SDL事件循环及按键处理

时间：2010-08-21 来源：bluedrum

Andrew Huang [email protected] 一.事件循环 ------------------------------------------------------ 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 ) )
        {
             switch(event.type)
             {
             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 event.type == 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,
    SDLK_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 ) )
        {
             switch(event.type)
             {
             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

key.keysym.mod 保存组合键状态，如果检测是否按下 ALT

if(lpEvent->key.keysym.mod & KMOD_ALT)

各个组合状态如下

SDLMod	Meaning
KMOD_NONE	No modifiers applicable
KMOD_LSHIFT	Left Shift is down
KMOD_RSHIFT	Right Shift is down
KMOD_LCTRL	Left Control is down
KMOD_RCTRL	Right Control is down
KMOD_LALT	Left Alt is down
KMOD_RALT	Right Alt is down
KMOD_LMETA	Left Meta is down
KMOD_RMETA	Right Meta is down
KMOD_NUM	Numlock is down
KMOD_CAPS	Capslock is down
KMOD_MODE	Mode is down
KMOD_CTRL	A Control key is down
KMOD_SHIFT	A Shift key is down
KMOD_ALT	An Alt key is down
KMOD_META	A Meta key is down