Cross-Instance Front-to-Back Traversal for Ray Tracing
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Solution Overview
Problem
Ray tracing in heavily-instanced scenes faces inefficiencies due to the need for recursive depth-first traversal across overlapping instances, leading to increased traversal steps and intersections, especially when using a two-level acceleration structure.
Innovation Solution
Implement a cross-instance front-to-back traversal scheme that disambiguates hit points by using a tuple of distance and unique hit point ID, allowing traversal units to prioritize nodes based on an absolute order, even if they belong to different instances, thereby reducing unnecessary traversal operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If recursive depth-first traversal is used across overlapping instances in heavily-instanced scenes, then complete scene coverage is achieved, but traversal steps and intersections increase significantly
Solution Approach 1:
The patent segments the traversal process by introducing instance IDs and hit point IDs to uniquely identify and differentiate hit points across overlapping instances. This segmentation allows the traversal to efficiently distinguish between different instances and their respective hit points, reducing redundant traversal steps while maintaining complete scene coverage.
Solution Approach 2:
The patent adds dimensional information to the traversal by incorporating instance IDs and hit point IDs into the hit point identification system. This dimensional enhancement allows the traversal algorithm to navigate the scene more efficiently by tracking not just spatial position but also instance identity, thereby reducing unnecessary traversal steps across overlapping geometries.
2Device complexity
If two-level acceleration structure is used for heavily-instanced scenes, then hierarchical organization is improved, but traversal complexity increases due to instance overlap
Solution Approach 1:
The patent applies preliminary action by pre-assigning unique instance IDs and hit point IDs to each instance and its constituent hit points before traversal begins. This pre-identification system is established in advance, allowing the traversal algorithm to efficiently navigate the two-level acceleration structure without getting confused by instance overlaps, thus maintaining high traversal efficiency.
Solution Approach 2:
The patent implements feedback mechanisms by using instance IDs and hit point IDs to track and distinguish hit points across different instances during traversal. This feedback system allows the algorithm to recognize when it has already processed a particular hit point in a different instance, preventing redundant intersections and improving overall traversal efficiency.
Data Source
AI summary
Apparatus and method for programmable ray tracing with hardware acceleration on a graphics processor. For example, one embodiment of a graphics processor comprises shader execution circuitry to execute a plurality of programmable ray tracing shaders. The shader execution circuitry includes a plurality of single instruction multiple data (SIMD) execution units. Sorting circuitry regroups data associated with one or more of the programmable ray tracing shaders to increase occupancy for SIMD operations performed by the SIMD execution units; and fixed-function intersection circuitry coupled to the shader execution circuitry detects intersections between rays and bounding volume hierarchies (BVHs) and/or objects contained therein and to provide results indicating the intersections to the sorting circuitry.