Harri Hakonen

A survey of longest common subsequence algorithms

The aim of this paper is to give a comprehensive comparison of well-known longest common subsequence algorithms (for two input strings) and study their behaviour in various application environments. The performance of the methods depends heavily on the properties of the problem instance as well as the supporting data structures used in the implementation. We want to make also a clear distinction between methods that determine the actual lcs and those calculating only its length, since the execution time and more importantly, the space demand depends crucially on the type of the task. To our knowledge, this is the first time this kind of survey has been done. Due to the page limits, the paper gives only a coarse overview of the performance of the algorithms; more detailed studies are reported elsewhere.

Aspects of networking in multiplayer computer games

Distributed, real‐time multiplayer computer games (MCGs) are in the vanguard of utilizing the networking possibilities. Although related research has been done in military simulations, virtual reality systems, and computer supported cooperative working, the suggested solutions diverge from the problems posed by MCGs. With this in mind, this paper provides a concise overview of four aspects affecting networking in MCGs. First, networking resources (bandwidth, latency, and computational power) set the technical boundaries within which the MCG must operate. Second, distribution concepts encompass communication architectures (peer‐to‐peer, client/server, server‐network), and both data and control architectures (centralized, distributed, replicated). Third, scalability allows the MCG to adapt to the resource changes by parametrization. Finally, security aims at fighting back against cheating and vandalism, which are common in online gaming.

Realizing the bullet time effect in multiplayer games with local perception filters

Local perception filters exploit the limitations of human perception to reduce the effects of network latency in multiplayer computer games. Because they allow temporal distortions in the rendered view, they can be modified to realize the bullet time effect, where a player can get more reaction time by slowing down the surrounding game world. In this paper, we examine the concepts behind local perception filters and extend them to cover artificially increased delays. The presented methods are implemented in a testbench program, which is used to study the usability and limitations of the approach.

New Refinement Techniques for Longest Common Subsequence Algorithms

Certain properties of the input strings have dominating influence on the running time of an algorithm selected to solve the longest common subsequence (lcs) problem of two input strings. It has turned out to be difficult – as well theoretically as practically – to develop an lcs algorithm which would be superior for all problem instances. Furthermore, implementing the most evolved lcs algorithms presented recently is laborious.

Realizing bullet time effect in multiplayer games with local perception filters

Local perception filters exploit the limitations of human perception to reduce the effects of network latency in multiplayer computer games. Because they allow temporal distortions in the rendered view, they can be modified to realize bullet time effect, where a player can get more reaction time by slowing down the surrounding game world. In this paper, we examine the concepts behind local perception filters and extend them to cover artificially increased delays. The presented methods are implemented in a testbench program, which is used to study the usability and limitations of the approach.

Developer Driven Approach to Situational Method Engineering

This position paper reflects SME into software development. We argue that to apply SME in software development projects, construction of method fragments should also take place during the project by the method users. The topic is current due to two key technologies, EPF and SPEM, that enable illustrative and prompt method construction. The paper looks at the relevant background in both SME and software development processes, identifies four levels of method management work, discusses the method reuse strategy, and presents an example of on-the-fly method construction.

Preventing look-ahead cheating with active objects

In a turn-based networked multiplayer computer game, it is possible to cheat by delaying the announcement of ones action for a turn until one has received messages from all the other players. This look-ahead cheating can be prevented with a lockstep protocol, which requires that the player first announces a commitment to an action and later on the action itself, which can be compared with the earlier announced commitment. However, because the lockstep protocol requires separate transmissions for the commitment and the action and a synchronization step before the actions can be announced, it slows down the turns of the game. In this paper, we propose that active objects can be used to prevent look-ahead cheating. Moreover, we can parameterize the probability of catching cheaters: The smaller this probability is, the less bandwidth and transmissions are required. In most cases, the mere threat of getting caught is enough to discourage cheating, and, consequently, this probability can be quite small.