ARM Community: Lighting on mobile - something to keep your eye on - ARM Community

The quality of graphics on mobile is rapidly closing in on that seen on consoles. This is a surprising feat when you consider that there are two orders of magnitude difference in power consumption between them! This is due in part to mobile graphics not merely imitating console graphics, but rethinking old problems in new ways. All real time graphics are concerned with power efficiency, but it is in mobile, where power is at the greatest premium, that we are seeing the most power efficient ways to achieve the same high quality. Mobile graphics is a battleground with a lot of bleeding edges.

At Geomerics we have been keeping a close eye on these developments, and decided last year that the time was right to support mobile devices in our flagship graphics technology, Enlighten. Geomerics delivers cutting-edge graphics technology to customers in the games and entertainment industries. Enlighten is our suite of real time lighting technologies for top-end games development, and is behind the lighting in AAA titles including Battlefield 3, Need for Speed: The Run, Eve Online and Quantum Conundrum. Enlighten offers real time radiosity lighting on all major consoles, and now ARM-based mobile devices, including popular iOS and Android tablets and smartphones.



The key technology in Enlighten is its ability to compute radiosity lighting in realtime. Radiosity lighting models a vital interaction between geometry and lights. In the real world, when a light shines on a surface a portion of this light is absorbed and re-emitted back into the scene. This bounced light will then strike another surface and so on until all the bounced light in the scene has been absorbed. This process produces soft natural lighting, and because the bounce light picks up the colour of the surfaces in the scene, it naturally ties the lighting and geometry together: A room with a red wall will gain a warm tint, while a room with a blue wall will appear cool.


Radiosity lighting is tricky to model but essential to get right – it is the element that makes lighting natural and believable. At present, the typical approach to this problem on mobile is to never move your lights during the game. As long as nothing ever changes, you can do all the lighting calculations offline and save the results in lightmaps. This ensures you will get efficient and high quality lighting in game, but it is inherently inflexible. What do you do if you want to change the time of day? Or shoot out a street light? Or turn on a flashlight? After all, interactivity is what games are all about!

For believable high quality lighting, you need to tackle the problem head on. Enlighten contains a unique and highly optimised runtime library that generates lightmaps of bounce lighting in real time. The lightmap generation occurs on the CPU and is simply added to the rest of the direct lighting on the GPU. This approach can be further combined with lightmaps generated offline, so only the lights that need to move incur any runtime cost. Enlighten includes an extremely efficient offline lightmap “baking” tool for just this purpose, where it has the added advantage of allowing you to preview the end result in real time. We strongly believe in building tools that provide fast iteration and put the artist in full control.

While porting Enlighten to mobile, Mali^TM was one of the first GPU devices we turned to. Our device of choice, a Samsung Tab 7.7, has a Mali-400 MP4 and is one of the highest performing mobile GPUs available, particularly when you consider the screen has a 720 HD resolution. At the time of writing, the most expensive part of rendering dynamic lighting on mobiles is not Enlighten, but the creation and use of shadow maps for dynamic shadowing of the direct lights. On Mali we were able to render a surprisingly large 2048x2048 shadow map for the sun and still maintain a stable 30 fps frame rate.



We can safely expect the rendering performance of mobile GPUs to become substantially faster in the near future. In practical terms this will enable more detailed lighting, closing the gap with console graphics and encouraging more dynamic and immersive games. Apart from the inevitable advances in hardware, we should also see advances in software as we better understand how to rethink rendering for mobile devices, and adapt the graphics APIs to reflect this.

Guest Partner Blogger:
Sam Martin, Head of Technology, Geomerics, he is a games middleware company responsible for the real time lighting technology, Enlighten. Their technology can be seen in Battlefield 3, Need for Speed: The Run, and Eve Online among many other AAA titles. In his current role, Sam works on expanding and developing the Enlighten product suite, while considering new technologies and research suitable for use in the games and graphics industry. Prior to Geomerics, Sam worked as a game developer across a range of titles from Lionhead, Intrepid and Kuju, building novel technology from within.

ARM welcomes its wealth of Partners in the ARM Connected Community (CC) to submit guest blogs to be published on our multiple community blogs. If interested in participating please submit email inquiries to Tell.Us@arm.com.

The ARM Connected Community (CC) is an extensive ecosystem covering all aspects of ARM processor-based design, from chip implementation through to system and device design. The CC provides a platform for collaborative innovation, with multiple types of forums for members to work with one another, and with customers, to solve industry challenges, all with the purpose of enabling designers to focus on differentiating features and an accelerated time-to-market for ARM powered solutions.