Tech Focus: IMG on PowerVR mobile graphics

IMG talk graphics tech featured in iPad 2 and Sony NGP

Feature by Richard Leadbetter Technology Editor, Digital Foundry

Published on April 13, 2011

Weeks on from the iPad 2 launch, the full graphical power of the new tablet is finally coming into focus - and it's frankly monstrous, a massive statement of intent from Apple on its plans for the games market.

Apple's new A5 processor features a dual core PowerVR SGX 543 – the same graphics tech that's set to be featured in the forthcoming Sony NGP, the difference being that the new PlayStation portable will double the core count, bringing an unprecedented amount of graphical power to the mobile space.

UK-based Imagination Technologies is the engineering force behind the PowerVR graphics tech: in this interview, director of PR David Harold and business development manager Kristof Beets talk frankly about its current range of mobile processors and their capabilities, the importance of its support for DirectX and Open GL standards and discusses some of the custom features found in their GPUs. They also go into depth on the scalability of their hardware and look forward to the emergence of the ARM-based version of Windows.

Finally, if you thought the performance increase between the iPad and iPad 2 GPUs was impressive, the final question we put to Imagination should help put some perspective on that...

Digital FoundryWhat are the key rendering differences between the PowerVR architecture and the approach taken by NVIDIA and AMD?

IMG

PowerVR graphics technology is based on a concept called Tile Based Deferred Rendering (TBDR). In contrast to Immediate Mode Rendering (IMR) used by most graphics engines in the PC and games console worlds, TBDR has two components, the first Tile Based Rendering which focuses on keeping data processing on-chip by breaking the screen down into manageable tile sized chunks which can be kept on chip.

The second part focuses on minimising the processing required to render an image as early in the processing of a scene as possible, so that only the pixels that actually will be seen by the end user consume processing resources. This approach minimises memory bandwidth and power consumption while improving processing throughput but it is more complex.

Digital FoundryA lot of people have tried to bring a TBDR solution to market, but only IMG has achieved it. Why do you think the mainstream GPU manufacturers have stuck to their traditional approaches?

IMG

Partly because although the idea sounds simple it's actually very hard to do it in practice - especially in such a way that looks like any other renderer to developers. Partly because we have a lot of the fundamental patents.

Digital FoundrySGX543 is described as a Shader Model 3 part. This is a DirectX standard, but DX doesn't apply to the mobile devices. In contrast the PICA200 in the Nintendo 3DS forgoes PC style design for a design targeting intended use in a handheld. What are the costs and advantages going with a standard born in the PC space?

It's essential to understand that standardisation is critical for mass market success since standards enable content and without content hardware is of no use.

IMG

We target a range of markets from phone through navigation to computing and TV. We aren't a "PC style design" but we do on some of our cores offer DX capability for the computing market - and now for future Windows based mobile devices.

The total Series5 and Series5XT portfolio enables the industry's broadest range of performance/area options, from the smallest single pipe SGX520 core up to the 64-pipe SGX543 MP16. All popular APIs and OS are supported by all SGX cores, including OpenGL ES 2.0/1.1, OpenVG 1.1, OpenGL 2.0/3.0 and DirectX 9/10.1 on Symbian, Linux, Android, WinCE/Windows Mobile and Windows 7/Vista/XP.

It's essential to understand that standardisation is critical for mass market success since standards enable content and without content hardware is of no use. The highly proprietary approach taken by PICA200 can only work in a closed console environment and even there will limit content availability.

Imagination is focused on supporting key industry standards and for mobile parts this is focussed on Khronos APIs such as OpenGL ES but also increasingly the mobile market is crossing over with the PC market with tablet and netbook designs using the same processors and obviously this introduces the requirement for Microsoft DX API support. Also with game engines originating from the PC market coming down into the mobile space, such as the Epic Game Unreal engine, support and compatibility with PC functionality becomes increasingly important as standards and requirements evolve.

Digital FoundryGiven scalability and DirectX based features, will IMG be more actively targeting PC use in future such as netbooks or even desktops? We've not seen much from you since Intel licensed SGX535 for GMA500/GMA600. What about consoles and CE devices?

IMG

We already do pretty well in netbooks with devices from Asus, Acer, Sony etc. We also now have a higher end technology for the professional market from Caustic, a new part of Imagination. The scalability of forthcoming PowerVR cores should make them very suitable for the rest of the computing market too. However there's a gap between what we have as licensable IP and what our customers decide to do with that IP.

As Windows moves more into mobile and embedded devices due to our experience we are uniquely positioned to support DX (irrespective of the CPU architecture).

Digital FoundryThe PC graphics architecture space has been defined over the past decade by DirectX, and proprietary features of IHV designs have gone largely unexploited. Do you feel this is a good thing for standardisation, or a bad thing limiting innovation?

IMG

We believe in open standards, such as DX and OpenGL ES and are very active helping define those standards, working with Microsoft and as a promoter member of Khronos. We do expose some proprietary features via extensions though. When it comes to proprietary features it all depends on what they add for users whether they get used.

For example our 2bpp texture compression is very widely used, because it delivers high quality and real efficiency benefits but also for distribution size and memory footprint. It's a thin line to walk between true benefits that developers are eager to use and over-fragmentation of the market which damages developer uptake. For this reason we regularly survey our ecosystem partners to determine their true requirements and interests.