real-time shadow casting using fake soft shadow...
TRANSCRIPT
REAL-TIME SHADOW CASTING USING FAKE SOFT SHADOW VOLUME
WITH STENCIL BUFFER
LEE KONG WENG
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Science (Computer Science)
Faculty of Computer Science and Information System
Universiti Teknologi Malaysia
MARCH 2006
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To my mum
beloved Jess, family and friends.
Thanks for all the encouragement and loves …
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ACKNOWLEDGEMENT
My first thanks goes to Associate Professor Daut Daman, my supervisor for
encouragement, guidance, critics and motivation. Without his help this thesis would
not be have been the same as presented here, if not almost impossible. Besides that, I
would to thank him for making me to write and published paper, which in the end
helps me a lot in this research thesis.
The second thanks go to the department of Computer Graphics and
Multimedia, UTM staff and lecturer for their contribution towards this research. I’m
also indebted to Universiti Teknologi Malaysia (UTM) and Ministry Of Science,
Technology and Innovation (MOSTI) for funding my Master’s research. Other
thanks including to those researchers, academicians and practitioners who made
available their research work on the internet that help a lot in my research.
The final thanks go to my beloved Jessica for the encouragement, motivation,
critics, arguments and making my heart warm. The next thanks goes to my mum and
family for the support and understanding. Thanks to Baldeve, Saandi, Yus and my
other lab mate for the discussions which are related or non-related to my research.
Not to forget the next lab boys and girls for providing food and entertainment such as
network game during the time when my brain seems to be offline (if your supervisor
happen to be my evaluator then you all in big trouble), then there are group of course
mate who always providing relaxation with badminton games and water recreation at
Kota Tinggi. Thanks and may God bless all of you.
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ABSTRACT
Shadows are essential to realistic and visually appealing images. The important elements in shadows are the accuracy and the dynamics of hard shadows, which provide scene information and spatial cue. Soft shadows on the other hand provide the realism. The research goal is to create an accurate and real-time dynamic fake soft shadow using stencil shadow volume algorithm. The performance of the algorithm must maintain the quality at acceptable level, as it is the main criteria. In this research, a point light source is used and the occluder is an opaque object. Culling and particle system are excluded, and light source are not allowed to get close to the occluder. The methodology consists of two steps; first is to create the hard shadow using shadow volume with stencil buffer, and second is to add in the soft shadow effects. The first step involves silhouette determination of the occluder, construction of the shadow volume by extruding the silhouette to a very large value, and rendering the shadow volume with depth-pass technique in order to determine which objects are to be shadowed. The second step is to retrieve the original geometry of the hard shadows, and to produce samples of hard shadows with a sequentially enlarged and softened colour. All these samples are finally averaged and blended together to produce the soft shadow effects. The algorithm is implemented using C++ and OpenGL where the occluders are ranging from simple to complex objects. Comparison using proposed algorithm with an established algorithm revealed that the proposed algorithm is two to five times faster. Results from various tests reveal that the proposed algorithm not only achieves better frame per second performance but also maintains the quality of soft shadows. Therefore, the importance of soft shadows cannot be neglected as it increases realism in computer-generated scenes.
