Graphics Reference
In-Depth Information
2
II
High Performance
Outdoor Light Scattering
Using Epipolar Sampling
Egor Yusov
2.1 Introduction
Light scattering effects in the atmosphere are crucial for creating realistic images
of outdoor scenes. These effects generate the blue color in a clear sky as well as
the spectrum of colors painting the horizon at sunset or sunrise. Light shafts,
or god rays, are also produced by the same physical phenomenon when some
sunlight is blocked by terrain features, such as mountains. Due to the complexity
and numerous computations required to accurately evaluate the airlight integral,
only rudimentary sky models are usually used in real-time rendering, which have
a number of limitations. For example, simple models cannot handle daytime
changes, restrict the camera to ground level, etc. Using screen-space imitation is
a common technique to render god rays.
This chapter presents a new high performance, physically based method for
computing outdoor light scattering effects while taking shadowing into account.
The method combines two key concepts: epipolar sampling, which significantly
reduces the number of samples for which expensive ray marching is performed,
and 1D minimum/maximum binary trees, which accelerate ray marching proce-
dure. The method is fully dynamic, and requires only a little pre-computation.
It renders scattering effects for all times of day and for all camera locations, from
ground views to outer space. The method is integrated with cascaded shadow
maps, which are commonly used to handle large outdoor environments.
