Fast Geometric Sampling for Phong-Like Reflection

Importance sampling is a critical technique for reducing the variance of Monte Carlo samples. However, the classical importance sampling based on the Bidirectional Reflectance Distribution Function (BRDF) is often complex and challenging to implement. In this work, we present a simple yet efficient sampling method inspired by Phong’s reflectance model. Our method generates samples of rays using geometric vector operations, replacing the need for BRDF. We explain our implementation of this method on WebGL and demonstrate how we obtain per-pixel random numbers in GLSL. We also conduct experiments to compare our method’s speed and patterns to the Phong distribution. The results show that our sampling process can simulate reflections similar to Phong, but is about three times faster than traditional Phong or other BRDF importance sampling methods. Our sampling method is applicable to both real-time and offline rendering, making it a useful tool for computer graphics applications.