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ABSTRAK
Bayang-bayang penting kepada imej yang realistik dan menarik. Elemen utama dalam bayang-bayang adalah ketepatan dan kedinamikan bayang-bayang kasar kerana ia memberikan maklumat dan kue spatial. Bayang-bayang lembut pula memberikan kesan realistik. Matlamat penyelidikan ini adalah untuk menghasilkan bayang-bayang lembut palsu dinamik yang tepat dan masa nyata menggunakan algoritma isipadu bayang-bayang stensil. Pencapaian algoritma ini mestilah mengekalkan kualiti pada tahap yang boleh diterima kerana ia adalah kriteria utama. Dalam kajian ini sumber cahaya titik digunakan dan penghadang adalah objek yang tidak lutsinar. Sistem partikel dan penakaian dikecualikan dan sumber cahaya tidak dibenarkan menghampiri penghadang. Metodologi terbahagi kepada dua peringkat; pertama ialah untuk menghasilkan bayang-bayang kasar menggunakan isipadu bayang-bayang dengan penimbal stensil, dan kedua ialah untuk menambah kesan bayang-bayang lembut. Peringkat pertama melibatkan penentuan bayang-bayang bagi penghadang, pembinaan isipadu bayang-bayang dengan memanjangkan bayang-bayang ke satu nilai yang besar, dan menghasilkan isipadu bayang-bayang dengan teknik lulus-kedalaman untuk menentukan objek yang perlu menjana bayang-bayang. Peringkat kedua ialah mendapatkan geometri asal bayang-bayang kasar, dan menghasilkan sampel bayangan kasar dengan pembesaran berjujukan dan warna yang dilembutkan. Semua sampel ini akhirnya dipuratakan dan digabungkan untuk menghasilkan kesan bayang-bayang lembut. Algoritma ini dilaksanakan menggunakan C++ dan OpenGL di mana julat penghadang ialah dari objek yang mudah sehingga kompleks. Perbandingan antara algoritma cadangan dengan algoritma yang telah terbukti menunjukkan bahawa algoritma cadangan ialah dua hingga lima kali lebih laju. Keputusan dari beberapa ujian menunjukkan bahawa algoritma cadangan bukan sahaja mencapai kelajuan kerangka per saat yang lebih baik tetapi juga mengekalkan kualiti bayang-bayang lembut. Oleh itu, kepentingan bayang-bayang lembut tidak boleh dinafikan kerana ia menambah realistik dalam pemandangan janaan komputer.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
THESIS STATUS DECLARATION
SUPERVISOR’S DECLARATION
COOPERATION DECLARATION
TITLE i
ORIGINALITY AND EXCLUSIVENESS DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xii
LIST OF FIGURES xiii
LIST OF ABBREVIATIONS xviii
LIST OF APPENDICES xix
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Research Background 2
1.3 Current Issues 4
1.4 Problem Statement 6
1.5 Research Goal 8
1.6 Research Objectives 8
1.7 Research Scopes 8
1.8 Research Contributions 9
1.9 Organisation of Thesis 11
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2 LITERATURE REVIEW 12
2.1 Introduction 12
2.2 Hard Shadow vs. Soft Shadow 14
2.3 Real-Time Methods 15
2.3.1 Planar/Projection Shadows 15
2.3.1.1 Blinn’s Method 16
2.3.1.2 Nguyen’s Method 16
2.3.1.3 Plateau Soft Shadows 17
2.3.2 Shadow Map 18
2.3.2.1 Traditional Shadow Maps 19
2.3.2.2 Percentage Closer Filtering 20
2.3.2.3 Deep Shadow Maps 21
2.3.2.4 Adaptive Shadow Maps 23
2.3.2.5 Perspective Shadow Maps 24
2.3.2.6 Heckbert and Herf Soft Shadows 25
2.3.2.7 Efficient Soft Shadows by ATI 26
2.3.3 Shadow Volume 28
2.3.3.1 Traditional Shadow Volume -
Projected Shadow Polygon 28
2.3.3.2 Stencil Shadow Volume 29
2.3.3.3 Hybrid Method – Shadow Volume
Reconstruction 31
2.3.3.4 Stencil Shadow Volume With
Depth Pass 32
2.3.3.5 Stencil Shadow Volume With
Depth Fail/Carmack Reverse 32
2.3.3.6 Approximate Soft Shadows On
Arbitrary Surfaces Using Penumbra
Wedges 34
2.3.3.7 Soft Shadow Using Fast Coverage
Calculation for Spherical Light
Sources 35
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2.4 Non Real-Time Methods 36
2.4.1 Ray Tracing 36
2.4.1.1 Distributed Ray Tracing 37
2.4.1.2 Bi-directional Ray Tracing 38
2.4.2 Radiosity 38
2.4.2.1 Hemi-Cube 39
2.4.2.2 Shadow Polygons 39
2.5 Comparison Of Real-time Shadow Techniques 40
3 RESEARCH METHODOLOGY 43
3.1 Introduction 43
3.2 Creation Of Fake Soft Shadow Volume With
Stencil Buffer 45
3.2.1 Step 1: Creating Hard Shadow -
