libopenshot/include/Cache.h

#ifndef OPENSHOT_CACHE_H
#define OPENSHOT_CACHE_H

/**
 * \file
 * \brief Header file for Cache class
 * \author Copyright (c) 2011 Jonathan Thomas
 */

#include <map>
#include <deque>
#include "Frame.h"
#include "Exceptions.h"

/// This namespace is the default namespace for all code in the openshot library.
namespace openshot {

	/**
	 * \brief This class is a cache manager for Frame objects.  It is used by FileReaders (such as FFmpegReader) to cache
	 * recently accessed frames.
	 *
	 * Due to the high cost of decoding streams, once a frame is decoded, converted to RGB, and a Frame object is created,
	 * it critical to keep these Frames cached for performance reasons.  However, the larger the cache, the more memory
	 * is required.  You can set the max number of previous frames (relative to the current frame) to cache.  Frames that
	 * come after the current frame are allowed to increase as much as needed (a requirement of the file readers).  A call
	 * to GetFrame() sets the current frame of the cache.
	 */
	class Cache {
	private:
		int max_frames;				///< This is the max number of "previous" frames to cache
		map<int, Frame*> frames;		///< This map holds the frame number and Frame objects
		deque<int> frame_numbers;	///< This queue holds a sequential list of cached Frame numbers
		int current_frame;			///< This is the last requested frame (used to dynamically adjust the max_frames)

		/// Clean up cached frames that exceed the max number of previous frames
		void CleanUp();

	public:
		/// Default constructor, max previous frames to cache is 20
		Cache();

		/// Constructor that sets the max previous frames to cache
		Cache(int max_frames);

		/// Add a Frame to the cache
		void Add(int frame_number, Frame* frame);

		/// Check for the existence of a frame in the cache
		bool Exists(int frame_number);

		/// Get a frame from the cache
		Frame* GetFrame(int frame_number);

		/// Get the smallest frame number
		Frame* GetSmallestFrame();

		/// Remove a specific frame
		void Remove(int frame_number);

		/// Remove a specific frame
		void Remove(int frame_number, bool delete_data);

		/// Clear the cache of all frames
		void Clear();

		/// Display a list of cached frame numbers
		void Display();

		/// Display the list of cache and clear the cache (mainly for debugging reasons)
		void DisplayAndClear();

		/// Count the frames in the queue
		int Count();

		/// Set current frame number (used to determine which previous frames to delete)
		void SetCurrentFrame(int frame_number) { current_frame = frame_number; CleanUp(); };

		/// Get the current frame number (used to determine which previous frames to delete)
		int GetCurrentFrame() { return current_frame; };

		/// Set maximum frames to a different amount
		void SetMaxFrames(int number_of_frames) { max_frames = number_of_frames; };

		/// Gets the maximum frames value
		int GetMaxFrames() { return max_frames; };

	};

}

#endif