使用球冠采样可见GGX法线
Sampling Visible GGX Normals with Spherical Caps
AI总结：
本研究提出一种基于半球面镜反射形成球冠的洞见，通过入射方向与球冠采样方向的半向量采样可见GGX法线的新方法，实现比Heitz方法更简单且有系统性速度提升的效果。
摘要：
对可见GGX法线分布进行重要性采样需要对半球的可见法线进行采样。在本研究中，我们提出了一种采样此类可见法线的新方法。我们的方法基于这样的洞见：半球面镜会在呈球冠形状的立体角内均匀反射平行光线。该球冠与半球面镜具有相同的顶点，其孔径由该顶点的取向与入射光线方向形成的角度决定。基于这一洞见，我们将GGX可见法线作为给定入射方向与从其关联球冠中抽取的方向之间的半向量进行采样。我们最终的实现甚至比Heitz的实现更简单，并且在我们的基准测试中实现了最高达系统性的速度提升。
英文摘要：
Importance sampling the distribution of visible GGX normals requires sampling those of a hemisphere. In this work, we introduce a novel method for sampling such visible normals. Our method builds upon the insight that a hemispherical mirror reflects parallel light rays uniformly within a solid angle shaped as a spherical cap. This spherical cap has the same apex as the hemispherical mirror, and its aperture given by the angle formed by the orientation of that apex and the direction of incident light rays. Based on this insight, we sample GGX visible normals as halfway vectors between a given incident direction and directions drawn from its associated spherical cap. Our resulting implementation is even simpler than that of Heitz and leads to up to systematic speed-ups in our benchmarks.
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