Shadow Volume 45
3.2.1.1 Silhouette Determination 47
3.2.1.2 Shadow Volume Construction 50
3.2.1.3 Rendering Shadow Volume Using
Depth-Pass Technique 54
3.2.2 Step 2: Adding Fake Soft Shadow 56
3.2.2.1 Getting The Geometry Of Original
Hard Shadows 57
3.2.2.2 Generating The Samples Of Hard
Shadows 57
3.2.2.3 Blending/Averaging The Samples
Of Hard Shadows 58
3.3 Algorithm Optimisation And Compromises For
Real-Time Performance 60
3.3.1 Quality And Performance 60
3.3.2 Pre-computation 61
3.3.3 Point Light Source And Finite Extrusion 61
3.3.4 Penumbra/Soft Shadow Always At The
Outer Shadow 62
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4 DESIGN AND IMPLEMENTATION 63
4.1 Introduction 63
4.2 Comparison of Software and Hardware Specification 64
4.3 Phase 1: Constructing The Scene 65
4.3.1 Model Data 66
4.3.2 Environment 70
4.4 Phase 2: Creating Shadow Volume – Hard Volume 70
4.4.1 Constructing Data Structure 70
4.4.2 Silhouette Determination 72
4.4.3 Shadow Volume Construction 74
4.4.4 Rendering Shadow Volume Using Depth-
Pass Technique 74
4.5 Phase 3: Adding Fake Soft Shadows 75
5 TEST RESULTS, ANALYSIS AND DISCUSSION 78
5.1 Introduction 78
5.2 Accuracy of Resemblance Test 82
5.3 Realism Test 89
5.3.1 Parameter Test 89
5.3.2 Comparison Against Other Algorithm 91
5.4 Real-Time Test 92
5.4.1 Speed Testing On Different Soft Shadows
Algorithms On Different Systems 92
5.4.2 Speed Testing Comparison On Different
Soft Shadows Algorithms With Different
Numbers Of Polygon 95
5.4.3 Speed Testing Comparison On Different
Numbers Of Polygons Using Research
Prototype 100
5.5 Relation Between Numbers Of Model Polygons,
Hard Shadow Polygons And Soft Shadow Polygons 103
5.6 Summary 111
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6 CONCLUSIONS AND FUTURE WORKS 112
6.1 Conclusions 112
6.2 Future Works 115
REFERENCES 117
Appendices A1 - E2 122 - 133
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LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Comparisons on real-time shadow techniques 41
4.1 Specifications of systems used for
implementation and testing 64
4.2 Specifications of graphic hardware used for
implementation and testing 65
5.1 Comparison of soft shadow generated 91
5.2 Model or shadow caster selected 96
5.3 Model and the polygon counts 100
5.4 Model’s and shadow attributes 103
5.5 Test with length = 3 and various gap values 105
5.6 Linear equation generated from graph of hard
shadow polygon count vs. soft shadow polygon
count with length = 3 110
5.7 Relation between length, gap and slope value, m 110
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Penumbra and umbra generation 12
2.2 Self-shadow and cast shadow 13
2.3 Categories of shadow techniques 13
2.4 Pixel transition for hard shadow and soft shadow 14
2.5 Example Of Nguyen's technique 17
2.6 Adding soft shadows at the edge of hard shadow 18
2.7 Ordinary texture map filtering 20
2.8 Percentage closer filtering 21
2.9 A scene rendered using deep shadow maps 22
2.10 Without self-shadowing and with self-shadowing 23
2.11 Number of samples required 26
2.12 Shadow with fewer samples and with more
samples 26
2.13 Soft shadow of vase and soft shadow textures 27
2.14 Silhouette calculation 29
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2.15 Original stencil shadow volume 30
2.16 When eye/camera is in shadow 33
2.17 The hard shadows split the penumbra 35
2.18 Form factors 39
2.19 Shadow technique evolution 42
3.1 Research framework 44
3.2 Silhouette edges 45
3.3 Shadow volume clipping with view volume 46
3.4 Indexed triangle mesh 48
3.5 Consistent winding for two triangle faces sharing
the same edge 49
3.6 Failure of finite shadow volume in shadowing
other objects 51
3.7 Extrusion option 51
3.8 The edge for casting shadow volume 52
3.9 Extruding to “infinity” by producing two new
additional vertices 53
3.10 Depth-pass 55
3.11 Work flow for adding soft shadows 57
3.12 Samples of new hard shadows generated 58
3.13 Stacking of the samples and original shadow
volumes 59
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3.14 Comparison of original shadow volume and new
