Ray Tracing Acceleration Structure Shader Execution
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Solution Overview
Problem
Ray tracing operations in graphics rendering suffer from divergence issues due to the execution of intersection and hit shaders during acceleration structure traversal, leading to inefficiencies in processing multiple rays and materials.
Innovation Solution
Instead of executing intersection and hit shaders during acceleration structure traversal, a shader program fully traverses the structure to record the closest intersection, and then launches waves to process continuation rays, reducing divergence by grouping materials and executing shaders only for the closest hit triangles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If intersection and hit shaders are executed during acceleration structure traversal, then material processing is performed, but processing efficiency deteriorates due to divergence in SIMD units
Solution Approach 1:
The patent segments the ray tracing process into two distinct phases: (1) acceleration structure traversal to identify closest hit triangles, and (2) shader execution for material processing. By separating the traversal phase from the shader execution phase, rays with the same closest hit triangle are grouped together and processed in batches, ensuring that SIMD units execute the same shaders for all active lanes, thereby eliminating divergence and improving processing efficiency.
2Manufacturing precision
If shaders are executed for each ray intersection during traversal, then material processing is accurate, but computational overhead increases
Solution Approach 1:
The patent performs preliminary acceleration structure traversal to identify and record the closest hit triangle for each ray before executing any shaders. This preliminary action groups rays by their closest hit triangle, allowing subsequent shader executions to be batched by material. This approach ensures material processing accuracy is maintained while significantly reducing computational overhead by avoiding repeated shader executions for rays hitting the same triangle.
3Measurement precision
If full acceleration structure traversal is performed for each ray, then closest intersection is accurately determined, but processing time increases
Solution Approach 1:
The patent merges multiple ray traversals by grouping rays that have the same closest hit triangle. Instead of performing full acceleration structure traversal independently for each ray, the system traverses the acceleration structure once per unique closest hit triangle and processes all rays hitting that triangle together. This merging approach maintains accurate closest intersection determination while reducing total processing time by eliminating redundant traversal operations.
Data Source
AI summary
Described herein is a technique for performing ray tracing. According to this technique, instead of executing intersection and/or any hit shaders during traversal of an acceleration structure to determine the closest hit for a ray, an acceleration structure is fully traversed in an invocation of a shader program, and the closest intersection with a triangle is recorded in a data structure associated with the material of the triangle. Later, a scheduler launches waves by grouping together multiple data items associated with the same material. The rays processed by that wave are processed with a continuation ray, rather than the full original ray. A continuation ray starts from the previous point of intersection and extends in the direction of the original ray. These steps help counter divergence that would occur if a single shader program that inlined the intersection and any hit shaders were executed.