typedef struct SDL_Surface {
Uint32 flags; /* Read-only */
SDL_PixelFormat *format; /* Read-only */
int w, h; /* Read-only */
Uint16 pitch; /* Read-only */
void *pixels; /* Read-write */
/* clipping information */
SDL_Rect clip_rect; /* Read-only */
/* Reference count -- used when freeing surface */
int refcount; /* Read-mostly */
/* This structure also contains private fields not shown here */
} SDL_Surface;
SDL_Surface's represent areas of "graphical" memory, memory that can be drawn to. The video framebuffer is returned as a SDL_Surface by SDL_SetVideoMode and SDL_GetVideoSurface. Most of the fields should be pretty obvious. w and h are the width and height of the surface in pixels. pixels is a pointer to the actual pixel data, the surface should be locked before accessing this field. The clip_rect field is the clipping rectangle as set by SDL_SetClipRect.
The following are supported in the flags field.
SDL_PixelFormat