
5.  **DWORD** style = STYLE\_BASIC; 
6.  **int** x, y; 
7.  **int** w, h; 
8.  
9.  
10.  style |= GetWindowStyle(window); 
11. 
12. 
13. /\* Figure out what the window area will be \*/
14.  rect.left = window->x; 
15.  rect.top = window->y; 
16.  rect.right = window->x + window->w; 
17.  rect.bottom = window->y + window->h; 
18.  AdjustWindowRectEx(&rect, style, FALSE, 0); 
19.  x = rect.left; 
20.  y = rect.top; 
21.  w = (rect.right - rect.left); 
22.  h = (rect.bottom - rect.top); 
23. 
24. 
25.  hwnd = 
26.  CreateWindow(SDL\_Appname, TEXT(""), style, x, y, w, h, NULL, NULL, 
27.  SDL\_Instance, NULL); 
28. **if** (!hwnd) \{ 
29. **return** WIN\_SetError("Couldn't create window"); 
30.  \} 
31. 
32. 
33.  WIN\_PumpEvents(\_this); 
34. 
35. 
36. **if** (SetupWindowData(\_this, window, hwnd, SDL\_TRUE) < 0) \{ 
37.  DestroyWindow(hwnd); 
38. **return** \-1; 
39.  \} 
40. 
41. 
42. \#if SDL\_VIDEO\_OPENGL\_WGL
43. /\* We need to initialize the extensions before deciding how to create ES profiles \*/
44. **if** (window->flags & SDL\_WINDOW\_OPENGL) \{ 
45.  WIN\_GL\_InitExtensions(\_this); 
46.  \} 
47. \#endif
48. 
49. 
50. \#if SDL\_VIDEO\_OPENGL\_ES2
51. **if** ((window->flags & SDL\_WINDOW\_OPENGL) && 
52.  \_this->gl\_config.profile\_mask == SDL\_GL\_CONTEXT\_PROFILE\_ES 
53. \#if SDL\_VIDEO\_OPENGL\_WGL 
54.  && (!\_this->gl\_data || !\_this->gl\_data->HAS\_WGL\_EXT\_create\_context\_es2\_profile) 
55. \#endif 
56.  ) \{ 
57. \#if SDL\_VIDEO\_OPENGL\_EGL 
58. **if** (WIN\_GLES\_SetupWindow(\_this, window) < 0) \{ 
59.  WIN\_DestroyWindow(\_this, window); 
60. **return** \-1; 
61.  \} 
62. \#else
63. **return** SDL\_SetError("Could not create GLES window surface (no EGL support available)"); 
64. \#endif /\* SDL\_VIDEO\_OPENGL\_EGL \*/
65.  \} **else**
66. \#endif /\* SDL\_VIDEO\_OPENGL\_ES2 \*/
67. 
68. 
69. \#if SDL\_VIDEO\_OPENGL\_WGL
70. **if** (window->flags & SDL\_WINDOW\_OPENGL) \{ 
71. **if** (WIN\_GL\_SetupWindow(\_this, window) < 0) \{ 
72.  WIN\_DestroyWindow(\_this, window); 
73. **return** \-1; 
74.  \} 
75.  \} 
76. \#endif
77. 
78. 
79. **return** 0; 
80. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** SDL\_SetWindowTitle(SDL\_Window \* window, **const****char** \*title) 
2.  \{ 
3.   CHECK\_WINDOW\_MAGIC(window, ); 
4.  
5.  
6.  **if** (title == window->title) \{ 
7.  **return**; 
8.   \} 
9.   SDL\_free(window->title); 
10. **if** (title && \*title) \{ 
11.  window->title = SDL\_strdup(title); 
12.  \} **else** \{ 
13.  window->title = NULL; 
14.  \} 
15. 
16. 
17. **if** (\_this->SetWindowTitle) \{ 
18.  \_this->SetWindowTitle(\_this, window); 
19.  \} 
20. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** WIN\_SetWindowTitle(\_THIS, SDL\_Window \* window) 
2.  \{ 
3.  **HWND** hwnd = ((SDL\_WindowData \*) window->driverdata)->hwnd; 
4.  **LPTSTR** title; 
5.  
6.  
7.  **if** (window->title) \{ 
8.   title = WIN\_UTF8ToString(window->title); 
9.   \} **else** \{ 
10.  title = NULL; 
11.  \} 
12.  SetWindowText(hwnd, title ? title : TEXT("")); 
13.  SDL\_free(title); 
14. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **static****void** SDL\_FinishWindowCreation(SDL\_Window \*window, Uint32 flags) 
2.  \{ 
3.   window->windowed.x = window->x; 
4.   window->windowed.y = window->y; 
5.   window->windowed.w = window->w; 
6.   window->windowed.h = window->h; 
7.  
8.  
9.  **if** (flags & SDL\_WINDOW\_MAXIMIZED) \{ 
10.  SDL\_MaximizeWindow(window); 
11.  \} 
12. **if** (flags & SDL\_WINDOW\_MINIMIZED) \{ 
13.  SDL\_MinimizeWindow(window); 
14.  \} 
15. **if** (flags & SDL\_WINDOW\_FULLSCREEN) \{ 
16.  SDL\_SetWindowFullscreen(window, flags); 
17.  \} 
18. **if** (flags & SDL\_WINDOW\_INPUT\_GRABBED) \{ 
19.  SDL\_SetWindowGrab(window, SDL\_TRUE); 
20.  \} 
21. **if** (!(flags & SDL\_WINDOW\_HIDDEN)) \{ 
22.  SDL\_ShowWindow(window); 
23.  \} 
24. \}

