I. Artist Statement / Why Factor

Liquefaction is a fast-paced game centered around fluid dynamics based gameplay. The visualization of fluid flow is often very stimulating, both aesthetically and intellectually. A game that takes advantage this, will have the opportunity to be very compelling to play. Such a game can even educate the player in addition to entertain.

II. Previous Games / Influences

My development of this game has been strongly influenced by two existing games. The overall feel and play of my game has been modeled after the game Rez. Specifically, I attempted to achieve the same integration of visuals with music and sound. The fluidity of gameplay used in Rez has also influenced the development of Liquefaction. The second main influence on Liquefaction is the children’s game Rocky’s Boots. This game has provided me with a model of a game that can still be fun to play while having the main purpose of education. Although Liquefaction is not an overt teaching tool, the users must first learn some basics of fluid dynamic behavior in order to take full advantage of the gaming experience.

Fluent is a computational fluid dynamics program designed to accurately predict fluid flow and is used as a scientific tool. Despite this, my work with Fluent has influenced my views on the visualization of fluid dynamic behavior. The escalating difficulty between levels through the increase in game pace is an idea that comes from my experience with Tetris.

III. Target Audience

A game like Liquefaction will probably appeal to a large audience. Ideally, the controls for this game remain very simple. The only lower limit on age that I can foresee is the development of the motor skills and reaction time necessary to achieve the goals of the game. Since Liquefaction does not contain any plot, people who do not have a large amount of time to devote to gaming will also have the opportunity to play.

IV. Introduction and Story

Liquefaction has no story whatsoever. The only introduction that is needed is a short instructional tutorial which is provided as a web page.

V. Long Term Project Impact

The only foreseeable project impact is an increased interest in fluid dynamics. Because the game remains true to the governing fluid dynamic equations, someone who enjoys playing Liquefaction may become curious of the theory behind the game.

VI. Delivery System and Requirements

Due to my own development restrictions, this game can be played on personal computers running Microsoft Windows only. It also makes use of the standard PC equipment such as the monitor, mouse, speakers and keyboard. The gameplay mostly requires mouse input, but may have minimal keyboard interaction in future versions. Both the monitor and speakers are very involved in the game output.

VII. Interface

Liquefaction is played in a top-down view of a two dimensional flow field. Scoring information is located in a bar positioned across the bottom of the screen. A bar at the top of the screen is intended to hold inventory information. The flow field is visualized by a background of particles whose movement is induced by the flow field itself. Fluid dynamic controls are represented by animated icons indicating the type of influence they have over the flow field. The interface also displays the objects that are “floating” in the flow.

VIII. User Interaction

The player can place two types of flow controls. These controls are placed directly of the flow field using the left or right mouse buttons. Items in the player’s possession are placed using the keyboard. Using these tools, the player is able to maintain control over the flow field.

IX. World Layout / Level Design

The world of Liquefaction moves from right to left. Present in this world are source controls which emit fluid. These sources disturb the flow field and can limit the amount of control the player has over the flow. The world also contains colored clouds and items which can be absorbed by the player. The levels are all randomly generated on the fly. The types of clouds and items present in the world are dictated by the current level of play. The placement of these clouds and items relative to each other is such that a skillful player would be able to separate them if this is needed.

XII. Music / Sound Design

The music and sound are both very important to Liquefaction. The music and sound in Liquefaction are designed to help immerse the player in the game. Many of the game’s events are timed to coincide with the musical beat. Each successive level has unique music which consists of an increasingly complex variation of the previous level. In this way, the music of the first level is very simple, and the music of more advanced levels relatively complex. Every event in Liquefaction has an associated sound. These sounds serve to provide the player with auditory notifications in addition to visual signs.

All of the music was written for Liquefaction by Willy Joy. The sounds are based on sounds also created by Willy Joy.

XIII. Rules and Gameplay

The gameplay is structured around a stationary sink in the flow field. The sink corresponds to the player and absorbs surrounding fluid. When a colored cloud is absorbed by the sink, it can either increase or decrease the progress bar. Green clouds increase the progress bar while red decreases it. When the progress bar fills up, an energy token is provided to the player. The level is completed after all eight energy tokens have been enabled.

The player is able to control what flows into the sink by manipulating the flow field. This is done by placing either clockwise or counterclockwise vortices. Vortices are only created on the beat. When a vortex is placed, an energy token is drained (but remains available). Energy tokens regenerate slowly and should be used sparingly. A vortex can be added to an existing vortex or source without using any energy. A vortex placed this way is also created instantly. When more than one vortex is added to the same control, the strength of the vortex increases or decreases accordingly.

XIV. Program Structure

The program is structured around the implementation of the flow field. The inviscid flow calculations are all performed by a single standard fourth order Runge-Kutta numeric solver. All object classes that can be moved by the RK4 solver inherit from a single movable class. Likewise, all object classes that control the flow share inheritance. The level transition animation is generated in real time by a custom particle 3D engine. Many of the mathematical computations performed in the program including those of both the flow field and transition animation employ a two or three dimensional vector class.

XV. Technical Specs

The fluid dynamic model is set up to simulate inviscid, incompressible, irrotational Newtonian flow. This type of behavior is governed by modified Navier-Stokes equations and has a linear solution. As stated above, the equations of fluid motion are solved using a standard fourth order Runge-Kutta numeric solver. All flow controls are modeled as singular filaments.

The graphics are drawn using the Simple DirectMedia Layer (SDL) library and the Open Graphics Library (OpenGL). Prerendered graphics are created when the program starts up and then displayed using OpenGL. The sound and music are played using the SDL Mixer Library. Music files are compressed in the Ogg Vorbis format, and sounds are Windows RIFF WAVE files.

XVI. Implementation

The program was written entirely in C++ linking to the SDL, SDL_Mixer and OpenGL libraries. It was compiled using Microsoft Visual C++ 6.0.

XIX. References

Heath, Michael T. Scientific Computing. New York: McGraw-Hill, 2002.

Kuethe, Arnold and Chuen-Yen Chow. Foundations of Aerodynamics. New York: John Wiley & Sons, 1998.

Shreiner, Dave, ed. OpenGL Reference Manual. Indianapolis: Addison Wesley, 2000.