What you’ll learn:
- Why ray tracing is important on mobile.
- How Imagination’s CXT family delivers level 4 ray-tracing capabilities.
Imagination Technologiesis well-known for pushing the limits of GPUs, and its new CXT family continues this trend. One of the key features of this GPU IP is level 4 ray-tracing hardware support. At this point, ray tracing is a feature found on high-end systems that target gaming and video editing.
Ray tracing replicates real lighting and shading based on reflections and refraction of light(Fig. 1)。此过程是数据和计算密集型的，但提供了逼真的图像。它还提供了我们通常不知不觉地注意到的视觉提示，这些提示通常不会在比特映射成像中复制，通常用于减少处理和存储开销。
There are five levels associated with ray-tracing hardware:
- Software using traditional GPUs
- Ray-box and ray-triangle testers
- Bounding-volume-hierarchy (BVH) processing in hardware
- BVH支持加上硬件中的相干分类
- Coherent BVH processing with BCH hardware builder
通过此射线追踪级别系统（RTL）可以将其转移到硬件中，越好，因为它可以提高性能并减少功率要求。缺点是需要更多的晶体管使其正常工作。NVIDIA’sRTX 8000与射线跟踪支持is almost three years old, but that and subsequent hardware has been sitting on PCI Express cards for PCs and servers. Attaining this type of performance on mobile hardware is a bit more challenging.
想象力追踪支持的基础是光子射线加速群（RAC）(Fig. 2)。这开始with a box tester unit (BTU), a dual triangle tester unit (DTTU), and a procedural tester unit (PTU) that searches for rays intersecting with an object in 3D space. This hardware tests rays against axis-aligned boxes from the 3D scene hierarchy. It effectively implements level 2 support.
The addition of the box primitive scheduler (BPS), ray reference courier (RRC), ray store (RS), and ray task scheduler (RTS) brings the hardware up to level 3 RTLS. These dedicated blocks keep the ray date on-chip, and it handles ray traversal, tracking, and monitoring.
The packet coherency gather (PCG) block brings the RAC up to level 4 RTLS. It analyzes all active rays and creates groups of coherent rays. These can be tested together against the 3D scene.
A single RAC can handle 433 Mrays/s and 16 Gbox-tests/s. The hardware supports the VulkanRT ray-query and ray-pipeline interfaces. It works on all ray-traced content and enables advanced ray-tracing effects on a mobile power budget.
The CXT RT3 combines three Photon RAC blocks with other GPU blocks, including Tensor Processing Units (TPUs) and Unified Shading Clusters (USCs). Multiple CXT RT3s can be combined as well(Fig. 3)。这只是显示了使用GPU多少个不同的任务。CXT RT3可以以1080p的速度传递30到60帧/s的射线跟踪内容。
Expect mobile devices like smartphones to make even better use of their hi-res displays. This moves mobile gaming and user interfaces to a new level.
Imagination provides developers with tools like PVRTune, which can examine low-level ray-tracing counters built into the hardware.