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。**

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** SDL\_MaximizeWindow(SDL\_Window \* window) 
2.  \{ 
3.   CHECK\_WINDOW\_MAGIC(window, ); 
4.  
5.  
6.  **if** (window->flags & SDL\_WINDOW\_MAXIMIZED) \{ 
7.  **return**; 
8.   \} 
9.  
10. 
11. /\* !!! FIXME: should this check if the window is resizable? \*/
12. 
13. 
14. **if** (\_this->MaximizeWindow) \{ 
15.  \_this->MaximizeWindow(\_this, window); 
16.  \} 
17. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** WIN\_MaximizeWindow(\_THIS, SDL\_Window \* window) 
2.  \{ 
3.   SDL\_WindowData \*data = (SDL\_WindowData \*)window->driverdata; 
4.  **HWND** hwnd = data->hwnd; 
5.   data->expected\_resize = TRUE; 
6.   ShowWindow(hwnd, SW\_MAXIMIZE); 
7.   data->expected\_resize = FALSE; 
8.  \}

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。**

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** SDL\_MinimizeWindow(SDL\_Window \* window) 
2.  \{ 
3.   CHECK\_WINDOW\_MAGIC(window, ); 
4.  
5.  
6.  **if** (window->flags & SDL\_WINDOW\_MINIMIZED) \{ 
7.  **return**; 
8.   \} 
9.  
10. 
11.  SDL\_UpdateFullscreenMode(window, SDL\_FALSE); 
12. 
13. 
14. **if** (\_this->MinimizeWindow) \{ 
15.  \_this->MinimizeWindow(\_this, window); 
16.  \} 
17. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** WIN\_MinimizeWindow(\_THIS, SDL\_Window \* window) 
2.  \{ 
3.  **HWND** hwnd = ((SDL\_WindowData \*) window->driverdata)->hwnd; 
4.   ShowWindow(hwnd, SW\_MINIMIZE); 
5.  \}

