Sub-Primitive Presence Compression for Low-Latency Ray Tracing
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Solution Overview
Problem
Existing ray tracing systems experience latency and increased computational load due to frequent execution of shader programs to determine the presence of punch through primitives during intersection testing, which is not optimally addressed by existing methods like sub-triangle opacity masks that significantly increase data usage.
Innovation Solution
A method and system for compressing and decompressing sub-primitive presence indications using vector quantization techniques, leveraging the non-random distribution of presence states to reduce data size and minimize shader program execution, implemented through a compression unit and decompression unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sub-triangle opacity masks are used to determine primitive presence during intersection testing, then the accuracy of presence determination is improved, but the data size increases significantly
Solution Approach 1:
The primitive is divided into multiple sub-primitives (e.g., sub-triangles), and presence indications are generated for each sub-primitive. This segmentation allows for more precise presence determination while enabling efficient compression by grouping sub-primitives into sub-blocks with shared presence states.
Solution Approach 2:
Multiple sub-primitives are grouped into sub-blocks, and presence indications for sub-primitives within the same sub-block are merged into a single shared presence indication. This reduces the total number of presence indications from one per sub-primitive to one per sub-block, significantly compressing the data size.
2Measurement precision
If shader programs are executed frequently to determine primitive presence, then the accuracy of intersection testing is improved, but the latency and power consumption increase
Solution Approach 1:
Presence indications for sub-primitives are pre-calculated and stored in compressed form before intersection testing. During runtime, the decompressed presence indications are used to quickly determine primitive presence without executing shader programs, eliminating the latency and power consumption associated with frequent shader executions.
Solution Approach 2:
Compressed presence indication data acts as an intermediary between the geometry data and the intersection testing logic. Instead of executing shader programs to determine primitive presence, the system uses the pre-computed and decompressed presence indications as a mediator to quickly determine whether a primitive is present at a given sample position.
3Loss of information
If more presence indication data is stored for each primitive, then the completeness of presence information is improved, but the memory usage increases
Solution Approach 1:
The compression scheme applies different levels of detail to different regions of the primitive based on local requirements. Sub-blocks are grouped into regions, and presence indications are shared within regions, allowing the system to maintain complete presence information where needed while compressing data in regions where primitives share similar presence characteristics.
Solution Approach 2:
The presence indication data structure uses a composite approach, combining multiple levels of organization: individual sub-primitive presence states, sub-block groupings with shared presence indications, and regional groupings with shared candidates. This multi-level composite structure enables efficient compression while preserving the completeness of presence information.
Data Source
AI summary
A method and a decompression unit are provided for decompressing compressed data to determine one or more sub-primitive presence indications for use in a rendering system. A block of compressed data for a block of sub-primitive presence indications is received. The block of sub-primitive presence indications comprises a plurality of sub-blocks of sub-primitive presence indications. The block of compressed data comprises, for each of the sub-blocks in the block of sub-primitive presence indications, an index to indicate one of a plurality of candidates for combinations of presence indications. An index is read from the block of compressed data for one of the sub-blocks in the block of sub-primitive presence indications. Candidate data is obtained representing at least a portion of the candidate indicated by the read index. The obtained candidate data is used to determine one or more of the presence indications in the sub-block.