这次我们看看如何在SDL中处理键盘事件，每次事件发生以后，有关事件的所有信息都存储在SDL_Event类型的变量当中，查查手册我们可以知道，实际SDL_Event是一个联合体。
typedef union{
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_SywWMEvent syswm;
} SDL_Event;
当发生键盘事件时，key变量就是有效的。
typedef struct{
Uint8 type;
Uint8 state;
SDL_keysym keysym;
} SDL_KeyboardEvent;
key变量是一个结构体，其中keysym成员包含了按键信息。
typedef struct{
Uint8 scancode;
SDLKey sym;
SDLMod mod;
Uint16 unicode;
} SDL_keysym;
在keysym的成员当中，sym记录按键所对应的虚拟键。
比如说向上就是SDLK_UP；向下就是SDLK_DOWN；大家可以自己去查手册。
下面就看一个处理键盘消息的实例吧。
该例子中，我们一旦发现有上下左右四个键被按下，就马上在屏幕上显示相对应的消息，这里用到了扩展类库SDL_TTF，如有不清楚的，参考一下前面的几篇文章。
#include "SDL.h"
#include "SDL_ttf.h"
SDL_Surface *screen=NULL;
SDL_Surface *up=NULL;
SDL_Surface *down=NULL;
SDL_Surface *left=NULL;
SDL_Surface *right=NULL;
SDL_Surface *message=NULL;
TTF_Font *font=NULL;
//screen to show on window
const int SCREEN_BPP=32;
SDL_Color textColor=
{255,255,255};
int main( int argc, char* args[] )
{
//Start SDL
bool quit=false;
SDL_Init( SDL_INIT_EVERYTHING );
if(TTF_Init()==-1)
return false;
screen = SDL_SetVideoMode( 600, 480, SCREEN_BPP, SDL_SWSURFACE );
if(screen==NULL)
return false;
font=TTF_OpenFont("tahoma.ttf",28);
up = TTF_RenderText_Solid( font, "Up was pressed.", textColor );
down = TTF_RenderText_Solid( font, "Down was pressed.", textColor );
left = TTF_RenderText_Solid( font, "Left was pressed", textColor );
right = TTF_RenderText_Solid( font, "Right was pressed", textColor );
SDL_Event event;
while(!quit)
{
if(SDL_PollEvent(&event))
{
if(event.type == SDL_KEYDOWN)
{
switch(event.key.keysym.sym)
{
case SDLK_UP: message=up;break;
case SDLK_DOWN: message=down;break;
case SDLK_LEFT: message=left;break;
case SDLK_RIGHT: message=right;break;
}
}
if(event.type == SDL_QUIT)
quit=true;
}
if(message != NULL)
{
Uint32 colorVal=SDL_MapRGB(screen->format,0,0,0);
SDL_FillRect(screen, &screen->clip_rect,colorVal);
SDL_BlitSurface(message,NULL,screen,NULL);
message=NULL;
}
if(SDL_Flip(screen) == -1)
{
return false;
}
}
//Quit SDL
SDL_Quit();
return 0;
}
