SDL_GetClipRect man page
SDL_GetClipRect — Gets the clipping rectangle for a surface.
void SDL_GetClipRect(SDL_Surface *surface, SDL_Rect *rect);
Gets the clipping rectangle for a surface. When this surface is the destination of a blit, only the area within the clip rectangle is drawn into.
The rectangle pointed to by rect will be filled with the clipping rectangle of the surface.
SDL_SetClipRect, SDL_BlitSurface, SDL_Surface