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。**

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **int** SDL\_SetWindowFullscreen(SDL\_Window \* window, Uint32 flags) 
2.  \{ 
3.   CHECK\_WINDOW\_MAGIC(window, -1); 
4.  
5.  
6.   flags &= FULLSCREEN\_MASK; 
7.  
8.  
9.  **if** ( flags == (window->flags & FULLSCREEN\_MASK) ) \{ 
10. **return** 0; 
11.  \} 
12. 
13. 
14. /\* clear the previous flags and OR in the new ones \*/
15.  window->flags &= ~FULLSCREEN\_MASK; 
16.  window->flags |= flags; 
17. 
18. 
19.  SDL\_UpdateFullscreenMode(window, FULLSCREEN\_VISIBLE(window)); 
20. 
21. 
22. **return** 0; 
23. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **static****void** SDL\_UpdateFullscreenMode(SDL\_Window \* window, SDL\_bool fullscreen) 
2.  \{ 
3.   SDL\_VideoDisplay \*display; 
4.   SDL\_Window \*other; 
5.  
6.  
7.  \#ifdef \_\_MACOSX\_\_
8.  **if** (Cocoa\_SetWindowFullscreenSpace(window, fullscreen)) \{ 
9.   window->last\_fullscreen\_flags = window->flags; 
10. **return**; 
11.  \} 
12. \#endif
13. 
14. 
15.  display = SDL\_GetDisplayForWindow(window); 
16. 
17. 
18. **if** (fullscreen) \{ 
19. /\* Hide any other fullscreen windows \*/
20. **if** (display->fullscreen\_window && 
21.  display->fullscreen\_window != window) \{ 
22.  SDL\_MinimizeWindow(display->fullscreen\_window); 
23.  \} 
24.  \} 
25. 
26. 
27. /\* See if anything needs to be done now \*/
28. **if** ((display->fullscreen\_window == window) == fullscreen) \{ 
29. **if** ((window->last\_fullscreen\_flags & FULLSCREEN\_MASK) == (window->flags & FULLSCREEN\_MASK)) \{ 
30. **return**; 
31.  \} 
32.  \} 
33. 
34. 
35. /\* See if there are any fullscreen windows \*/
36. **for** (other = \_this->windows; other; other = other->next) \{ 
37.  SDL\_bool setDisplayMode = SDL\_FALSE; 
38. 
39. 
40. **if** (other == window) \{ 
41.  setDisplayMode = fullscreen; 
42.  \} **else****if** (FULLSCREEN\_VISIBLE(other) && 
43.  SDL\_GetDisplayForWindow(other) == display) \{ 
44.  setDisplayMode = SDL\_TRUE; 
45.  \} 
46. 
47. 
48. **if** (setDisplayMode) \{ 
49.  SDL\_DisplayMode fullscreen\_mode; 
50. 
51. 
52. **if** (SDL\_GetWindowDisplayMode(other, &fullscreen\_mode) == 0) \{ 
53.  SDL\_bool resized = SDL\_TRUE; 
54. 
55. 
56. **if** (other->w == fullscreen\_mode.w && other->h == fullscreen\_mode.h) \{ 
57.  resized = SDL\_FALSE; 
58.  \} 
59. 
60. 
61. /\* only do the mode change if we want exclusive fullscreen \*/
62. **if** ((window->flags & SDL\_WINDOW\_FULLSCREEN\_DESKTOP) != SDL\_WINDOW\_FULLSCREEN\_DESKTOP) \{ 
63.  SDL\_SetDisplayModeForDisplay(display, &fullscreen\_mode); 
64.  \} **else** \{ 
65.  SDL\_SetDisplayModeForDisplay(display, NULL); 
66.  \} 
67. 
68. 
69. **if** (\_this->SetWindowFullscreen) \{ 
70.  \_this->SetWindowFullscreen(\_this, other, display, SDL\_TRUE); 
71.  \} 
72.  display->fullscreen\_window = other; 
73. 
74. 
75. /\* Generate a mode change event here \*/
76. **if** (resized) \{ 
77.  SDL\_SendWindowEvent(other, SDL\_WINDOWEVENT\_RESIZED, 
78.  fullscreen\_mode.w, fullscreen\_mode.h); 
79.  \} **else** \{ 
80.  SDL\_OnWindowResized(other); 
81.  \} 
82. 
83. 
84.  SDL\_RestoreMousePosition(other); 
85. 
86. 
87.  window->last\_fullscreen\_flags = window->flags; 
88. **return**; 
89.  \} 
90.  \} 
91.  \} 
92. 
93. 
94. /\* Nope, restore the desktop mode \*/
95.  SDL\_SetDisplayModeForDisplay(display, NULL); 
96. 
97. 
98. **if** (\_this->SetWindowFullscreen) \{ 
99.  \_this->SetWindowFullscreen(\_this, window, display, SDL\_FALSE); 
100.  \} 
101.  display->fullscreen\_window = NULL; 
102. 
103. 
104. /\* Generate a mode change event here \*/
105.  SDL\_OnWindowResized(window); 
106. 
107. 
108. /\* Restore the cursor position \*/
109.  SDL\_RestoreMousePosition(window); 
110. 
111. 
112.  window->last\_fullscreen\_flags = window->flags; 
113. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** WIN\_SetWindowFullscreen(\_THIS, SDL\_Window \* window, SDL\_VideoDisplay \* display, SDL\_bool fullscreen) 
2.  \{ 
3.   SDL\_WindowData \*data = (SDL\_WindowData \*) window->driverdata; 
4.  **HWND** hwnd = data->hwnd; 
5.   RECT rect; 
6.   SDL\_Rect bounds; 
7.  **DWORD** style; 
8.  **HWND** top; 
9.  **BOOL** menu; 
10. **int** x, y; 
11. **int** w, h; 
12. 
13. 
14. **if** (SDL\_ShouldAllowTopmost() && (window->flags & (SDL\_WINDOW\_FULLSCREEN|SDL\_WINDOW\_INPUT\_FOCUS)) == (SDL\_WINDOW\_FULLSCREEN|SDL\_WINDOW\_INPUT\_FOCUS)) \{ 
15.  top = HWND\_TOPMOST; 
16.  \} **else** \{ 
17.  top = HWND\_NOTOPMOST; 
18.  \} 
19. 
20. 
21.  style = GetWindowLong(hwnd, GWL\_STYLE); 
22.  style &= ~STYLE\_MASK; 
23.  style |= GetWindowStyle(window); 
24. 
25. 
26.  WIN\_GetDisplayBounds(\_this, display, &bounds); 
27. 
28. 
29. **if** (fullscreen) \{ 
30.  x = bounds.x; 
31.  y = bounds.y; 
32.  w = bounds.w; 
33.  h = bounds.h; 
34.  \} **else** \{ 
35.  rect.left = 0; 
36.  rect.top = 0; 
37.  rect.right = window->windowed.w; 
38.  rect.bottom = window->windowed.h; 
39.  menu = (style & WS\_CHILDWINDOW) ? FALSE : (GetMenu(hwnd) != NULL); 
40.  AdjustWindowRectEx(&rect, style, menu, 0); 
41.  w = (rect.right - rect.left); 
42.  h = (rect.bottom - rect.top); 
43.  x = window->windowed.x + rect.left; 
44.  y = window->windowed.y + rect.top; 
45.  \} 
46.  SetWindowLong(hwnd, GWL\_STYLE, style); 
47.  data->expected\_resize = TRUE; 
48.  SetWindowPos(hwnd, top, x, y, w, h, SWP\_NOCOPYBITS | SWP\_NOACTIVATE); 
49.  data->expected\_resize = FALSE; 
50. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** SDL\_ShowWindow(SDL\_Window \* window) 
2.  \{ 
3.   CHECK\_WINDOW\_MAGIC(window, ); 
4.  
5.  
6.  **if** (window->flags & SDL\_WINDOW\_SHOWN) \{ 
7.  **return**; 
8.   \} 
9.  
10. 
11. **if** (\_this->ShowWindow) \{ 
12.  \_this->ShowWindow(\_this, window); 
13.  \} 
14.  SDL\_SendWindowEvent(window, SDL\_WINDOWEVENT\_SHOWN, 0, 0); 
15. \}

