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SDL Guide 中文译版(三下)

2008-04-09 04:27:34来源：互联网阅读 ()

第三章下键盘输入

键盘相关数据结构

SDLKey 枚举类型，每一个符号代表一个键，如SDLK_a、SDLK_SPACE，在SDL_keysym.h中定义。
SDLMod 枚举类型，类似SDLKey，但用于修饰键，如Control、Alt、Shift，可以组合。
SDL_keysym
```
typedef struct{
  Uint8 scancode;
  SDLKey sym;
  SDLMod mod;
  Uint16 unicode;
} SDL_keysym;
```
用于按键和放开消息。scancode是硬件相关键码。除非你有特殊用途，否则忽略。sym指示键，mod为修饰键集合，例如KMOD_NUM | KMOD_CAPS | KMOD_LSHIFT 为Numlock、Capslock和左Shift组合。最后unicode为对应字符。注意，仅当是按键消息时unicode才有效，放开消息时无效。Unicode变换必须用SDL_EnableUNICODE()打开。
SDL_KeyboardEvent
```
typedef struct{
  Uint8 type;
  Uint8 state;
  SDL_keysym keysym;
} SDL_KeyboardEvent;
```
描述一个键盘消息。type指示按键（SDL_KEYDOWN）或放开（SDL_KEYUP）。state是冗余的，和含义type相同只是符号不同（SDL_PRESSED，SDL_RELEASED）。

读取键盘消息

使用消息循环用SDL_PollEvent()从消息队列里读取，并用switch-case检测SDL_KEYUP和SDL_KEYDOWN。下面是个基本的例子。

例3-10 读键盘消息

  SDL_Event event;
  .
  .
  /* Poll for events. SDL_PollEvent() returns 0 when there are no  */
  /* more events on the event queue, our while loop will exit when */
  /* that occurs.                                                  */
  while( SDL_PollEvent( &event ) ){
    /* We are only worried about SDL_KEYDOWN and SDL_KEYUP events */
    switch( event.type ){
      case SDL_KEYDOWN:
        printf( "Key press detected\n" );
        break;

      case SDL_KEYUP:
        printf( "Key release detected\n" );
        break;

      default:
        break;
    }
  }

更详细的内容

我们已经知道要用SDL_Init和SDL_SetVideoMode初始化，但我们还得用另外两个函数取得必要信息。要调用SDL_EnableUNICODE(1)以允许unicode变换，还要用SDL_GetKeyName将SDLKey转换成可打印字符。注意：小于0x80的unicode字符直接映射到ASCII码。下例用到这一点。

例3-11 解释按键消息

    #include "SDL.h"

    /* Function Prototypes */
    void PrintKeyInfo( SDL_KeyboardEvent *key );
    void PrintModifiers( SDLMod mod );

    /* main */
    int main( int argc, char *argv[] ){
        
        SDL_Event event;
        int quit = 0;
        
        /* Initialise SDL */
        if( SDL_Init( SDL_INIT_VIDEO ) ){
            fprintf( stderr, "Could not initialise SDL: %s\n", SDL_GetError() );
            exit( -1 );
        }

        /* Set a video mode */
        if( !SDL_SetVideoMode( 320, 200, 0, 0 ) ){
            fprintf( stderr, "Could not set video mode: %s\n", SDL_GetError() );
            SDL_Quit();
            exit( -1 );
        }

        /* Enable Unicode translation */
        SDL_EnableUNICODE( 1 );

        /* Loop until an SDL_QUIT event is found */
        while( !quit ){

            /* Poll for events */
            while( SDL_PollEvent( &event ) ){
                
                switch( event.type ){
                    /* Keyboard event */
                    /* Pass the event data onto PrintKeyInfo() */
                    case SDL_KEYDOWN:
                    case SDL_KEYUP:
                        PrintKeyInfo( &event.key );
                        break;

                    /* SDL_QUIT event (window close) */
                    case SDL_QUIT:
                        quit = 1;
                        break;

                    default:
                        break;
                }

            }

        }

        /* Clean up */
        SDL_Quit();
        exit( 0 );
    }

    /* Print all information about a key event */
    void PrintKeyInfo( SDL_KeyboardEvent *key ){
        /* Is it a release or a press? */
        if( key->type == SDL_KEYUP )
            printf( "Release:- " );
        else
            printf( "Press:- " );

        /* Print the hardware scancode first */
        printf( "Scancode: 0xX", key->keysym.scancode );
        /* Print the name of the key */
        printf( ", Name: %s", SDL_GetKeyName( key->keysym.sym ) );
        /* We want to print the unicode info, but we need to make */
        /* sure its a press event first (remember, release events */
        /* don''''t have unicode info                                */
        if( key->type == SDL_KEYDOWN ){
            /* If the Unicode value is less than 0x80 then the    */
            /* unicode value can be used to get a printable       */
            /* representation of the key, using (char)unicode.    */
            printf(", Unicode: " );
            if( key->keysym.unicode < 0x80 && key->keysym.unicode > 0 ){
                printf( "%c (0xX)", (char)key->keysym.unicode,
                        key->keysym.unicode );
            }
            else{
                printf( "? (0xX)", key->keysym.unicode );
            }
        }
        printf( "\n" );
        /* Print modifier info */
        PrintModifiers( key->keysym.mod );
    }

    /* Print modifier info */
    void PrintModifiers( SDLMod mod ){
        printf( "Modifers: " );

        /* If there are none then say so and return */
        if( mod == KMOD_NONE ){
            printf( "None\n" );
            return;
        }

        /* Check for the presence of each SDLMod value */
        /* This looks messy, but there really isn''''t    */
        /* a clearer way.                              */
        if( mod & KMOD_NUM ) printf( "NUMLOCK " );
        if( mod & KMOD_CAPS ) printf( "CAPSLOCK " );
        if( mod & KMOD_LCTRL ) printf( "LCTRL " );
        if( mod & KMOD_RCTRL ) printf( "RCTRL " );
        if( mod & KMOD_RSHIFT ) printf( "RSHIFT " );
        if( mod & KMOD_LSHIFT ) printf( "LSHIFT " );
        if( mod & KMOD_RALT ) printf( "RALT " );
        if( mod & KMOD_LALT ) printf( "LALT " );
        if( mod & KMOD_CTRL ) printf( "CTRL " );
        if( mod & KMOD_SHIFT ) printf( "SHIFT " );
        if( mod & KMOD_ALT ) printf( "ALT " );
        printf( "\n" );
    }

			   
			   
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