soft shadow volume 59
3.15 Length and gap factors 60
4.1 Research phases 63
4.2 Steps to generate file data for model 66
4.3 MilkShape 3D 67
4.4 3D Studio ASCII and data of vertices and faces of
triangular Polygons 68
4.5 The output file data with normals calculated 69
4.6 Occluder/model data structure 71
4.7 First pass and second pass 75
5.1 Soft shadow effects on a cross 78
5.2 Soft shadow effects on a cube 79
5.3 Soft shadow effects on a sphere 79
5.4 Soft shadow effects on Object 1 80
5.5 Soft shadow effects on Object 2 80
5.6 Soft shadow effects on a pot 81
5.7 Soft shadow effects on MD2 Knight 81
5.8 Quake III developed by id Software in 1999 83
5.9 Medal of Honours by Electronic Arts release on
2002 84
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5.10 Frozen Throne by Blizzard Entertainment released
in 2003 85
5.11 Realistic and accurate shadows in action, Medal
of Honour:Pacific Assault released by Electronic
Arts in 2004 85
5.12 Shadow of a cube and a sphere 86
5.13 Shadow of Object 1 87
5.14 Shadow of a cross and Object 2 87
5.15 Shadow of a pot 88
5.16 Shadow of MD2 Knight 88
5.17 Test results using a cube with different lengths
and gaps factor 90
5.18 FPS vs. model polygon counts for three different
systems using Fake Soft Shadow Volume with
Stencil Buffer 93
5.19 FPS vs. model polygon counts for three different
systems using Approximate Soft Shadows on
Arbitrary Surfaces Using Penumbra Wedges
algorithm 95
5.20 Different systems and soft shadows algorithms vs.
FPS for a cylinder model with 216 polygons 96
5.21 Different systems and soft shadows algorithms vs.
FPS for a knight model with 634 polygons 97
5.22 Different systems and soft shadows algorithms vs.
FPS for a lizard model with 1842 polygons 99
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5.23 Shadow polygon counts vs. FPS for hard shadow
implementation 101
5.24 Shadow polygon counts vs. FPS for hard and soft
shadow implementation 102
5.25 Model polygon counts vs. hard shadow polygon
counts vs. soft shadow polygon counts for
length = 3 and gap = 1.0 106
5.26 Model polygon counts vs. hard shadow polygon
counts 107
5.27 Model polygon counts vs. soft shadow polygon
counts 108
5.28 Hard shadow polygon counts vs. soft shadow
polygon counts with length = 3 and gap =1.0 109
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LIST OF ABBREVIATIONS
.asc - ASCII file format
.txt - Text file format
2D - Two dimensional
3D - Three dimensional
CPU - Central Processing Unit
FPS - Frame per seconds
GB - Gigabyte
GHz - Giga Hertz
GPU - Graphic Processing Unit
MHz - Mega Hertz
PC - Personal Computer
RAM - Random Access Memory
RAMDAC - Random Access Memory Digital to Analog Converter
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LIST OF APPENDICES
APPENDIX TITLE PAGE
A1 Soft shadows effects on Cube 122
A2 Soft shadows effects on Sphere 123
A3 Soft shadows effects on Object 1 124
A4 Soft shadows effects on Object 2 125
A5 Soft shadows effects on Pot 126
A6 Soft shadows effects on MD2 Knight 127
B Test results using Object 2 with different length
and gap 128
C Test results using different model, systems and
algorithms 129
D1 Model polygon counts vs. hard shadow polygon
counts vs. soft shadow polygon counts for
length = 3 and gap = 0.7 130
D2 Model polygon counts vs. hard shadow polygon
counts vs. soft shadow polygon counts for
length = 3 and gap = 0.5 131
E1 Hard shadow polygon counts vs. soft shadow
polygon counts with length = 3 and gap =0.7 132
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E2 Hard shadow polygon counts vs. soft shadow
Polygon counts with length = 3 and gap =0.5 133
CHAPTER 1
INTRODUCTION
1.1 Introduction
Computer graphics have become one of the most important entities in
advertisements, virtual environment applications, simulations and games. Today’s
users have become smarter and more sensitive with highly sophisticated
requirements towards what they view on computer screen, displays or console. This
has been a rocket development since ten years back, when users were still indulged
in the green screen DOS environment that is nearly wiped out by today’s
technologies.
