A Layered Method for Realistic Rendering of Towels and Carpets

We present a balanced method for realistic rendering of towels and carpets from a normal viewing distance. Since the yarn loops on the surface of a towel contribute more to the appearance of a towel than the underneath skeleton yarns do, we model yarn loops with more accurate geometry and lighting models. To show the randomness in the shape of a yarn loop, we control the shape of yarn loops by bilinear patches. To keep the continuity between the shapes of neighboring yarn loops, we determine the vertices of a bilinear patch by both the underneath towel stitch pattern and a turbulence function. We also present a reasonably simplified method to ray trace the a yarn loop volume. In our ray-tracing method, only one intersection point needs to be calculated for each incident ray. Both our lighting model and geometry model can also be applied to other layered objects (e.g. fur and grasses).