# RT Engine: An Efficient Hardware Architecture for Ray Tracing
###### Abstract
A ray query is sent from the streaming multiprocessor (SM) to the RT Core. The RT Core uses dedicated evaluators to test each ray against the box or, at the leaves of the tree, the triangles that make up the scene. It does this repeatedly, optionally keeping track of the closest intersection found. When the appropriate intersection point is determined, the result is returned to the SM for further processing. In 2021, Imagination added the Ray Acceleration Cluster (RAC) of the PowerVR Photon architecture to the C-series GPU to provide ray tracing IP technology for the mobile phone market [15]. RAC uses a highly parallel Dual Triangle Tester Unit to improve the efficiency of hardware computing. Its primary function is to perform the intersecting test of the two triangles simultaneously and send the processing results to the next stage. This series' GPU is divided into single-core and multi-core models applied to mobile and beyond mobile configurations. In recent years, dedicated hardware has also been widely referenced in ray tracing studies. SaarCOR [16] is a ray tracing pipeline consisting of a ray generation/shading unit, a four-wide SIMD traversing unit, a list unit, a transformation, and an intersection test unit. The T&I engine [17] is a hardware acceleration architecture of ray traversal and intersection tests. This architecture adopts an order depth-first layout method to reduce memory bandwidth. It proposes the three-phase ray-triangle intersection and a latency hiding architecture defined as the ray accumulation unit. SGRT [18] is a real-time mobile ray tracing GPU. It mainly includes two key features: (1) an area-efficient parallel pipelined traversal unit; (2) flexible and high-performance kernels for shading and ray generation. RayCore [19] mainly includes ray-tracing units (RTUs) based on a unified traversal and intersection pipeline and a tree-building unit (TBU) for dynamic scenes. HART [20] utilizes hetero geneous hardware resources: dedicated ray-tracing hardware for BVH update and ray traversal and a CPU for BVH reconstruction. It also uses PrimAABB for traversal scheduling. [PERSON] et al. [21] optimized the SGRT [18] and proposed two-AABB traversal architecture with two ray-AABB testing units. The experimental results showed that two-AABB was up to 2.9 times faster than the single-pipeline architecture. [PERSON] et al. proposed STRaTA (Streaming Treelet Ray Tracing Architecture) [22] to decrease energy consumption on massively parallel graphics processors. [PERSON] et al. applied MBVH (Multi Bounding Volume Hierarchy) [23] to a fixed-function ray tracing accelerator architecture. With primary rays, energy efficiency improves by 15% and performance per area improves by 20%. Another implementation approach is multiple streams, such as a different approach to hardware-accelerated ray tracing, which begins by modifying the order of rendering operations, proposed by [PERSON] et al. [24]. The dual steaming approach organizes the memory access of ray tracing into two predictable data streams. [PERSON] et al. [25] introduced Mach-RT (Many Chip-Ray Tracing), a new hardware architecture used to accelerate ray tracing. The primary approach combines a ray ordering scheme that minimizes access to the scene data with a sizeable on-chip buffer acting as near-computer storage spread over multiple chips. From the perspective of existing academic research results and commercial GPUs, ray tracing acceleration has gradually improved computing capabilities with the algorithm's progress and industrial technology's development. Due to the different algorithms adopted by different designs and the various purposes of the ray tracing hardware architecture, many strategies have considerable differences in performance and hardware resource overhead. However, they have some performance/area limitations, and we are focusing on a more efficient hardware architecture for ray tracing. Our main contributions to the literature are as follows:  
1.