Programmers nowadays write computer graphics applications and tools in
high-level language such as C and C++ to run on hardware with gigantic memory,
speedy access to secondary storage, powerful CPUs, high resolution displays and
hardware graphics acceleration. This is however still far from today’s user’s demand
and expectation, which have outstripped the increase in PC performance, forcing
programmers to enhance graphics content and features while struggling to maintain
high performance.
Computer graphics applications and tools such as virtual environments,
simulations and games have utilised very sophisticated and complex algorithms to
make them realistic and life-like. Components such as lighting, shading, texture
mapping, shadows and others are the main elements in making a scene look realistic.
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Hence, this research is aimed at developing an algorithm for generating soft shadows
in real-time. Shadows, which play an important role in making a scene look realistic,
are essential in games, virtual environment applications and simulation because they
represent information for decision-making. The more realistic a shadow is the more
informative it is for an analysis.
Shadows are essential to realistic and visually appealing images, but they are
difficult to compute in most display environment especially in real-time games
(Haller et al., 2003). In computer games, shadows give the gamers the feel of
dramatic and spooky effects. A game without the shadow effects is considered to
lack realism. The scene tends to look flat and it is difficult to determine the size and
spatial relation of the objects in the scene.
Besides being the main ingredient in adding realism to a scene, shadows also
provide important spatial cues or information (Gibson et al., 2003). This enables the
viewer to determine whether an object is located on the plane or some distance away.
Just as with lighting, the increasing level of realism will decrease rendering
performance.
1.2 Research Background
The early work on shadows brings us back to 1977 when Frank Crow first
published his paper on Shadow Algorithm’s for Computer Graphics (Crow, 1977).
His method explicitly clips shadow geometry to the view frustum, generating perfect
caps where the volume crosses a clipping plane. Heidmann (1991) suggested the use
of stencil buffer to implement Crow's original algorithm that gave the algorithm the
name “stencil shadow volume” by which it is best known today. Stencil shadows
belong to the group of volumetric shadow algorithms, as the shadowed volume in the
scene is explicit in the algorithm.
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In year 2000, Carmack suggested a slightly different approach which entails
that the view rays are traced from infinity towards the eye. The tracing ends when
encountering the pixel on the geometry that is closest to the eye, which is discussed
in (Carmack, 2000). This reversal of the view rays' direction has given the algorithm
the name Carmacks reverse.
Lengyel (2002) created a hybrid algorithm that uses faster z-pass rendering
when the view port is not shadowed and reverts to robust z-fail rendering when the
view port is shadowed. Several new improvement methods based upon shadow
volume are suggested. Assarson et al. (2002, 2003) describe how to create soft
shadows using penumbra wedges rendered from shadow volume. Fauerby Kjaer
(2003) used a technique for highly efficient coverage calculation for spherical light
sources. This technique can avoid clipping operations in the pixel shader and let the
texture sampler do the clipping for free. However, this technique has a setback being
limited to spherical light sources.
Shadow mapping by Williams (1978) is an alternative, image-based method
for shadow determination. It offers an advantage over the shadow volume technique
for its performance is not directly dependent on the complexity of the shadowing
object. It is essentially a technique involving the transformation of distances from
one viewpoint, that of the viewer to distances from another viewpoint, that of the
light source. Unlike shadow volume, shadow maps have the ability to shadow any
object that can be rendered.
