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Nintendo shares its tricks for reducing latency on Wii U's GamePad

Minimizing wireless latency is critical for Wii U's GamePad tablet. Nintendo's R&D team shares how it reduced latency and made it possible for devs to use the controller for second-screen gameplay.
Minimizing wireless latency is critical for Wii U, as the console's GamePad tablet controller needs to display gameplay that matches what's on TV screens, without any noticeable delay. "[We] had to take on a challenge that no one else had before," said Nintendo head Satoru Iwata in a roundtable discussion with the company's R&D team. "With the usual wireless video transfer methods, even if a slight latency occurred, it was okay as long as it didn't get stuck along the way. "So with ordinary video playback, [when the flow of data is interrupting smooth playback,] the system buffers a certain amount of data before it plays... With the Wii U GamePad, however, Mario has to jump as soon as you press the button. So if there's latency, it's fatal for the game." Nintendo's Product Development Department employed a variety of tricks to reduce latency. For example, traditionally when sending video wirelessly, a single-frame of image data is compressed, sent and decompressed at the receiving end, then displayed on a screen. "We thought of a way to take one image and break it down into pieces of smaller images," said the team's Kuniaki Ito. "We thought that maybe we could reduce the amount of delay in sending one screen if we dealt in those smaller images from output from the Wii U console GPU on through compression, wireless transfer, and display on the LCD monitor." He adds, "Generally, compression for a single screen can be done per a 16x16 macroblock. And on Wii U, it rapidly compresses the data, and the moment the data has built up to a packet-size that can be sent, it sends it to the Wii U GamePad." This solution worked out particularly well for the team because it solved multiple problems -- it not only minimizes latency by reducing the amount of data that needs to be buffered before sending out the data, this method requires less memory and less power consumption than traditional techniques. The team notes that it was able to reduce latency with this technique and other tricks to the point where images can be transmitted and displayed on the GamePad faster than some TVs connected to a Wii U with a cable, because many newer TVs have latency due to their video processing components. Michel Ancel, who is leading development on Rayman Legends for Wii U, recently praised the system's GamePad in an interview with Nintendo Power: "The response time is crazy, in fact, and I think the competitors will need some time to [get their controls] this responsive. "It's crazy because the game is running in full HD [on the television], we are streaming another picture on the GamePad screen, and it's still 60 frames per second. The latency on the controller is just 1/60 of a second. ... It's almost instant. That’s why it responds so well. So it can be used as a real game-design thing."

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