By Mark Ward
Technology correspondent, BBC News website, San Diego
Games like Crysis are hoping to push the boundaries of realism
More than good looks are needed to make a great video game, according to Glenn Entis, chief technical officer at games giant Electronic Arts.
Mr Entis told the Siggraph conference that games makers had to use much more than graphics to make their creations believable, engaging and fun.
Game worlds must not just look lifelike, he said, they must also react in a realistic manner too.
Tools that let players create content were also becoming important, he said.
Siggraph, held in San Diego, is the world's leading computer graphics conference.
During his speech, Mr Entis warned against assuming that games which look lifelike automatically take on the characteristics of the real world.
He said this problem was most acute when creating believable human video game characters.
Humans were so exquisitely sensitive to how other people move and behave, said Mr Entis, that the smallest differences undermine the almost perfect physical representations of people becoming possible on next-generation consoles such as the Xbox 360 and the PlayStation 3.
"When a character's visual appearance creates the expectation of life and it falls short your brain is going to reject that," he said.
Improvements in graphics would not boost believability, he said. "Just adding polygons makes it worse."
He said that to add authenticity EA had made extensive use of motion capture to catalogue how stance, gait and the tiny movements of facial muscles combine when people display different emotions.
Using this, he said, the game maker had created a movement system for characters that unites these gross and fine-grained changes.
"It gives us alertness and empathy that we have never really had in our games before," he said.
"Model and motion are what gives fidelity for non-interactive characters," said Mr Entis, "but it is responsiveness and intelligence that really brings them alive."
"Players have to relate to the characters they are holding in the palm of their hand," he said.
The emotion and movement matching system was going to get its first airing in the next release of EA's basketball game, NBA Live.
Similar demands held true for game worlds as well as the characters that inhabit them, said Mr Entis.
Game worlds must also react in a lifelike manner to whatever people do, he said. Often this can be done via good physics that dictates how scenery reacts when blown up or how liquids or gases move to produce an engaging, thrilling game.
"Every part of nature that can respond will respond," he said.
Mr Entis said the forthcoming Crysis title was a good example of a game in which the responsiveness of the world made it more fun to play.
"It's about worlds that look beautiful but behave beautifully as well," said Mr Entis.
Finally, he said, easy to use tools for players were growing in importance and in some cases had become as important as the gameplay itself.
For example, he said, EA research had revealed that more than half the people that played The Sims spent more than half the time they play it just making stuff - be it characters or game extras such as furniture.
"They love making the stuff so much that it becomes the game," he said.
EA was now working on a European Xbox 360 title called Virtual Me that gives players unprecedented control over the looks and wardrobe of the character they create. The game will be released alongside a TV programme put together by Big Brother creator Endemol.
The move by the games industry to give players more tools, such as the much-anticipated Spore game by Sim City creator Will Wright, was like the trend towards user-generated content seen on the web, said Mr Entis.
"It's an exploding area," he said.