Notes

Optimizing Mobile Game Performance: RuneScape



Optimizing Mobile Game Performance: RuneScape

Lewis Gordon



RuneScape is a hugely popular MMO, now in its 20th anniversary, and has recently been ported from desktop computers to mobile platforms. The Galaxy GameDev team were involved from an early stage in development, profiling the game and recommending optimisation suggestions for the development team.



We made a variety of suggestions over the time we were supporting the game, the most significant was the recommendation to move rendering API calls to an individual render thread (a.k.a deferred rendering). Extrememining This was in keeping with the RuneScape team's efforts to develop an entirely separate thread for rendering. It is not unusual for PC games to use one thread to handle the main game loop and rendering, but this can be a limiting factor for framerate on mobile; the CPU was taking longer to submit frames than the GPU was taking to render it.



The major difference between a desktop computer and a mobile device is the power demands for each. Desktop PCs can be connected to mains and draw a large amount of power, up to 500W plus for gaming PCs, and also have large fans to keep cool. A mobile device typically relies on a tiny battery and should be comfortable to hold, limiting how hot it can get. To ensure long battery life and comfortable temperature the device should consume around 3-4W of power.



This means that mobile CPUs can't attain the high frequency of desktop CPUs which makes it difficult to achieve the single-threaded speed. However both mobile and desktop CPUs have had multiple CPU cores for a period of time, allowing it to spread the load across several cores.



A simple architecture to break the single threaded program is to create two threads one for the primary game, one for other systems, and another that renders the scene. Jagex implemented this method with RuneScape mobile. It resulted in a massive improvement in performance. In some instances framerates have more than doubled.



More sophisticated architectures employ job systems to split up specific CPU tasks like physics and animation to be run on several cores. They also have a separate render thread. This approach can be found in game engines such as UE4 and Unity.



It is worth noting that multithreading could be beneficial even if you play at 60fps using only one thread. This is due to the fact that power usage and clock speed don't have an unidirectional relationship. If you run everything on one core, it will need to operate at a higher rate. This will result in a higher energy consumption and battery drain. It may also cause the device to throttle the CPU to prevent it from overheating.





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