事件驱动与状态驱动事件驱动与状态驱动

假设有这么一个场景，是用键盘的方向键去控制一个物体前进的方向，其中有down、up、right和left，大家很容易想到的是事件驱动，大概模型如下：

/* Alien screen coordinates */ int alien_x=0, alien_y=0; /* Main game loop */ /* Check for events */ while( SDL_PollEvent( &event ) ){ switch( event.type ){ /* Look for a keypress */ case SDL_KEYDOWN: /* Check the SDLKey values and move change the coords */ switch( event.key.keysym.sym ){ case SDLK_LEFT: alien_x -= 1; break; case SDLK_RIGHT: alien_x += 1; break; case SDLK_UP: alien_y -= 1; break; case SDLK_DOWN: alien_y += 1; break; default: break; } } } }

但是，键盘事件只有在一个按键发生状态改变时才会发生，所以，上述的模型中，要移动100个距离，就要按100次键盘。为了避免这个问题，几乎所有游戏都是采用状态驱动的模型，如下：

/* Alien screen coordinates */ int alien_x=0, alien_y=0; int alien_xvel=0, alien_yvel=0; /* Main game loop */ /* Check for events */ while( SDL_PollEvent( &event ) ){ switch( event.type ){ /* Look for a keypress */ case SDL_KEYDOWN: /* Check the SDLKey values and move change the coords */ switch( event.key.keysym.sym ){ case SDLK_LEFT: alien_xvel = -1; break; case SDLK_RIGHT: alien_xvel =1; break; case SDLK_UP: alien_yvel = -1; break; case SDLK_DOWN: alien_yvel =1; break; default: break; } break; /* We must also use the SDL_KEYUP events to zero the x */ /* and y velocity variables. But we must also be*/ /* careful not to zero the velocities when we shouldn't*/ case SDL_KEYUP: switch( event.key.keysym.sym ){ case SDLK_LEFT: /* We check to make sure the alien is moving */ /* to the left. If it is then we zero the*/ /* velocity. If the alien is moving to the*/ /* right then the right key is still press*/ /* so we don't tocuh the velocity*/ if( alien_xvel < 0 ) alien_xvel = 0; break; case SDLK_RIGHT: if( alien_xvel > 0 ) alien_xvel = 0; break; case SDLK_UP: if( alien_yvel < 0 ) alien_yvel = 0; break; case SDLK_DOWN: if( alien_yvel > 0 ) alien_yvel = 0; break; default: break; } break; default: break; } }/* Update the alien position */ alien_x += alien_xvel; alien_y += alien_yvel;

【事件驱动与状态驱动】转载于:https://www.cnblogs.com/littlethank/archive/2012/07/04/2575877.html