Notes

Optimizing Mobile Game Performance: RuneScape



Optimizing Mobile Game Performance: RuneScape

Lewis Gordon



RuneScape is a hugely acclaimed MMO which is currently in its 20th anniversary, and has recently been transferred from desktop computers to mobile platforms. The Galaxy GameDev team were involved from an early stage in development, profiling the game and providing optimization recommendations for the development team.



We made many suggestions during our time working with the game. The most important one was to move rendering API call to a dedicated thread (a.k.a. deferred rendering). This was in line with the RuneScape team's work to create a separate thread for rendering. It is not uncommon to find PC games to rely on a single thread which handles the main game loop and rendering, however this can be a limiting factor in framerates on mobile; the CPU was taking a lot longer to submit a frame than the GPU was taking to render it.



The main difference between a desktop computer and a mobile device, is their power requirements. Desktop PCs can be plugged into the mains power supply and draw a significant amount of power, 500W plus for gaming PCs and it can also use huge fans to keep cool. A mobile device typically relies on a battery that is small, and should be comfortable to hold, limiting the temperature it can get. To ensure a long battery life and a an ideal temperature the device should use around 3-4W of power.



Mobile CPUs are unable to achieve the same high frequency that desktop CPUs do, making it difficult to match single-threaded performance. However both mobile and desktop CPUs have had multiple CPU cores for a period of time, making it possible to distribute the load over several cores.
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The most straightforward way to break up a single threaded game is to create two threads, one for the main game and other systems, and the other to render the scene. This is the approach that Jagex took with RuneScape for mobile and it had a significant impact to performance. Framerates more than doubled in certain instances.



More sophisticated architectures employ job systems that allow certain CPU tasks such as physics and animation to be run on several cores, in addition to having separate render thread. This method is used in game engines such as UE4 and Unity.



It is important to note that multithreading can still be beneficial even if your game is running at 60fps in one thread. This is because power consumption and clock frequency are not in a linear relationship. If you run everything on one core, it will be required to operate at a higher frequency. This will result in higher consumption of power and battery drain. It may also cause the device to throttle the CPU to avoid overheating.





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