8.SDL遊戲開發：事件（二）

沒上班日子無聊，沒得上班又沒錢的日子即是痛苦，在上海又換了個地，生活不容易，新地方還不錯，上網用無線，下午準備接着寫SDL系列，沒想到的是B450上fedora12 無線網卡驅動沒整上，而後我在XP和fedora12之間不停的開關機，最終驅動裝上去（lsmod 看到了），可是無線網卡仍是配置上，（iwconfig）居然找不到設備（是否是真沒裝上）。看來得去好看看網卡驅動模塊，而後回到XP上，在虛擬機上裝了個fedora17,後來發現環境什麼的都沒搞好，gcc都沒有^=^！但仍然擋不住我這顆火熱的心。接着昨天的繼續，在事件驅動中鼠標有兩個事件，分別是SDL_MouseMotionEvent 和SDL_MouseButtonEvent,前者指是在整個顯示屏上所佔的位置（x,y）關於X，Y是如何定義的，能夠這麼理解，在顯示器的左上方是原點，水平方向是X軸，垂直方向是Y軸。後者表示鼠標的點擊（單擊雙擊左擊右擊）事件，還有滾動事件，下面是關於兩個事件的結構體。關於二者具體的解釋請看結構體註釋。

typedef struct{
  Uint8 type;     /* SDL_MOUSEMOTION */
  Uint8 state;    /* 當前鼠標的狀態 */
  Uint16 x, y;    /* 鼠標此時XY的座標*/
  Sint16 xrel, yrel; /*在X / Y方向的相對運動 */
} SDL_MouseMotionEvent;

typedef struct{
  Uint8 type; /* SDL_MOUSEBUTTONDOWN OR SDL_MOUSEBUTTONUP */
  Uint8 button; /* 當前鼠標的索引它們分別是SDL_BUTTON_LEFT SDL_BUTTON_MIDDLE, SDL_BUTTON_RIGHT */
  Uint8 state;   /* SDL_PRESSED OR SDL_RELEASED */
  Uint16 x, y;   /*記錄鼠標按下或釋放時X，Y時間，（翻譯過來是這樣，可是我也不肯定）*/
} SDL_MouseButtonEvent;

大概就是這樣，鼠標的事件就如此。從鍵盤到鼠標我都關注有幾點值得注意的地方，其一是Uint8 type;其二都有Uint state；前者對應的宏還不同，從字面意思就可知道是一種型號，因此固然不一樣啦，但不一樣之間有共性那就是有DOWN和UP，當面SDL_MOUSEMOTION有點特殊。其實也就是狀態，一回事嘍！因此也就有了接下來的這個例子，Key STATE;

#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "SDL/SDL_ttf.h"
#include <string>

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *up = NULL;
SDL_Surface *down = NULL;
SDL_Surface *left = NULL;
SDL_Surface *right = NULL;
SDL_Surface *screen = NULL;

//The event structure
SDL_Event event;

//The font
TTF_Font *font = NULL;

//The color of the font
SDL_Color textColor = { 0, 0, 0 };

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;


    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;

    //Load the image
    loadedImage = IMG_Load( filename.c_str() );

    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );

        //Free the old surface
        SDL_FreeSurface( loadedImage );

        //If the surface was optimized
        if( optimizedImage != NULL )
        {
            //Color key surface
            SDL_SetColorKey( optimizedImage, SDL_SRCCOLORKEY, SDL_MapRGB( optimizedImage->format, 0, 0xFF, 0xFF ) );
        }
    }

    //Return the optimized surface
    return optimizedImage;
}

void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    SDL_Rect offset;

    offset.x = x;
    offset.y = y;

    SDL_BlitSurface( source, clip, destination, &offset );
}

bool init()
{
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 ) {
        return false;
    }

    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );

    //If there was an error in setting up the screen
    if( screen == NULL ) {
        return false;
    }

    //Initialize SDL_ttf
    if( TTF_Init() == -1 ) {
        return false;
    }

    //Set the window caption
    SDL_WM_SetCaption( "Press an Arrow Key", NULL );

    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "background.png" );

    //Open the font
    font = TTF_OpenFont( "lazy.ttf", 72 );

    //If there was a problem in loading the background
    if( background == NULL ) {
        return false;
    }

    //If there was an error in loading the font
    if( font == NULL ) {
        return false;
    }

    //If everything loaded fine
    return true;
}

void clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( up );
    SDL_FreeSurface( down );
    SDL_FreeSurface( left );
    SDL_FreeSurface( right );

    //Close the font
    TTF_CloseFont( font );

    //Quit SDL_ttf
    TTF_Quit();

    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    //Quit flag
    bool quit = false;

   //Initialize
    if( init() == false ) {
        return 1;
    }

    //Load the files
    if( load_files() == false ) {
        return 1;
    }

    //Render the text
    up = TTF_RenderText_Solid( font, "Up", textColor );
    down = TTF_RenderText_Solid( font, "Down", textColor );
    left = TTF_RenderText_Solid( font, "Left", textColor );
    right = TTF_RenderText_Solid( font, "Right", textColor );

    //While the user hasn't quit
    while( quit == false ) {
        while( SDL_PollEvent( &event ) ) {
            if( event.type == SDL_QUIT ) {
                quit = true;
            }
        }
        apply_surface( 0, 0, background, screen );

        //獲得全部鍵的狀態
        Uint8 *keystates = SDL_GetKeyState( NULL );

        //If up is pressed
        if( keystates[ SDLK_UP ] )
        {
            apply_surface( ( SCREEN_WIDTH - up->w ) / 2, ( SCREEN_HEIGHT / 2 - up->h ) / 2, up, screen );
        }

        //進行判斷
        if( keystates[ SDLK_DOWN ] )
        {
            apply_surface( ( SCREEN_WIDTH - down->w ) / 2, ( SCREEN_HEIGHT / 2 - down->h ) / 2 + ( SCREEN_HEIGHT / 2 ), down, screen );
        }

        //If left is pressed
        if( keystates[ SDLK_LEFT ] )
        {
            apply_surface( ( SCREEN_WIDTH / 2 - left->w ) / 2, ( SCREEN_HEIGHT - left->h ) / 2, left, screen );
        }

        //If right is pressed
        if( keystates[ SDLK_RIGHT ] )
        {
            apply_surface( ( SCREEN_WIDTH / 2 - right->w ) / 2 + ( SCREEN_WIDTH / 2 ), ( SCREEN_HEIGHT - right->h ) / 2, right, screen );
        }

        //Update the screen
        if( SDL_Flip( screen ) == -1 ) {
            return 1;
        }
    }   //End while quit

    //Clean up
    clean_up();

    return 0;
}

代碼真沒什麼意思，裏面有一個SDL_GetKeyState()函數，獲得了整個鍵盤的當前信息狀態。也就stata值返回給一個數組。整個數組裏面的值是一組鍵盤定義的宏，是通用的。其次還可使用SDL_GetMouseState()獲得鼠標的當前狀態信息。
到這個時候，事件也差不了吧!錯了還差的遠，還有事件同步，異步都沒提到，以及系統事件，遊戲手柄事件，窗口大小，窗口重繪，還有用戶自定義事件，平臺相關的系統事件，其中有一個退出事件，這個應該很清楚了吧，此外有組合鍵事件……

昨晚寫到這裏，原本準備發表的，可是發表不成功，因此今天上午倒騰到如今總算搞把fedora 無線上網搞點,只不過是換到fedroa17,用上去感受還不錯，至少字體，界面好看多了。有一點小小欣喜。U盤安裝fedora DVD版本（到時候我也把整個安裝過程遇到的問題和你們一塊兒分享下。