Andrew Huang
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。
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/** 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;
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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
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/** 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;
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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）
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typedef struct SDL_QuitEvent {
Uint8 type; /**< SDL_QUIT */
} SDL_QuitEvent;
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按键处理事件
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/** 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;
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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
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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;
}
}
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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,
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typedef struct{
Uint8 scancode;
SDLKey sym;
SDLMod mod;
Uint16 unicode;
} SDL_keysym;
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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
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/*
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;
}
}
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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
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SDLMod |
Meaning |
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KMOD_NONE |
No modifiers applicable |
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KMOD_LSHIFT |
Left Shift is down |
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KMOD_RSHIFT |
Right Shift is down |
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KMOD_LCTRL |
Left Control is down |
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KMOD_RCTRL |
Right Control is down |
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KMOD_LALT |
Left Alt is down |
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KMOD_RALT |
Right Alt is down |
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KMOD_LMETA |
Left Meta is down |
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KMOD_RMETA |
Right Meta is down |
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KMOD_NUM |
Numlock is down |
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KMOD_CAPS |
Capslock is down |
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KMOD_MODE |
Mode is down |
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KMOD_CTRL |
A Control key is down |
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KMOD_SHIFT |
A Shift key is down |
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KMOD_ALT |
An Alt key is down |
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KMOD_META |
A Meta key is down |
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