Can AMD GPU perform ray tracing

Ray tracing in games VI: Ray tracing at AMD and conclusion

What could AMD's approach look like?

In the middle of last year, AMD described an approach for real-time ray tracing in hardware that deviates from that pursued by Nvidia. The calculations for ray tracing are integrated into the texture processors of the shaders. A developer of the Xbox Series X with AMD GPU caused a surprise two months later when he spoke of dedicated RT cores at AMD, which at first glance contradicts an integrated solution. In the second, however, the combination of both worlds indicates which approach AMD will pursue with ray tracing.

The BVH algorithm requires good access to cache and VRAM with high bandwidth. As an outsourced element, as is the case with the RT core at Nvidia, this means that space is taken up by an additional storage connection. AMD describes that the texture processor, which is responsible for calling up the textures during shading, already has an optimal connection to the memory. It is therefore predestined to execute the BVH algorithm in a memory-efficient manner. The second step for ray tracing, the interface definition, is then carried out by a new processing unit, the so-called "Ray Intersection Engine". This is a fixed-function unit, i.e., like Nvidia, an ASIC that is integrated into the texture processor. This unit could be what the Xbox developer called the dedicated processing unit for ray tracing.

This is what distinguishes Nvidia's and AMD's approach

AMD's approach differs from Nvidia's approach in two ways. On the one hand, the new processing unit only carries out one instead of two steps in the ray tracing pipeline. As a result, this area can be smaller, which saves chip area. On the other hand, the scheduling, i.e. the decision as to which steps are to be taken and when, is increasingly carried out by the shader unit. The texture processor always only processes the passage of rays through a box level in the BVH and delivers the result (ray interface or other boxes that have to be passed through) back to the shader unit. This is done in the same way as textures were previously provided, and can therefore continue to use the existing infrastructure of the shaders. Then the shader unit decides which steps to take next, allowing developers better control over the computational effort required for ray tracing. The shader unit also determines how many secondary rays are to be traced.

Whether AMD's solution actually looks like the one described here and whether the consoles receive a different solution remains to be seen in the course of this year. For the upcoming graphics cards based on RDNA2, there is no more precise date than 2020. For consoles, however, it is known that they will appear at the end of the year. Also from Nvidia there should be a new generation of graphics cards this year, with improvements in ray tracing to be expected. The only thing that is certain is that they will be compatible with Microsoft DXR, which is now an integral part of DirectX 12 Ultimate.

More backgrounds in the community

Since the announcement of the RTX graphics cards, a thread by community member ZeroZerp has been devoted to the discussion about the new technology. In addition to a list of all announced games with ray tracing support, there are also countless videos with demos of the new technology and presentations by the developers that go into great detail. The topics include optimizing ray tracing and the implementation of completely new effects that have never been displayed before, such as soft shadows that adapt to the roughness of the subsurface.

Conclusion

In 2007, Raytracing was reported intensively for the first time on ComputerBase. Since 2018, this technology has finally been supported in hardware and implemented in games. In order to enable the hybrid approach of simultaneous rasterization and ray tracing, the architectures of graphics cards must be significantly expanded and adapted. What is known so far has been summarized in this article. To what extent ray tracing will develop further this year with new releases on the hardware front remains to be seen. The question of how many games with ray tracing will be added in the next few years also remains open. One thing is certain: the technology undoubtedly belongs to the future, you just have to be able to calculate it efficiently. The next consoles should take a good step forward on this point as well.

Was this article interesting, helpful, or both?The editors appreciate every support from ComputerBase Pro and deactivated ad blockers. More about advertisements on ComputerBase.

  • Christoph Riedel Email
    ... writes about the current research and development of current and future technologies in the field of GPU and CPU.