GPU Pro 5

2. High Performance Outdoor Light Scattering Using Epipolar Sampling 111

Epipolar line

Epipolar sample

Light ray

View ray

Figure 2.5. Epipolar geometry: camera rays casted through the samples on an epipolar

line and light rays lie in the same plane.

Taking shadow map samples along this line results in a one-dimensional height

map, which is the same for all camera rays in the slice. To perform a visibility

test V (P ) in equation (2.2) and Listing 2.1, we essentially need to check if the

current position on the view ray is under this height map or above it (Figure 2.6).

It is clear that if there is a long consecutive lit or shadowed section on the ray