一.事件循环
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一个完整的GUI程序，需要处理各种事件，如按键，鼠标，窗口操作等。一般这种程序会设计成一个与底层交互的事件驱动模型。即底层不断发送事件，而在程序用一个循环不断处理各种事件
各个GUI都是采用这样模型来实现，SDL抽象这个模型，采用SDL_event来抽象表示具体的事件，它有如下几种类型。
/** Event enumerations */
typedef enum{
SDL_NOEVENT = 0,/**< Unused (do not remove) */
SDL_ACTIVEEVENT,/**< Application loses/gains visibility
*/
SDL_KEYDOWN,/**< Keys pressed */
SDL_KEYUP,/**< Keys released */
SDL_MOUSEMOTION,/**< Mouse moved */
SDL_MOUSEBUTTONDOWN,/**< Mouse button pressed */
SDL_MOUSEBUTTONUP,/**< Mouse button released */
SDL_JOYAXISMOTION,/**< Joystick axis motion */
SDL_JOYBALLMOTION,/**< Joystick trackball motion */
SDL_JOYHATMOTION,/**< Joystick hat position change */
SDL_JOYBUTTONDOWN,/**< Joystick button pressed */
SDL_JOYBUTTONUP,/**< Joystick button released */
SDL_QUIT,/**< User-requested quit */
SDL_SYSWMEVENT,/**< System specific event */
SDL_EVENT_RESERVEDA,/**< Reserved for future use.. */
SDL_EVENT_RESERVEDB,/**< Reserved for future use.. */
SDL_VIDEORESIZE,/**< User resized video mode */
SDL_VIDEOEXPOSE,/**< Screen needs to be redrawn */
SDL_EVENT_RESERVED2,/**< Reserved for future use.. */
SDL_EVENT_RESERVED3,/**< Reserved for future use.. */
SDL_EVENT_RESERVED4,/**< Reserved for future use.. */
SDL_EVENT_RESERVED5,/**< Reserved for future use.. */
SDL_EVENT_RESERVED6,/**< Reserved for future use.. */
SDL_EVENT_RESERVED7,/**< Reserved for future use.. */ /** Events SDL_USEREVENT through SDL_MAXEVENTS-1 are for your use */
SDL_USEREVENT = 24,
/** This last event is only for bounding internal arrays
* It is the number of bits in the event mask datatype -- Uint32
*/
SDL_NUMEVENTS = 32
} SDL_EventType;
SDL采用 int SDL_PollEvent(SDL_Event *event); 来从底层提取事件。
每一个事件都有一个独立数据结构来定义，但是第一个成员必是一个int type, SDL_Event就是一个各种事件定义的联合
/** General event structure */
typedef union SDL_Event {
Uint8 type;
SDL_ActiveEvent active;
SDL_KeyboardEvent key;
SDL_MouseMotionEvent motion;
SDL_MouseButtonEvent button;
SDL_JoyAxisEvent jaxis;
SDL_JoyBallEvent jball;
SDL_JoyHatEvent jhat;
SDL_JoyButtonEvent jbutton;
SDL_ResizeEvent resize;
SDL_ExposeEvent expose;
SDL_QuitEvent quit;
SDL_UserEvent user;
SDL_SysWMEvent syswm;
} SDL_Event;
而象常用的事件有，退出事件（当你点击窗口关闭键，就会触发此事件）
typedef struct SDL_QuitEvent {
Uint8 type;/**< SDL_QUIT */
} SDL_QuitEvent;
按键处理事件
/** Keyboard event structure */
typedef struct SDL_KeyboardEvent {
Uint8 type;/**< SDL_KEYDOWN or SDL_KEYUP */
Uint8 which;/**< The keyboard device index */
Uint8 state;/**< SDL_PRESSED or SDL_RELEASED */
SDL_keysym keysym;
} SDL_KeyboardEvent;
同步事件
1.2 同步事件处理框架
它将是在主循环完成事件处理，这个循环过程是就是主线程的执行过程
int quit =false;
while( quit ==false)
{
Now we start the main loop.This loop will keep going until the user sets quit to true.//While there's an event to handle
while( SDL_PollEvent(&event ))
{
pe)
{
case SDL_QUIT:
quit =true;
break;
default:
break;
}
}
还有两个不常用的事件函数
SDL_WaitEvent(); //必须等到有一个事件才返回，而SDL_PollEvent 没有事件也立即返回，这样提高系统反应速度。
SDL_PeepEvents(). 是提出事件，但事件本身仍然在事件队列中
1.3异步事件处理。
有时比较复杂的游戏的主循环可能用作其它程序，这时用得上事件过滤器，事件过滤器，在有事件发生调用事件处理回调函数。因此称为异步事件处理.
它调用void SDL_SetEventFilter(SDL_EventFilter filter)；来加入事件过滤回调函数.
其中.filter是一个函数指针，它有如下类型
SDL_SetEventFilter(PAL_EventFilter);
二.SDL按键处理
---------------------------------------------------------------------
按键类型是 pe == SDL_KEYDOWN,
typedef struct{
Uint8 scancode;
SDLKey sym;
SDLMod mod;
Uint16 unicode;
} SDL_keysym;
表示用户按下键盘
1.普通按键盘处理。
保存在event.key.keysym.sym 是相应的键值
keysym有如下定义
/*
SDLK_LEFTBRACKET = 91,
SDLK_BACKSLASH = 92,
SDLK_RIGHTBRACKET = 93,
SDLK_CARET = 94,
SDLK_UNDERSCORE = 95,
unicode keyboard downloadSDLK_BACKQUOTE = 96,
SDLK_a = 97,
SDLK_b = 98,
SDLK_c = 99,
SDLK_d = 100,
SDLK_e = 101,
SDLK_f = 102,
*/
int quit =false;
while( quit ==false)
{
Now we start the main loop.This loop will keep going until the user sets quit to true.//While there's an event to handle
while( SDL_PollEvent(&event ))
{
pe)
{
case SDL_QUIT:
quit =true;
break;
case SDL_KEYDOWN:
switch( event.key.keysym.sym )
{
case SDLK_UP:;break;
case SDLK_DOWN:;break;
case SDLK_a:;break;
case SDLK_RIGHT:;break;
}
break;
default:
break;
}
}
2.判断是按下组合键
d 保存组合键状态，如果检测是否按下 ALT if(lpEvent->d & KMOD_ALT)
各个组合状态如下
SDLMod Meaning
KMOD_NONE No modifiers applicable
KMOD_LSHI
FT
Left Shift is down KMOD_RSHI
FT
Right Shift is down KMOD_LCTR
L
Left Control is down KMOD_RCTR
L
Right Control is down KMOD_LALT Left Alt is down KMOD_RALT Right Alt is down KMOD_LMET
A
Left Meta is down KMOD_RMET
A
Right Meta is down KMOD_NUM Numlock is down
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