HART: A Hybrid Architecture for Ray Tracing Animated Scenes

Abstract

We present a hybrid architecture, inspired by asynchronous BVH construction [1], for ray tracing animated scenes. Our hybrid architecture utilizes heterogeneous hardware resources: dedicated ray-tracing hardware for BVH updates and ray traversal and a CPU for BVH reconstruction. We also present a traversal scheme using a primitive's axis-aligned bounding box (PrimAABB). This scheme reduces ray-primitive intersection tests by reusing existing BVH traversal units and the primAABB data for tree updates; it enables the use of shallow trees to reduce tree build times, tree sizes, and bus bandwidth requirements. Furthermore, we present a cache scheme that exploits consecutive memory access by reusing data in an L1 cache block. We perform cycle-accurate simulations to verify our architecture, and the simulation results indicate that the proposed architecture can achieve real-time Whitted ray tracing animated scenes at 1,920 × 1,200 resolution. This result comes from our high-performance hardware architecture and minimized resource requirements for tree updates.

A Survey on Bounding Volume Hierarchies for Ray Tracing

“…Aside from BVH construction, other notable works include the HART mobile ray tracing GPU [NKP ∗ 15], which features a hardware accelerated BVH refit unit, while relying on a CPU for the initial construction of the BVH. Woop included a HW refitting unit for B‐KD trees in the DRPU architecture [Woo06].…”

An Implementation of Multi-Chip Architecture for Real-Time Ray Tracing Based on Parallel Frame Rendering

“…Later, Viitanen et al presented two faster BVH construction architectures named MergeTree [35] and PLOCTree [36], which are based on the newer BVH construction algorithms (HLBVH [37] and PLOC [38]). Second, HART [16] is a heterogeneous system for hardware-accelerated BVH refitting and CPU-based BVH construction. This is possible by extending the asynchronous BVH construction [17].…”

“…First, the AS, such as a kd-tree or bounding volume hierarchy (BVH), is essential for ray-tracing acceleration [14], [15]. Second, for dynamic scenes, the AS should be re-built or be asynchronously built at every frame [16], [17]. Third, because a tree build algorithm based on the SAH (surface area heuristic) has an N log N complexity and is recursive, it is normally difficult to achieve scalable performance improvement via parallelization [18], [19].…”

Load Balancing Algorithm for Real-Time Ray Tracing of Dynamic Scenes

“…Tree quality can be adjusted in many ways [19], including setting a tree's depth to a certain value, establishing the volume of each leaf node by using the max primitive number, and changing the K T , K I values in (1) [6]. The present research adopted the adjustment of the max primitive number, which is a universal method.…”

“…Although waiting is not necessary under asynchronous operation, the slowing down of treebuilding owing to a given scene potentially diminishes tree quality; if scene topology changes, a rebuild is needed, which may result in waiting time [5]. The cost of tree-building and the resulting waiting time can be reduced through the construction of a shallow tree using axis-aligned bounding boxes (AABBs) of each primitive [6]. However, this method involves the use of fixed tree-building parameters, which in the end can cause waiting time depending on the scene being rendered.…”