Real-time woven fabric rendering using SGGX fitting

Realistic woven fabric rendering plays an important role in film production, video games, etc. The microflake model has recently been introduced for lightweight fabric rendering, which serves as the specular part of the woven fabric appearance. However, it cannot be used directly for real-time rendering due to the low sample count requirements for real-time rendering. The main challenge is a multi-scale representation which allows for efficient range query during rendering. To this end, we propose a multi-scale representation of the specular lobes of each yarn segment using SGGX fitting. More specifically, we precompute the normal distribution functions (NDFs) of the yarn segments with different query sizes and then use several SGGX functions to represent the NDFs. During rendering, we aggregate the contribution for each pixel by querying the fitted SGGXs of yarn segments covered by the pixel's footprint. We also propose a bounding box representation for the yarn segments, enabling a practical intersection with the pixel's footprint. As a result, our method is able to render several typical types of woven fabrics in only 1–2 ms at 1080p resolution using an RTX 3090 video card. Our method outperforms existing approaches and shows closer rendering results to reference results.