For the past 20 years, virtual reality has been just that: a technological dream that failed to break through into the real world. The previous time an established leader in the video-games industry tried to bring VR to life, Nintendo - riding high on the success of its Game Boy - launched the Virtual Boy in 1995. The clunky red headset was barely on the shelves for a year before the Japanese group abandoned the project, amid complaints of headaches from its monochrome screen.
This week, it was Sony's turn to dream the VR dream.
At the Game Developers Conference in San Francisco, industry executives and gaming fans lined up to watch the PlayStation maker unveil its "Project Morpheus" VR device, only a few yards from where a Virtual Boy was on display as part of a Nintendo museum exhibit.
"VR has been a dream of many game creators ever since the computer game was created," said Shuhei Yoshida, president of Sony PlayStation's Worldwide Studios unit, referencing the classical god of dreams after whom Morpheus is named. He promised that wearers would be "so immersed in the world that the developer has created that you forget you are playing a game".
Sony is just the largest in a growing band of companies that are together betting tens of millions of dollars on virtual reality becoming a success. Microsoft is much rumoured to be among them, although Nintendo is yet to make a second attempt at VR.
Leading the charge until now has been Oculus VR, a Californian start-up that raised $75m in venture capital funding late last year. At 21, Oculus's founder Palmer Luckey is barely old enough to remember the Virtual Boy.
"My original goal was to allow myself to experience the impossible, literally - I was building prototypes for myself," Mr Luckey told the Financial Times. "Now I'm crazy enough to think that the world wants it."
Since the 1990s, the boom in mobile phones and other portable electronics has driven down the size, cost and weight of the sensors and screens necessary for VR.
Mr Luckey began building VR headsets using spare parts from the smartphones he repaired as a teenager. As friends, then friends of friends, asked him to make more, he became convinced that others would too. Oculus now employs about 100 people and this week launched a second version of its prototype for developers, which the company claims has all the "fundamental building blocks for great VR".
"The core problem has been that the technology was never ready," said Mr Luckey. "In the past, people who hadn't tried VR were more excited about it than the people who had. That's now reversed. That's a sign that the technology is finally good enough for people to care."
Sony's research and development team has slowly come to the same conclusion. Since 2010, it has been quietly experimenting with VR prototypes, most of which involved strapping the PlayStation 3's motion-sensing controller Move to its guinea pigs' heads.
Neither Oculus nor Sony is planning to release a product for consumers this year. Before they do, both must overcome persistent technical hurdles such as blurry images and feelings of nausea - and considerable scepticism at the highest levels of the games industry.
Don Mattrick, the former Microsoft Xbox and Electronic Arts executive who is now chief of social games company Zynga, was lukewarm on the business case when asked about VR in an onstage interview on the sidelines of GDC.
"There will be a lot of concept pieces," he said. "The forward-leaning tech stuff is really cool, but it's hard to break through 10m [sales] of anything. If you really want to think about sustainable economics, for most developers they need to get to those numbers."
It will be even tougher to convince consumers to buy VR devices without great games to play on them from the outset.
Nonetheless, many developers are clamouring to get their hands on the technology. Oculus has sold more than 60,000 of its $300 Rift prototype over the past year. Many of those who queued up to try Project Morpheus at GDC this week came away impressed by demonstrations that included being lowered into the ocean in a shark cage.
"When the shark came up to me, I jumped back," said David Klingler, an independent game developer from North Carolina who tested Sony's device, which connects to its PlayStation 4. "I'm not going to do that on a screen. Things like that are unique to VR."
Among the first to commit to both Oculus and Morpheus is CCP Games, the Icelandic maker of multiplayer space-epic Eve Online. Several of CCP's founders were involved in defunct 1990s VR start-ups such as OZ Interactive, and they believe the open-ended "sandbox" world of Eve's spaceships is ideal material for virtual reality.
After an Oculus-based side-project by some developers got rave reviews from fans, last year CCP assigned about 20 staff in Newcastle upon Tyne to work on a game called Eve: Valkyrie full time. In the game, the player pilots a nimble space fighter from its cockpit, shooting down enemies Top Gun-style.
Creating the title for VR devices is little different in cost to developing for the latest consoles, said David Reid, CCP's chief marketing officer, but without the well-established guidelines and pre-packaged technical shortcuts.
"That makes it very exciting and very challenging," said Mr Reid. "It is a tremendous amount of pressure to make an awesome game for them both . . . There is frankly a higher level of intensity on something like this because we are one of the prime movers in this space."
But CCP, and other early developers such as Epic Games, believe it is worth the risk.
"The entrance of Sony into the market validates the vision of Oculus that VR is not going to be a novelty hobby," Mr Reid said.
"With this generation of consoles, we have a really good chance that VR to be one of the primary revenue drivers and market movers. But there's a long way to get there."
Varying visions of virtual worlds
Virtual reality was without question the dominant theme of this week's GDC. But several different companies have varying visions of how the technology will develop.
Oculus and Sony both ask gamers to don headsets and earphones that block out the real world, offering complete immersion in the virtual. Showing a pair of images on a high-definition OLED screen brings a 3D effect to the virtual worlds within and 360-degree views mean that players can look over their shoulder, above their head or even down at the legs and feet of their digital doppelganger.
Both devices use a combination of gyroscopes, infrared LEDs placed around the headset and an external camera pointing at the player to determine where they are looking. Getting that accurate, up to the millisecond, is crucial in preventing the nausea that has plagued VR devices.
The objective is to create a sensation VR fans call "presence", when the brain is tricked into thinking that what it is experiencing is real - right down to feeling vertigo on a digital cliff edge or claustrophobia in a virtual cupboard.
"It's really that feeling of being somewhere else," says Richard Marks of Sony's VR R&D team. "There's no way to explain it . . . It's really very compelling but you have to experience it to understand what it means."
Nate Mitchell, Oculus' vice-president of product, adds: "The only other medium that delivers presence is real life."
Others technologists at GDC were demonstrating a less immersive but more sociable "augmented reality".
Technical Illusions raised $1m on crowdfunding site Kickstarter last November for castAR, a pair of geeked-out spectacles that project a hologram-like image on to special reflective surfaces. The system was an accidental discovery when former toy designer Jeri Ellsworth was working on VR at Valve, the games developer and publisher.
"Not having a screen in front of your eye, you are grounded in the world," she says, making it easier to converse with people nearby while you play. "The eye strain goes away and motion sickness is not a problem."
Meanwhile, Swedish computer-vision company 13th Lab was showcasing Rescape, in which a smartphone strapped to a toy gun turns the real world into a game of virtual paintball. Its iPhone app scans the room then recreates a digital version that superimposes enemies and fantastical environments over the real-life furniture, bringing Call of Duty out of the screen and into the living room.