Either the quality of graphics or the frame rate has to be sacrificed when games are running in 3D.
That's according to Mathieu Girard, the senior producer of multi-platform real-time strategy game R.U.S.E., who reckons that in some cases "3D games are going to look a bit less good than original games".
"For 3D on console, you must have, I would say, at least 60 frames per second, because, basically, you draw two images to achieve 3D," Girard told Eurogamer. "Your game has to deliver twice as many frames to still remain fluid in 3D.
"You must have twice as many frames, so either you're losing the 60 frames per second, or you are losing the quality of graphics. I cannot imagine a game with all the polished graphical quality running at 120 hertz so that each image is 60 hertz. Something has to be reduced somewhere. It's tricky."
One developer who may argue with Girard is Crytek founder Cevat Yerli. At E3 2010 he told VideoGamer that the impact of running upcoming shooter Crysis 2 in 3D is negligible.
"Whenever we show 3D, we show it intentionally on 360 to make the point. It works. It works flawless on PS3, 360 and PC as well. It just works; and one-and-a-half per cent impact only. Out of 30 frames it's 0.4 frames," he said.
"I use the term 'for free', with this game. It's so negligible. And people ask, how do you do it? I say, well, we do render only once. That isn't magic. But we create a second image out of the first one. But how we do it is the magic. That's the secret sauce. I'm happy that we figured it out!"
So, what's the truth? According to Digital Foundry's Richard Leadbetter, who analysed the performance of PlayStation 3D after E3, Girard's comments make sense.
"Girard is quite correct," Leadbetter said. "Rendering in proper stereoscopic 3D incurs a significant overhead over normal 2D. Basically the exact same scene is being rendered twice - once for each eye. Challenges are two-fold then: to begin with, double the amount of pixels need to be generated, and secondly the scene geometry (the basic 3D shapes that comprise the image) need to be drawn twice to accommodate the different views per eye.
"An alternative is 3D based on a 2D image plus depth, as seen in Crysis 2 on console. Here the scene is just rendered the once, but with separate offsets for each eye calculated from the game's internal depth map. The result is much faster, but can create "gaps" in the image. For example, if you're standing next to a wall that covers the view of one eye, but not the other. It'll be interesting to see how or indeed if Crytek overcomes this."
Perhaps it goes without saying that 3D is beyond R.U.S.E. at this point.
"I would say no plans," Girard confirmed. "We have some stuff on PC but it's very… secret right now. So right now with a game of the magnitude of R.U.S.E. it's a bit too complex either on Xbox 360 or Sony, to achieve that [3D].
"I think a game has to be thought for 3D at the beginning to make sure it has the performance necessary in the end. Maybe that means that 3D games are going to look a bit less good than original games."
R.U.S.E. is due out on 17th September.