A lot of variants of shadow maps were studied and developed because of the
problems in shadow maps such as aliasing and quantisation. The Deep Shadow
proposed by Lokovic and Veach from Pixar Animation Studios, is a new and more
evolved shadowing technique suited especially for producing fast and high-quality
shadows of self-shadowing primitives such as hair, fur and smoke (Lokovic and
Veach, 2000). Adaptive Shadow Maps by Fernando et al. (2001) which are an
extension to the traditional shadow mapping technique, remove aliasing problems by
resolving pixel size mismatches between the eye and light source views. An
approach to adapt shadow map resolution to the current view is discussed in
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(Stamminger and Drettakis, 2002). By using a non-uniform parameterisation, a
single perspective shadow map can be generated, providing high resolution for near
objects and decreased resolution for a viewer who moves away from the viewpoint.
Another interesting technique for shadow generation that has recently been
demonstrated by McCool is a hybrid of the shadow volume technique and the
shadow map technique. This technique, Shadow Volume Reconstruction by McCool
(2000), is based on the observation that once a shadow map has been generated, the
information in the shadow map (i.e. the depth, or z information for the scene as
observed from the light source) defines a volume.
Last but not least is the planar/projection method which, although being
inaccurate, is top in its class in terms of performance. An easy-to-implement type of
shadow can be created using projection transforms. An object is simply projected
onto a plane, and then rendered as a separate primitive. Computing the shadow
involves applying an orthographic or perspective projection matrix to the model view
transform, then rendering the projected object in the desired shadow colour. Blinn
(1988) admits to having first attempted an approach to solve the problem in an
unintuitive (but slightly quicker) way. He also presented his revised methodical
approach (Blinn, 1996) and showed problems associated with it.
1.3 Current Issues
Currently most real-time shadow algorithms have been limited to hard
shadows. Hard shadows are the result of light sources being modelled as a single
point with no area and can be recognised by a very sharp transition from light into
shadow. If light sources are modelled with an actual shape of an area or volume, soft
shadows can be produced. Soft shadows can be recognised by their inclusion of a
penumbra region: an area that is neither fully lit nor fully in shadow.
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The visual quality of soft shadows compared to that of hard shadows is very
high. It is thus highly desirable to be able to apply real-time soft shadows to
computer games. Unfortunately, the computations required for soft shadows are
much more complex than those required for hard shadows (Chan and Durand, 2003).
Currently, no released game has utilised true, real-time and dynamic soft shadows.
Real world shadows are usually soft with a smooth transition from full light
to full shadow. This effect is due to the indirect illumination and the volume light
source. Light sources within a volume of soft shadows are points where a part of the
light is visible. This is called the penumbra region. The areas where the geometry is
in full shadow with no visible light are called the umbra region.
Currently, there are a few techniques that generate soft shadows. These
techniques include Plateaus, Heckbert and Herf, technique by ATI and penumbra
wedges in shadow volume. The latest technique is by Kasper and Carsten using fast
coverage calculation for spherical light sources. However, unlike those hard shadow
algorithms, all these soft shadow algorithms have never been implemented in any
game engines or any real-time applications.
The next issue concerns hardware development. Nowadays, graphic cards
are so significantly fast in rendering graphics. The two biggest leading companies,
NVIDIA Corp and ATI Technologies Inc have produced graphics cards that give
end-users graphics performance that once could only be run on supercomputers.
Besides giving end-users high graphics performance, they also produce innovative
tools for developing better graphics-related applications that maximise the usage of
hardware. NVIDIA Corp in close collaboration with Microsoft Corporation has
come up with Cg, a high-level C-like graphics programming language. The Cg
environment consists of two components: the Cg Toolkit including the NVIDIA Cg
Compiler Beta 1.0 optimised for DirectX® and OpenGL®; and the NVIDIA Cg
Browser, a prototyping/visualisation environment with a large library of Cg shaders.
