Mobile GPUs lag desktop GPUs by many years in terms of features, so they aren’t always conducive to exciting news coverage. However, hardware Ray-Tracing (RT) on an ARM GPU design is a milestone worth noting.
In its new Immortalis-G715 (cool name btw) graphics unit, ARM delivers a 300% performance improvement over the previous software solution at the cost of 4% of the shader core area. It seems like a very reasonable number for a feature that isn’t widely used in mobile games.
As such, it seems prudent for ARM to introduce a hardware feature that developers can test. Meanwhile, the cost to OEMs and end-users remains limited. The I-G715 will also serve as an excellent platform for drivers and Graphics APIs teams to further validate their work.
Finally, there will be a great deal of scrutiny to see how the architecture performs with the first round of apps.
ARM also added VRS (Variable Rate Shading). This feature lets graphics programmers define areas of the screen that could be rendered at half or quarter resolution because there aren’t any remarkable details (like smoke, fog, etc). Although not directly related to Ray-Tracing, VRS can help the overall performance and help introduce ray-tracing as a small part of the general frame rendering.
The critical piece of information that we don’t have is how many rays can be cast per second. I’ll just assume that the acceleration structure is efficient, but we don’t know either. ARM has shown a demo in which you can see a “with vs. without” Ray-Tracing scene.
If that’s the case, the Ray-Traced scene features transparency, reflections, and shadows, three elements that tend to benefit first from ray-tracing compared to rasterization. Although I find the difference artificially exaggerated, it’s a decent way to explain what RT is about, especially to the non-expert.
Remember that scenes, including actual PC games, aren’t typically rendered completely using RT, but the above aspects I listed are generally part of early basic RT demos.
Given the relative lack of softness of the shadow and that reflection/refraction consumes fewer rays, I’d say that performance is not high, nor was it expected to be. The camera was also static, so I’m not sure everything gets re-rendered every frame. Again, this might also be due to performance and would be a classic demo trick.
Without soft shadows, and global+dynamic lighting, it’s hard to gauge if ARM has nailed the most essential part of modern hardware ray-tracing: the de-noising. Perhaps that could be the topic of further investigation or inquiry in the future.
The ray-tracing power efficiency might be higher than a PC GPU. That would be something ARM might want to communicate about (if remarkable).
Fortunately, many game developers have experience with RT on PC, and some of their workflows have worked out. Don’t expect a lot of flashy effects on mobile just yet, but I can tell you that nothing will stop the arrival of ray-tracing on mobile. It is inevitable.
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