这是简单Directmedia层，提供低 级别来访问音频，键盘，鼠标，操纵杆，通过OpenGL三维硬件， 跨多个平台和2D帧缓冲。-This is the Simple DirectMedia Layer, a general API that provides low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D framebuffer across mult