Meanwhile ATI has developed Radeon SDK 2.0 to rival NVIDIA Cg. Radeon SDK
2.0 also takes the advantage of ATI® products using Microsoft DirectX®. In the
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next section, more will be discuss on the improvement in hardware particularly by
these two mammoth companies.
Another change to the hardware development is the use of two-sided stencil
testing. This new feature in recent GPU’s allows the application programmer to set
up and use different stencil states and operations for back facing and front facing
triangles respectively. This reduces the CPU load of issuing render calls to the
driver, reduces the amount of vertices that have to be transformed through a vertex
shader, and reduces the amount of mesh data that has to be sent to the graphics card
over the AGP bus. This development has led to significant gain in performance.
These features however are only available in current graphic cards. Besides
providing two-sided stencil, NVIDIA’s high-end graphic cards also come with
UltraShadow Technology for next generation games like Doom III from id Software
in providing real-time cinematic effects of shadow. With the addition of
programmable vertex shader functionality, another significant improvement to the
algorithm is made possible. The calculation of the shadow mesh can be moved from
the CPU to the GPU (McGuire and Hughes, 2004), which of course lifts a burden
from the CPU but, more importantly, it also means that the shadow mesh data can be
sent to the GPU one shot instead of every frame as was previously necessary.
1.4 Problem Statement
Real-time shadows remain a huge challenge to the developers of computer
graphics applications and games. Fifteen frames per second are considered a
standard for real-time animation, which gives mere 0.067 second for a developer to
construct and render the whole scene (Govindaraju et al., 2003). Most of the real-
time shadows techniques reviewed here concentrate on giving realistic and accurate
shadows. However, with limited time given, many methods have been developed to
improve rendering speed at the expense of reduced quality.
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Simple, inaccurate shadows (dark ellipse or rectangle below an object) have
been used over the past. This is because some representation of shadows is better
than none at all. However, this is not the solution for today’s applications that
demand more accurate, realistic and dynamic shadows. In 1991, Heidmann
implemented accurate dynamic hard shadows that demonstrated the possibility of
implementing shadow volume algorithm with stencil buffer. At that time, it only
worked on fairly expensive high-end systems. Accurate dynamic shadows became
commonly used around 1999 due to graphics hardware improvement and the
generalisation of the algorithm presented by Carmack (2000).
However, there were later problems related to the realism of the shadows.
The real-world shadows consist of soft shadows, the transitions of which from dark
region to no shadow region are smooth. Though soft shadows are important in
adding realism to a computer generated scenes but in general a fake soft shadow is
enough for the current needs. This is because it does not matter whether shadows are
soft or hard as the shadows still represent the same spatial cue and information.
High quality shadows come with a price of reduction in performance. So, to
what extent of reduction in quality that can be tolerable and acceptable without
compromising performance? The reduction of performance should not slow down
the other functions such as rendering, lighting and others. A huge number of point
lights are required to avoid obvious sampling artifacts, though this normally is done
using graphics hardware.
Many of the algorithms developed are too computationally intensive for real-
time purpose. It is assumed that the target system is a PC or similar devices
equipped with the common hardware acceleration for graphics. A common method
to enhance the performance of an algorithm is to utilise graphics hardware. Triangle
rendering can be implemented efficiently using hardware function. With the current
states of development in graphics hardware, there is a hope that lot of shadow
rendering algorithms can be transferred to GPU's rather than CPU’s in the near
future.
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1.5 Research Goal
The ultimate goal of this research is to develop an algorithm for generating
dynamic and realistic shadows using the shadow volume technique. The fake soft
shadows generated which could achieve a real-time rate, can eventually be used in
games, simulations and virtual environments.
1.6 Research Objectives
[1] To develop a shadow technique that creates an accurate shadow.
[2] To develop algorithm that are able to generate fake soft shadows which are
capable of increasing realism in a scene.
[3] To develop a real-time shadow technique for scene rendering while
maintaining high quality of shadows and frame-rate.
1.7 Research Scopes
The scopes of research are described as follows:
[1] The light source used in this research is a point light source, which does not
have the effect of an ambient light spreading out.
