Path Tracing Set To Get Faster With DXR 1.2 SER And RTX Mega Geometry Advances

Path tracing is still being worked on because it is an important part of modern graphics rendering. Its speed, standardization, and real-time improvements are still being made.

Recent talks by developers show that hardware developers and game companies are improving performance and processes, as well as finding creative and technical solutions to problems, in order to make path tracing work better in future games.

Overview of GDC Presentations

We have also watched several GDC talks, mainly on ray tracing and path tracing, including content from NVIDIA and one more section from Intel. The Future of Path Tracing was the title of the first key presentation, in which Martin Stich and Carmelo Fernandez Aguerra presented the results. The talk was split into two sections: standardization of Nvidia features in DXR and a strategy of practical implementation of path tracing.

Martin explained that DXR1.2 now includes features introduced with Ada Lovelace GPUs, such as shader execution reordering (SER) and opacity micro maps (OMMs). These characteristics enhance functionality in conditions such as foliage and transparency. Their addition to DXR means developers no longer need to use NVAPI, and it can be used by a wider range of vendors. Intel GPUs already have SER, but AMD GPUs will follow suit with RDNA5.

Future Directions for DXR Evolution

The other concern was the future of DXR, which is colloquially known as DXR2.0. A significant feature is RTX Mega Geometry, which enables working with very detailed scenes. This was demonstrated by Nvidia's work on The Witcher 4, where a new level-of-detail system enables millions of trees to be path-traced.

We notice that distant trees use OMMs to reduce the number of instances. In contrast, close geometry uses fine-grained detail in Mega Geometry. The idea is to have this system fit seamlessly into the current workflows, especially with UE5 vegetation pipelines, so developers do not notice it, and performance is not compromised. The system is undergoing optimization and will be published later.

Path Tracing in the RE Engine

Next, we watched another talk, Implementing Real-Time Path Tracing in the RE Engine by Hitoshi Mishima of Capcom and Kelvin Shu of NVIDIA. This presentation was unique because it featured first-hand observations from an internal engine developer, not just vendor perspectives.

The implementation was developed in 1.5 years by two engineers who were not dependent on their own internal reference path tracer at Capcom. The outcome drastically enhanced visual quality, but the process was both technically and artistically problematic. The engine applies ReSTIR global illumination but not ReSTIR direct illumination. The team used custom compute shader optimizations to improve coherency on the GPUs rather than using SER.

Artistic and Technical Problems

We were told that correcting the visual results required several adjustments. Guide buffers were required to avoid visual issues caused by the disappearance of rain or the lack of projected textures. In the absence of these, accumulated lighting and denoising methods might strip significant visuals.

To achieve optimal skin representation, the Ray reconstruction required additional guidance, particularly when moving from CNN-based to transformer-based models. Subsurface scattering required certain treatment as well. Perhaps one of the most challenging was ensuring the artists were satisfied, because path tracing distorted lighting compared to older methods. Engineers and artists had to work closely and continuously to produce final results.

Shader Execution Reordering and Optimization

On Nvidia's part, Kelvin Shu discussed additional optimization of path tracing in the RE Engine. The mere provision of SER did not immediately enhance performance. Actually, the simple implementation resulted in a 3ms slowdown.

With refined assumptions and reorganized workloads, the optimized version reduced path tracing cost to 3.3ms, compared to 17.7ms with no SER. Such improvements are likely to be introduced with new titles, such as Pragmata, which is expected to launch with DXR1.2 features. This could become one of the first games to fully utilize the updated API.

Future Features and Direction

Capcom outlined some planned improvements to its path tracing pipeline. These include ReSTIR direct illumination, transparent and translucent path tracing, VFX volume rendering, and neural shading. These capabilities are designed to take high-end rendering to the next level, particularly on PC platforms.

Another distinguished improvement was in hair rendering. Path traced down to the triangle level to hair. This relates to a more general argument about tracing primary visibility rays fully via path tracing rather than rasterization.

Moving Beyond Rasterization

For speed and ease of use, most path-traced games still use rasterization as their first viewing method. But this might not be the case with new gear. Whole-path-traced primary rays might make things possible like right scopes, good field-of-view management, and simple rendering pipelines that don't need two sets of data.

This shift can be seen in performance comparisons between GPU architectures. Rasterization is much faster on Turing. Ampere bridges the performance gap, and Ada Lovelace and more modern architectures play a game of rasterization versus ray tracing that is even more similar. This implies that future GPUs might prefer to have fully path-traced pipelines.

Final Thoughts

We observe that the combination of developers and hardware vendors is speeding up the implementation of path tracing. The titles that will come out in the future will venture deeper into fully path-traced rendering, with better APIs, smarter optimization, and changing hardware capabilities.