Sheared Bounding Boxes for Faster Ray-Box Intersection Tests
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ray tracing technologies face inefficiencies due to the use of axis-aligned bounding boxes (AABBs) that fail to tightly bound non-axis-aligned geometry, leading to increased false positive intersections and reduced traversal performance, especially in real-time hardware-accelerated implementations.
Innovation Solution
Employing sheared axis-aligned bounding boxes (SAABBs) that approximate oriented bounding boxes by applying a localized shear transform before performing ray-box tests, allowing tighter fitting bounding volumes and reducing false positives without incurring significant computational overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If axis-aligned bounding boxes (AABBs) are used for ray tracing, then storage and computation efficiency are maintained, but false positive intersections increase when bounding non-axis-aligned geometry
Solution Approach 1:
The patent transforms the coordinate system by applying a shear transform to the ray rather than transforming the bounding box. This parameter change in the ray's coordinate representation allows the ray to be accurately tested against axis-aligned bounding boxes in the transformed space, eliminating false positives while maintaining AABB efficiency.
Solution Approach 2:
The patent introduces an intermediate coordinate transformation step as a mediator between the ray and the bounding box test. By transforming the ray into a coordinate system where the bounding boxes are axis-aligned, the intermediary transform enables accurate intersection testing without requiring oriented bounding boxes.
2Reliability
If oriented bounding boxes (OBBs) are used to tightly bound non-axis-aligned geometry, then false positive intersections are reduced, but computational overhead increases significantly
Solution Approach 1:
Instead of transforming the bounding boxes to be oriented (the conventional approach), the patent inverts the problem by transforming the ray into a coordinate system where the bounding boxes become axis-aligned. This inversion maintains the simplicity of AABBs while achieving the accuracy of OBBs.
Solution Approach 2:
The patent changes the parameters of the ray (its coordinate representation) rather than changing the bounding box orientation. By applying a shear transform to the ray's direction and origin, the ray is expressed in a transformed coordinate system where standard AABB tests remain computationally simple.
3Reliability
If sheared axis-aligned bounding boxes (SAABBs) are used with localized shear transforms, then tighter fitting bounding volumes are achieved, but computational overhead increases
Solution Approach 1:
The patent makes the ray tracing system self-service by transforming the ray itself to adapt to the bounding box geometry. The ray transformation is integrated into the existing ray tracing pipeline, allowing the system to achieve tighter bounding volumes using the same computational resources already allocated for ray processing.
Data Source
AI summary
To improve the efficiency of bounding volumes in a hardware based ray tracer, we employ a sheared axis-aligned bounding box to approximate an oriented bounding box typically defined by rotations. To achieve this, the bounding volume hierarchy builder shears an axis-aligned box to fit tightly around its enclosed oriented geometry in top level or bottom level space, then computes the inverse shear transform. The bounds are still stored as axis-aligned boxes in memory, now defined in the new sheared coordinate system, along with the derived parameters to transform a ray into the sheared coordinate system before testing intersection with the boxes. The ray-bounding volume intersection test is performed as usual, just in the new sheared coordinate system. Additional efficiencies are gained by constraining the number of shear dimensions, constraining the shear transform coefficients to a quantized list, sharing a shear transform across a collection of bounds, performing a shear transform only for ray-bounds testing and not for ray-geometry intersection testing, and adding a specialized shear transform calculator/accelerator to the hardware.