Allgemein AR/VR Basics Gaming GPUs Reviews

Nvidia GeForce RTX 2080 Ti and RTX 2080 unveiled – what turing really is all about

Beyond what volta is concerned and arguably the most promising chapter in the entire Turing story, the RT core is anchored to the bottom of each SM in TU102. Nvidia's RT cores are essentially pure accelerators with a fixed "pre-wired" function for the evaluation of cross and triangular sections of the Bounding Volume Hierarchy (BVH). Both operations are essential for the ray tracing algorithm.

In short, these BVH form boxes with geometry content in a particular scene. These boxes help to narrow the position of triangles that cut rays through a tree structure. Each time a triangle is in a box, it is divided into several additional boxes until the last box can be divided into triangles. Without BVHs, an algorithm would be forced to search the entire scene by burning tons of cycles that test each triangle for a possible crossing.

This algorithm is now possible with the Microsoft D3D12 Raytracing Fallback Layer APIs, which use Compute Shadern to emulate DirectX Raytracing on devices even without native support (and redirect to DXR when driver support is supported recognized). On a Pascal-based GPU, for example, the BVH scan is performed on programmable cores that pick up each box, decode it, test for intersections, and determine if there is another, subordinated box or triangle inside.

The process repeats until triangles are found where they are tested for intersections with the beam. As you can imagine, this process is very hardware-killing in its execution as pure software emulation, so that a smooth flow of real-time ray tracing on today's graphics processors is almost prevented.

By creating such fixed-function accelerators for the intersection steps between the box and triangle, the SM throws a beam with a Ray-Generation shader into the scene and passes this structure to the RT core. All intersection evaluations are of course much faster and the other resources of the SM are released for shading, just like with a traditional rasterization.

According to Nvidia, a GeForce GTX 1080 Ti with its CUDA cores, which provide 11.3 FP32 TFLOPs, can process about 1.1 billion beams per second into software. In comparison, the GeForce RTX 2080 Ti with its 68 RT cores can process about 10 billion beams per second. It is important to note that none of these numbers are based on calculated peaks. Instead, Nvidia took the geometric mean of the results from multiple workloads to set itself to the value of "10+ Gigarays".

But Ray Tracing is a very broad term in itself, because only the pursuit of a ray says not much. What is more important is what can be implemented with the help of these functions. because the information thus obtained can be used very versatile to create things like AO, Reflections, Global Illumination and much more. improve or/or make it possible in the first place.

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About the author

Igor Wallossek

Editor-in-chief and name-giver of igor'sLAB as the content successor of Tom's Hardware Germany, whose license was returned in June 2019 in order to better meet the qualitative demands of web content and challenges of new media such as YouTube with its own channel.

Computer nerd since 1983, audio freak since 1979 and pretty much open to anything with a plug or battery for over 50 years.

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