"A simulation is cool, but it must be enjoyable to the player," says Eric Chahi, director of Ubisoft's wildly ambitious downloadable title, tentatively called Project Dust, which currently runs on the Xbox 360, PlayStation 3, and PC. In the game, players can re-terraform the world around them, creating islands, rivers, and life using simple tools that interact with each other intelligently. The Another World creator's talk at GDC Europe centered on the idea that with a correct meeting of technology and game design, you can create something truly unique. To do that, he says you must "keep only the essentials for the purposes of optimization, and to keep these things simple for the player." Since the high-level idea of the game is rather conceptual -- you are keeping a tribe of humans alive in this changing environment -- the interface has to be simple. But in a game where mud is actually created dynamically by water flowing, the technology behind such a simple interface is intense. "We have to think in terms of convergence," says Chahi, adding that they had to create new rules to conceive this meeting of technology and gameplay. "We do not create a river -- the river is created from a conversion of the rules. A river is created by water flowing, and soil moving." This concept is adaptive to different situations - the river is just one example. "The earth is a living thing within the game," he says. The terrain changes by itself at times, the player acts on it, and gameplay becomes really creative in this kind of environment, Chahi asserts. Lakes, volcanoes, and the like all require rules for correct convergence. "We have to avoid geometrical patterns," he noted, showing a slide of a previous iteration in which there were square-looking lava flows -- "It's partly because the game is made on [an underlying] grid, so we have to fight against that." The trouble with rules is that weird patterns can emerge, so the convergence of this technology has to be carefully managed with design, he says: "The difficulty is how to tune this." The game designers constantly ask for changes to features, and every time this happened, "we had to tune all the parameters. Sometimes it would take days to find the right value for gameplay that's also aesthetically pleasing." Still, "often the implementation is an inspiration," he says, noting their solution for creation of mud. They already had sediment in water in their simulation, but no viscosity. Wet mud now contains 100 percent sediment with high viscosity, so it spreads like honey. The simulation can make this work for them, creating soil. "The relationship between the technology and the game design was fundamental to the simulation," he added. "To create a landscape, we're using the dynamic properties of these simulated layers." In the future, the game may also have real-time weather simulation. "It will be done eventually. I don't know if it's in the first release or not," he said. Ronan Bel, the game's technical director, noted that all the tools in the game are made by the team itself. "It's more fun to make it by ourselves," he said, though moments before he had just made a shooting pantomime in Chahi's direction at the discussion of adding real-time weather. What led Chahi to make a simulation that so curiously mimics real-world environmental changes? "Regarding the universe, well - it was a personal experience, based on the personal experience of being on a volcano," he said, seeing it as a living world. In the game, for the player "the land becomes his property. It's almost a character in the game. Even if it's not the main gameplay, it's really interesting."