Soft Shadowing via Pre-computed Visibility Logs
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Solution Overview
Problem
Existing techniques for generating soft shadows in real-time are computationally complex and inefficient, especially when dealing with dynamic scenes containing multiple moving objects, as they require extensive numerical integration and spherical harmonic operations.
Innovation Solution
The technique pre-computes visibility logs of blockers and accumulates them in log space, allowing for real-time exponentiation to obtain the product visibility vector, which is then combined with light intensity and surface reflectance to determine shading, reducing computational costs and enabling efficient handling of multiple blockers and dynamic geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If numerical integration over many light directions is used to generate soft shadows, then shadow accuracy is improved, but rendering time increases excessively
Solution Approach 1:
The patent pre-computes visibility logs for all blockers in the scene before rendering. These visibility logs capture the shadowing effects of blockers at sampled points in volumetric space around each blocker. By performing this complex integration work beforehand, the actual real-time rendering only needs to accumulate pre-computed logs and exponentiate them, reducing rendering time while maintaining shadow accuracy.
2Measurement precision
If spherical harmonic operations are used to compute soft shadows with multiple blockers, then shadow quality is improved, but computational complexity increases
Solution Approach 1:
The patent pre-computes spherical harmonic visibility logs for all blockers before runtime rendering. Each blocker's visibility function is expanded in spherical harmonics and stored as logs. During real-time rendering, the system accumulates these pre-computed logs and exponentiates them to obtain the product visibility vector, avoiding the need to perform spherical harmonic products at runtime and significantly reducing computational complexity.
3Productivity
If visibility logs are accumulated and exponentiated in real-time, then computation speed is improved, but mathematical operation complexity increases
Solution Approach 1:
The patent transforms the visibility computation problem by working in log space instead of direct visibility space. By accumulating logs of visibility functions and then exponentiating the sum, the system converts a complex product operation into a simpler sum operation followed by a single exponentiation. This parameter transformation maintains computational speed while managing mathematical complexity.
Data Source
AI summary
The present soft shadowing technique pre-computes visibility of blockers using a log of a spherical harmonic visibility function. These logs can then be accumulated and exponentiated in real-time to yield the product visibility vector over all the blockers. The product visibility vector is combined with the light intensity and surface reflectance to determine shading at a receiver point in a computer-generated scene.