We describe a method of game streaming, the Geometry Pump Engine Group protocol, We describe a method of game streaming, the Geometry Pump Engine Group protocol, designed to address the limitations of video-based cloud gaming and command streaming approaches. It produces a true content stream of sub-assets with adaptive scalability and intelligent caching.
Barry L. Jenkins, John Scott, Francois Malassenet, and Kshitij Patil, Concurrents
Article Excerpt -
Although video-based cloud gaming systems have been available for more than a decade,1 quality, cost, and scalability issues have generally limited their adoption. Command
streaming is a proposed alternative to cloud gaming that is designed to lower costs and improve scalability. In this article, we examine the technical challenges of video-based cloud gaming and command streaming systems. We introduce a new method of game streaming, called subasset streaming, designed to address the limitations of both systems.
While it can be argued that the business models adopted by cloud gaming companies have often led to a suboptimal product–market fit, this article focuses only on the technical challenges of making game engine con- tent instantly accessible from the cloud for games and other high-fidelity 3D interactive applications. Our work makes the following contributions: 1) a method of conservative from-region visibility precomputation, 2) a method of submesh clustering and texture tiling capable of supporting granular visibility-based prefetch, and 3) an application programming interface (API) for the navigation-driven, visibility-based prefetch of subassets, enabling efficient game streaming at zero latency and without compression artifacts. The practical limitations of video-based cloud gaming systems are in many ways a consequence of the apparent simplicity of the approach: for every user, run the game in the data center and send the resulting video.
Unfortunately, games tend to be one of the most resource-intensive consumer applications, and few commodity servers can run them. Video-based cloud gaming systems require specialized servers that include a GPU, multiple CPU cores, and a relatively large amount of random-access memory (RAM) dedicated to every concurrent user.
As a practical matter, video-based game services locate these specialized servers in regional data centers. This centralization can exacerbate another weakness of video-based cloud gaming systems: latency.With the requirement of specialized servers, it is extremely challenging to use typical edge computing and distributed content delivery network (CDN) strategies to reduce the latency inherent in sending real-time video in a cost-effective manner. The need to send video frames in real time makes these systems very sensitive to jitter and packet loss since there is little if any playout buffer and no time for retransmission error correction. These issues are aggravated at targeted rates of 90–144 frames/s, which are required for virtual reality content and other- wise used by an increasing number of gamers to experience better responsiveness and performance.
Video-based cloud gaming systems can also compromise image quality through excessive compression. While native gaming devices typically employ no compression between the GPU and display, video-based cloud gaming systems depend on compression to deliver frames over broadband. They also typically employ significantly lower quality video compression profiles than those used by video-on-demand systems that stream preencoded video. While preen- coded video can achieve higher quality compression by using high-latency encoding methods, such as B-frame encoding, video-based cloud gaming systems cannot leverage this approach without introducing unacceptable latency.
Because of these frame pacing, latency, and compression issues, video-based cloud gaming systems typically provide a quality of experience that can be significantly lower than playing a game on a PC or console.How- ever, since video-based cloud gaming systems enable users to play on devices, including phones and tablets, that are not capable of running the games natively, the reduced quality of experience can be an acceptable tradeoff for some users, particularly when playing at lower resolutions and frame rates.
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