Combining spherical harmonics and point lights for real-time photorealistic rendering

Photorealistic rendering with all frequency lights and materials and their visibility in real time is a difficult problem. The environment lights and complex materials can be approximated with spherical harmonics defined in spherical Fourier domain. Then, low frequency components of complex environment lights and materials are projected on just a few bases of spherical harmonics, which makes real-time rendering possible in low dimensional space. However, high frequency components, such as small bright light and glossy reflection, are filtered out during the spherical harmonics projection. In the other hand, point lights are efficient to represent high frequency lights, while they are inefficient for low frequency lights, such as smooth area lights. Combining spherical harmonics and point lights approaches, we can render a scene in real time, preserving both of low and high frequency effects. To include visibility information in real time system, we adopt screen space directional occlusion approach.