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。

**\[cpp\]** [view plain][] [copy][view plain]

[![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void** WIN\_ShowWindow(\_THIS, SDL\_Window \* window) 
2.  \{ 
3.  **HWND** hwnd = ((SDL\_WindowData \*) window->driverdata)->hwnd; 
4.   ShowWindow(hwnd, SW\_SHOW); 
5.  \}

该函数比较简单，直接调用了Win32中的ShowWindow()方法。

[SDL2_1_SDL_Init]: http://blog.csdn.net/leixiaohua1020/article/details/40680907
[SDL2_2_SDL_Window]: http://blog.csdn.net/leixiaohua1020/article/details/40701203
[SDL2_3_SDL_Renderer]: http://blog.csdn.net/leixiaohua1020/article/details/40723085
[SDL2_4_SDL_Texture]: http://blog.csdn.net/leixiaohua1020/article/details/40743061
[SDL2_5_SDL_UpdateTexture]: http://blog.csdn.net/leixiaohua1020/article/details/40876089
[SDL2_6_SDL_RenderCopy]: http://blog.csdn.net/leixiaohua1020/article/details/40895593
[SDL2_7_SDL_RenderPresent]: http://blog.csdn.net/leixiaohua1020/article/details/40895797
[SDL2_8]: http://blog.csdn.net/leixiaohua1020/article/details/41207787
[SouthEast]: /images/20220731/edfbe5db504242379d047b46996cfd90.png
[view plain]: http://blog.csdn.net/leixiaohua1020/article/details/40701203#
[CODE]: https://code.csdn.net/assets/CODE_ico.png
[CODE_CODE]: https://code.csdn.net/snippets/505697
[ico_fork.svg]: https://code.csdn.net/assets/ico_fork.svg
[ico_fork.svg 1]: https://code.csdn.net/snippets/505697/fork
[SouthEast 1]: /images/20220731/f9cf654afc46496fa8575d2f0888abe2.png
[SouthEast 1 1]: http://my.csdn.net/leixiaohua1020/album/detail/1793195