Integrating Specular Manifold Sampling in Cycles Renderer for Enhanced Specular Light Transport

Photorealistic rendering demands accurate simulation of complex light-transport phenomena, such as multi-bounce caustics generated by specular reflection and refraction. Standard path-tracing renderers, including Blender's Cycles, often struggle to efficiently capture these effects. While Cycles recently integrated Manifold Next Event Estimation (MNEE) to resolve specific refractive caustics, the technique remains limited to caustics that fall inside the caster's shadow, assumes smooth-shaded surfaces, and fails to capture refractive or reflective caustics outside shadow regions, or handle scenes with multiple concurrent specular paths. This thesis addresses these shortcomings by detailing the process of extending Cycles' framework with Specular Manifold Sampling (SMS), aiming to enhance its caustic rendering capabilities for refractive paths while documenting the significant challenges encountered, particularly with reflective interactions. The objective was achieved by enhancing Cycles' manifold-computation routines to support both reflective and refractive scenarios. New modules implement biased and unbiased SMS estimators. A stochastic initialization phase selects random surface points and microfacet normals to seed manifold exploration, enabling discovery of multiple light paths. Corresponding probability-estimation mechanisms were implemented for both the unbiased estimator (via repeated trials) and the biased estimator (via a fixed budget of unique solutions). These modules allow to skip parts of the existing direct-illumination sampling strategy. The implementation was evaluated on custom benchmark scenes featuring challenging refractive caustics. The results were assessed using metrics such as rendering time, samples per pixel (spp), root-mean-square error (RMSE), and Structural Similarity Index Measure (SSIM) against baseline Cycles with standard path tracing, and its original MNEE implementation. The primary outcome is a Cycles renderer with new capabilities for multi-bounce refractive caustics via SMS, alongside a documented account of the practical difficulties in porting such advanced research, highlighting areas where theoretical promise meets implementation complexities.