Tangent-Plane Parameterization for Coarse Pixel Shading Continuity
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Solution Overview
Problem
Coarse Pixel Shading (CPS) in rasterization-based graphics pipelines faces issues with shading continuity, leading to artifacts such as sudden texture level of detail changes and temporal flickering, especially with smaller triangles and coarse shading rates, due to mismatching texture derivatives and extrapolation artifacts.
Innovation Solution
Pre-processing the mesh to create a unique tangent-plane parameterization of smooth vertex attributes for each vertex, ensuring consistent derivatives across triangles, and implementing alternative sampling patterns and higher-order filtering to avoid extrapolation and improve texture filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If coarse pixel shading is used to reduce shader evaluations and improve power efficiency, then productivity and energy efficiency are improved, but shading continuity deteriorates causing artifacts such as sudden texture level of detail changes and temporal flickering
Solution Approach 1:
The patent applies preliminary action by pre-processing the mesh to create a unique tangent-plane parameterization of smooth vertex attributes for each vertex before rasterization. This ensures that when coarse pixel shading is applied, the attribute extrapolation starts from a smooth, continuous foundation, preventing the shading continuity artifacts that would otherwise occur with standard per-triangle shading approaches
Solution Approach 2:
The patent changes the parameterization approach from standard per-triangle linear interpolation to tangent-plane parameterization with smooth vertex attributes. This parameter transformation ensures that attributes vary smoothly across triangle boundaries even when shader evaluations are decoupled from visibility sampling, resolving the continuity issues while maintaining coarse shading benefits
2Device complexity
If standard per-triangle shader attribute derivatives are used, then device complexity is kept simple, but manufacturing precision of texture derivatives deteriorates causing mismatching derivatives across triangle boundaries
Solution Approach 1:
The patent performs preliminary computation of smooth vertex attributes and tangent-plane parameterization before rasterization. This pre-processing step ensures that when primitives are rasterized and attributes are extrapolated, the derivatives are already optimized for continuity across triangle boundaries, achieving high precision without complicating the core shading pipeline
Solution Approach 2:
The patent introduces smooth vertex attributes as an intermediary between the mesh geometry and the rasterization process. These intermediate attributes act as a bridge that carries smooth variation information through the rasterization stage, allowing continuous texture derivatives to be maintained even when using simplified per-primitive shading approaches
3Measurement precision
If centroid interpolation is used to address attribute extrapolation issues, then shading accuracy is improved, but object-generated harmful factors worsen due to temporal flickering and revealed internal triangle edges
Solution Approach 1:
The patent changes the interpolation parameterization from centroid-based to tangent-plane parameterization with smooth vertex attributes. This parameter transformation fundamentally alters how attributes are computed and extrapolated, achieving both high accuracy and temporal stability without the artifacts associated with centroid interpolation
Data Source
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AI summary
An apparatus and method for performing coarse pixel shading (CPS). For example, one embodiment of a method comprises: A method for coarse pixel shading (CPS) comprising: pre-processing a graphics mesh by creating a tangent-plane parameterization of desired vertex attributes for each vertex of the mesh; and performing rasterization of the mesh in a rasterization stage of a graphics pipeline using the tangent-plane parameterization.