Dynamic Ray Traversal Order Using Hit Tokens
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Solution Overview
Problem
Conventional ray tracing techniques are computationally expensive due to the high number of ray intersection tests required, and they do not effectively exploit temporal and spatial coherence between rays, leading to inefficient performance.
Innovation Solution
The proposed solution involves using a bounding volume hierarchy and hit tokens to reorder node traversal based on temporal and spatial similarity between rays, reducing the number of acceleration structure nodes traversed and improving performance by selecting optimal starting nodes for subsequent ray traversals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ray tracing techniques are used with standard node traversal, then ray intersection tests can be performed, but the computational cost is high due to the large number of tests required
Solution Approach 1:
The patent applies preliminary action by pre-sorting acceleration structure nodes based on temporal coherence (using hit tokens from previous frames) and spatial coherence (using ray origin and direction similarity) before ray traversal begins. This pre-ordering allows subsequent rays to start traversal from optimized starting nodes, reducing the number of intersection tests needed while maintaining rendering accuracy.
2Productivity
If the number of ray intersection tests is reduced by optimizing node traversal, then rendering efficiency improves, but the complexity of the traversal algorithm increases
Solution Approach 1:
The patent applies dynamics by making the node traversal order adaptive and variable rather than static. The traversal starting node is dynamically selected based on hit tokens from previous frames and spatial coherence calculations for each ray packet. This dynamic adaptation reduces the number of intersection tests needed while the complexity is managed through systematic coherence exploitation rather than arbitrary complexity.
3Productivity
If temporal and spatial coherence between rays is exploited to reorder node traversal, then the average number of intersection tests per ray decreases, but additional data structures and processing are required
Solution Approach 1:
The patent applies copying by using hit tokens that copy intersection information from previous frames and rays. Instead of performing full intersection tests, the system copies and reuses traversal state from temporally and spatially coherent rays, significantly reducing the number of actual intersection tests while managing complexity through efficient token-based state representation.
4Productivity
If optimal starting nodes are selected for subsequent ray traversals based on coherence, then rendering performance improves, but memory usage increases to store traversal state
Solution Approach 1:
The patent applies local quality by storing traversal state and hit tokens only for rays and nodes that exhibit temporal and spatial coherence, rather than maintaining state for all possible rays. This localized storage approach optimizes memory usage by focusing resources on coherent regions where reuse provides the greatest performance benefit, while avoiding unnecessary memory consumption for incoherent rays.
Data Source
AI summary
Devices and methods for node traversal for ray tracing are provided, which comprise casting a first ray in a space comprising objects represented by geometric shapes, traversing, for the first ray, at least one first node of an accelerated hierarchy structure representing an approximate volume of a group of the geometric shapes and a second node representing a volume of one of the geometric shapes, casting a second ray in the space, selecting, for the second ray, a starting node of traversal based on locations of intersection of the first ray and the second ray and an identifier which identifies one or more nodes intersected by the first ray and traversing, for the second ray, the accelerated hierarchy structure beginning at the starting node of traversal.