Videos posted to social media of the FlexPai in action, however, indicate the version of Android they run still needs some work.
In particular, the display is shown to flick between different orientations after being switched from one mode to another before settling.
Purchasers will also need to be mindful that the device weighs 320g – more than 50% more than the iPhone XS Max or Galaxy Note 9.
However, Royole says the FlexPai has been tested to withstand more than 200,000 open-and-shut movements, meaning it should offer many years of use before the action damages the picture.
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One expert said the smartphone was unlikely to become a bestseller but was impressive nonetheless.
“Royole gets the bragging rights to being first, and it’s quite astonishing that someone you’ve never heard of is doing this,” said Carolina Milanesi, from the Creative Strategies consultancy.
“What’s great is that it’s putting this into the hands of developers, who will be able to start the legwork that will result in apps for flexible devices that will eventually be sold by Samsung and whoever else.
“You need developers to think through how they can best take advantage of screens that double in size.”
She added that Royole might ultimately become an acquisition target for one of the mainstream consumer electronics brands.
Another company-watcher added that he doubted the FlexPai would ever be produced in large numbers.
“Royole has carried out several publicity stunts over the years to showcase its flexible OLED [organic light-emitting diode] displays,” said Dr Guillaume Chansin from Irimitech Consulting.
“The FlexPai is probably another stunt.
“Royole is building its first OLED factory and it is now trying to compete directly with other display manufacturers such as Samsung and LG.”