SDL几个重要的函数理解

/** Restart one of the threads that are waiting on the condition variable,
 *  @return 0 or -1 on error.
 */
extern DECLSPEC int SDLCALL SDL_CondSignal(SDL_cond *cond);


/** Wait on the condition variable, unlocking the provided mutex.
 *  The mutex must be locked before entering this function!
 *  The mutex is re-locked once the condition variable is signaled.
 *  @return 0 when it is signaled, or -1 on error.
 */
extern DECLSPEC int SDLCALL SDL_CondWait(SDL_cond *cond, SDL_mutex *mut);
/*
width 与 height 的比例会直接影响视频的显示比例。
如：width *= 2 ;则宽度变为原来的 1/2  。同样height *＝ 2 ，则高度变为原来的 1/2
似乎没有改变视频后面的屏幕。
*/
extern DECLSPEC SDL_Overlay * SDLCALL SDL_CreateYUVOverlay(int width, int height,
				Uint32 format, SDL_Surface *display);

/***
srcW、srcH:源视频的宽度、高度
dstW、dstH:目标视频的宽度、高度
**/
struct SwsContext *sws_getContext(int srcW, int srcH, int srcFormat, int dstW, 
		int dstH, int dstFormat, int flags, SwsFilter *srcFilter, 
		SwsFilter *dstFilter, double *param);

/**
 * Set up a video mode with the specified width, height and bits-per-pixel.
 *
 * If 'bpp' is 0, it is treated as the current display bits per pixel.
 *
 * If SDL_ANYFORMAT is set in 'flags', the SDL library will try to set the
 * requested bits-per-pixel, but will return whatever video pixel format is
 * available.  The default is to emulate the requested pixel format if it
 * is not natively available.
 *
 * If SDL_HWSURFACE is set in 'flags', the video surface will be placed in
 * video memory, if possible, and you may have to call SDL_LockSurface()
 * in order to access the raw framebuffer.  Otherwise, the video surface
 * will be created in system memory.
 *
 * If SDL_ASYNCBLIT is set in 'flags', SDL will try to perform rectangle
 * updates asynchronously, but you must always lock before accessing pixels.
 * SDL will wait for updates to complete before returning from the lock.
 *
 * If SDL_HWPALETTE is set in 'flags', the SDL library will guarantee
 * that the colors set by SDL_SetColors() will be the colors you get.
 * Otherwise, in 8-bit mode, SDL_SetColors() may not be able to set all
 * of the colors exactly the way they are requested, and you should look
 * at the video surface structure to determine the actual palette.
 * If SDL cannot guarantee that the colors you request can be set, 
 * i.e. if the colormap is shared, then the video surface may be created
 * under emulation in system memory, overriding the SDL_HWSURFACE flag.
 *
 * If SDL_FULLSCREEN is set in 'flags', the SDL library will try to set
 * a fullscreen video mode.  The default is to create a windowed mode
 * if the current graphics system has a window manager.
 * If the SDL library is able to set a fullscreen video mode, this flag 
 * will be set in the surface that is returned.
 *
 * If SDL_DOUBLEBUF is set in 'flags', the SDL library will try to set up
 * two surfaces in video memory and swap between them when you call 
 * SDL_Flip().  This is usually slower than the normal single-buffering
 * scheme, but prevents "tearing" artifacts caused by modifying video 
 * memory while the monitor is refreshing.  It should only be used by 
 * applications that redraw the entire screen on every update.
 *
 * If SDL_RESIZABLE is set in 'flags', the SDL library will allow the
 * window manager, if any, to resize the window at runtime.  When this
 * occurs, SDL will send a SDL_VIDEORESIZE event to you application,
 * and you must respond to the event by re-calling SDL_SetVideoMode()
 * with the requested size (or another size that suits the application).
 *
 * If SDL_NOFRAME is set in 'flags', the SDL library will create a window
 * without any title bar or frame decoration.  Fullscreen video modes have
 * this flag set automatically.
 *
 * This function returns the video framebuffer surface, or NULL if it fails.
 *
 * If you rely on functionality provided by certain video flags, check the
 * flags of the returned surface to make sure that functionality is available.
 * SDL will fall back to reduced functionality if the exact flags you wanted
 * are not available.
 */
/*改变该函数的 int width, int height, 两个参数，表现出来的，就是播放视频程序框框的大小尺寸*/
extern DECLSPEC SDL_Surface * SDLCALL SDL_SetVideoMode
			(int width, int height, int bpp, Uint32 flags);