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Titlereal-time realistic rendering of nature scenes with dynamic lighting
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Table of Contents
                            ABSTRACT
ACKNOWLEDGMENTS
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
CHAPTER
1 INTRODUCTION
CHAPTER
2 BACKGROUND
	2.1 Lighting
		2.1.1 Basic radiometric quantities
		2.1.2 Light transport equation
		2.1.3 Light sources
		2.1.4 Visibility function and ambient occlusion
		2.1.5 Global illumination
	2.2 Material properties
		2.2.1 BRDFs
		2.2.2 SBRDFs and BTFs
	2.3 Volume rendering
CHAPTER
3 PREVIOUS WORK
	3.1 Nature modeling and rendering
	3.2 Grass rendering
		3.2.1 Geometry-based rendering methods
		3.2.2 Image-based rendering methods
		3.2.3 Volume-based rendering methods
	3.3 Tree rendering
		3.3.1 Geometry-based modeling and rendering methods
		3.3.2 Image-based rendering methods
		3.3.3 Volume-based rendering methods
		3.3.4 Tree lighting
CHAPTER
4 RENDERING GRASS IN REAL-TIME WITH DYNAMIC LIGHTING
	4.1 Introduction
	4.2 Our grass rendering method
		4.2.1 Levels of detail
		4.2.2 Geometry-based rendering
		4.2.3 Volume rendering
		4.2.4 Management of non-uniform distribution of grass
		4.2.5 Seamless transition between levels of detail
		4.2.6 Shadows
		4.2.7 Management of the terrain
		4.2.8 Animation
	4.3 Implementation
		4.3.1 Global grass rendering algorithm
		4.3.2 Order-independent rendering of semi-transparent quadrilaterals
		4.3.3 A custom filter to create the mipmaps pyramid of a semi-transparent texture
	4.4 Results
CHAPTER
5 RENDERING TREES IN REAL-TIME WITH INDIRECT LIGHTING
	5.1 Introduction
	5.2 Overview
		5.2.1 Constructing the tree envelope
		5.2.2 Lighting environment
		5.2.3 Leaf materials
		5.2.4 Attenuation function
	5.3 Direct Lighting
		5.3.1 Light from the sky and the ground
		5.3.2 Directional Light Source
	5.4 Indirect Lighting
		5.4.1 Integration Scheme
		5.4.2 Evaluation of the sums
		5.4.3 Evaluation of the irradiance on neighbor leaves
	5.5 Shadows
		5.5.1 Shadows projected onto leaves by other leaves
		5.5.2 Shadows cast by trees
	5.6 Implementation
	5.7 Results
CHAPTER
6 CONCLUSION AND FUTURE WORK
APPENDIX
A SPHERICAL BARYCENTRIC INTERPOLATION OF THE GRASS BTF DATA
APPENDIX
B SIMPLIFICATION OF EQUATION 5.15
LIST OF REFERENCES
                        
Document Text Contents
Page 1

Real-Time Realistic Rendering of Nature Scenes with
Dynamic Lighting

by

Kévin Boulanger

M.S. INRIA, University of Rennes I, France, 2005

A dissertation submitted in partial fulflllment of the requirements
for the degree of Doctor of Philosophy

in the School of Electrical Engineering and Computer Science
in the College of Engineering and Computer Science

at the University of Central Florida
Orlando, Florida

Summer Term
2008

Major Professor:
Sumanta N. Pattanaik

Page 2

c© 2008 by Kévin Boulanger

Page 95

Figure 4.13: Values of ω, the size of the transition region between rendering methods, as
a function of the weight wvs(d). ω0 is a user-defined offset to avoid a division by 0 when
computing the opacity (Algorithm 1). We use ω0 = 0.05 in our implementation.

Firstly, the grass blades for which the density threshold (dth) is strictly greater than the

local density (ld) are eliminated. Among the remaining grass blades, the ones with dth less

than wvs(d).ld are rendered using slices and the others with geometry. wvs(d) ∈ [0, 1] so

we multiply it by the local density ld to get the transition point. We manage a window of

width ω around wvs(d).ld to get a smooth transition between the levels of detail. ω has to

be small when the local density is small, thus we multiply it by ld. We change the opacity

progressively in the range [(wvs(d)− ω).ld, (wvs(d) + ω).ld].

For a fixed local density ld, if the weight wvs(d) is close to 0 or to ld, the transition region

goes out of range, creating persistent semi-transparent grass blades. We take care of this

problem by decreasing ω depending on its proximity to the bounds 0 and ld. The function

for ω is shown in Figure 4.13.

The final algorithm to handle density for horizontal and vertical slices is presented in

Algorithm 1. These steps are executed at the beginning of the fragment shader, so it elimi-

nates many expensive computations (lighting in particular) when the fragments do not have

to be displayed. We consider whs(d) = wg(d) for d ≤ maxGeom.

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Algorithm 1: Density management for slices rendering

if ld < 0.01 then discard fragment;
if dth > ld then discard fragment;
ω = ωmax [ω0 + (1− ω0).(1− |2wvs(d)− 1|)];
opacity = clamp

‡(wvs(d) + ω).ld− dth
2ω.ld

, 0, 1
·
;

if opacity < 0.01 then discard fragment;

The algorithm for geometry rendering is the same except for the opacity. The following

expression presents this difference (we consider wvs(d) = 1− wg(d) for d ≤ maxGeom):

opacity = clamp
‡dth− (wvs(d)− ω).ld

2ω.ld
, 0, 1

·
(4.6)

4.2.6 Shadows

Shadows are an important part of realism in rendered scenes. If they are not present, the

rendered images look flat, with low contrast, and it is difficult to know the exact location of

3D objects relative to the others. However, rendering scenes with shadows involves expensive

computations, resulting in low frame rates. If we render exact shadows for each grass blade,

the computation cost becomes prohibitive. We need to perform fast approximations that

give visually pleasant dynamic shadows. There are three kinds of shadows: points on the

ground occluded from light by grass blades (Figure 4.14), points of grass blades occluded

from light by other blades (Figure 4.15) and self-shadowing of the blades. We do not manage

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