[2] The generation of shadow excludes objects that use particle systems such as
hair, grass, smoke and fog. Such objects shadow each other, sometimes
itself, and the quantity of the polygons involved are enormous. With this, it is
too complex and involves a lot of computation, making real-time
implementation impossible.
[3] This research involves occluders that are opaque objects. Light penetrable
objects such as semi-transparent and glasses are excluded. Such object will
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permit some light to pass through them, which may alter the colour of
shadows.
[4] The scenes consist of one light source at a time. Rendering more than one
light source will require additional complex calculation and increase CPU
usage; this in return will slow down the rendering process.
[5] Culling is not implemented in this research as in real game engine. Only the
area of shadow that is viewed by eye/camera is rendered. Shadows are
independent of the eye/camera position. But if culling is implemented it will
reduce the number of polygons rendered.
[6] The situation where the light source gets very close to the occluder is also not
included in this research. This is because shadow volumes eventually
collapse into an increasingly marginal volume when the light gets extremely
close.
[7] The improvement will focus on algorithm efficiency, not on hardware related
enhancement. However, basic standard hardware acceleration function that is
available on most major graphics acceleration will be utilised in
implementing the algorithm.
[8] This research will only consider the outer penumbra with the assumption that
the shadow will always have umbra.
1.8 Research Contributions
The main contribution of this research is the development of a shadow
technique that enables the creation of reasonably accurate shadows resembling the
shadow caster geometry. The algorithm use in this research is the well known
shadow volume, the algorithm generates umbra. The umbra is then use to produce
the penumbra. Hence, the soft shadow effects produce is a high quality dynamic soft
shadow using existing software library and current graphics hardware.
10
The research algorithm is suitable for applications where the need to achieve
both real-time performance and accurate soft shadow are essential. The research
algorithm sacrifice the quality of the soft shadow effects to the extent of tolerate able
to achieve real-time performance. With the enhancement of graphics hardware in the
future, this algorithm will be able to cater for far more complex scenes.
The algorithm will be suitable for applications that emphasise on speed,
realism and accuracy. Stated in the following are the applications that will benefit
from this algorithm:
• Film Industry
Special effects in movie require such an algorithm to help create realistic
shadows for capturing and sustaining viewers’ attention. It adds realism in
cartoons and science-fiction movies.
• Game
With the enhancement of scenes, especially those created by computers, the
gamers will feel as though they are immersed in the game itself. This will give a
feeling of pure satisfaction and real-life experience.
• Simulation/Virtual Environment
The shadow effects provide the users of simulation applications a realistic and
real-life experience.
• Geographic Information System (GIS) Application
VIRTUAL GIS that has become an important tool for GIS scientists to make
realistic and real-life applications possible with the shadow effects.
11
1.9 Organisation of Thesis
This thesis consists of six chapters as described:
• Chapter 1 briefly states the introduction of the research and the research
background. The current issues are discussed and problem statements defined.
The goal, objectives and the scopes of the research were defined. In addition, the
contributions made by this research are also stated.
• Chapter 2 discusses in details the various categories of techniques available in
generating shadows. The pros and cons of the techniques were reviewed,
discussed and compared in the literature.
• Chapter 3 explains the research methodologies that are applied in this research.
This chapter shows all the steps taken to develop the research algorithm in detail.
• Chapter 4 addresses the implementation of the algorithm developed. This
includes the implementation of the methodology mentioned in Chapter 3 and the
required considerations for the implementation to succeed.
• Chapter 5 reveals and discusses the results from the implemented prototype and
its testing.
• Chapter 6 wraps up the research with concluding remarks and states the benefits
gained from the research. Also stated are suggestions about future improvement
work that can be further explored.
116
The recent developments of graphics hardware bring hopes to graphics
applications developers and researchers. This is because most of the future
development of soft shadow volume algorithm depends on graphics hardware
features and speed. As graphics hardware become more affordable and powerful,
there is no reason for developers and researchers not to further develop soft shadow
volume algorithm. Future developers or researchers must take advantage of the
graphics hardware to develop realistic and real-time soft shadow for graphics
applications and games.
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