Physically Based Area Lights - GPU Pro: Advanced Rendering Techniques - page 67

1

II

Physically Based Area Lights
Michal Drobot

1.1 Overview

This chapter presents the physically based area lighting system used in Killzone:
Shadow Fall , developed by Guerrilla Games for Playstation 4 (see Figure 1.1).
We present a novel, real-time, analytical model for area lights, capable of
supporting multiple light shapes. Each shape can be represented by simple 3D
or 2D functions on a plane. Discussed applications include the following light
shapes: sphere, disk, and rectangle.
The model supports diffuse and specular lighting. BRDF (bidirectional re-
flectance distribution function) implementation in Killzone: Shadow Fall ren-
dering engine explicitly splits the material reflectance model from the lighting
model itself. This allows a separation between different surface simulation algo-
rithms and light types, which supply the former with required light quantities.
To achieve this, we use the importance sampling principle to approximate non-
finite or computationally expensive integrals in the material reflectance part of
the BRDF. This chapter focuses only on the derivation of the proposed framework
and actual light modeling part.
All lights in the rendering engine are physically based area lights, described
by radiometric quantities such as light intensity in lumens, dimensions in meters,
world orientation, and light shape type. We introduce a specialized description of
surface roughness that is shared or adapted to match various surface reflectance
models. The light model uses light description and surface roughness, at the
point being shaded, to deliver light quantity arriving at the point—split between
the light model and the surface reflectance model.
In addition we discuss integration of the proposed model into deferred ren-
derer and how it was used as a principle for environmental probe generation and
dynamic analytical texture-based area lights.