Shadow Volumes in Complex Scenes

Christian Steiner
Shadow Volumes in Complex Scenes
[thesis]

Information

Abstract

Over the last 10 years, significant progress has been made in the field of computer graphics, especially in real-time rendering. Most noteworthy, the use of dedicated graphics accelerator hardware has found its way from the professional to the consumer market, and their ever increasing power has allowed for rendering almost photorealistic virtual environments while still maintaining interactive framerates. Despite this rapid development, a significant element of computer graphics has been neglected for a long time. Shadows do not only provide more realistic-looking scenes, but also aid the viewer in perceiving spatial relationships. However, due to the additional computational requirements, it has been impossible for graphics accelerators to render shadows and keep framerates high enough to maintain the feeling of immersion for a long time. Although there are several approaches to realize shadows, dynamic environments with a multitude of light sources and complex objects still make high demands on the hardware. In this thesis, a technique is presented to improve the performance of shadow volumes in complex scenes that consist of a large number of individual objects. Several optimization techniques have already been proposed that target applications where the rasterization of the shadow volume polygons is the main bottleneck. However, these optimizations usually assume that the number of individual objects in the scene is rather small compared to the number of geometric primitives (triangles). In such scenes, calculations can be accelerated by using low-polygon approximations of the actual geometry. Most of these existing optimization techniques relieve the graphics hardware at the cost of increased CPU load. If the CPU is already at peak load, these techniques do not achieve any performance gain, but rather worsen the bottleneck in the CPU stage, resulting in an even lower performance. This thesis first presents an overview of current state-of-the-art shadowing techniques that are based on standard shadow volumes. Then, we will try to adapt parts of these techniques to work in complex scenes. Specifically, we will improve visibility determination for shadow volume culling in GPU-demanding scenes with lots of individual objects, as well as present a method for the fast creation of segmented (clamped) shadow volumes that tightly fit the shadow-receiving geometry using vertex programs (shaders).

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BibTeX

@mastersthesis{STEINER-2006-SVC,
  title =      "Shadow Volumes in Complex Scenes",
  author =     "Christian Steiner",
  year =       "2006",
  abstract =   "Over the last 10 years, significant progress has been made
               in the field of computer graphics, especially in real-time
               rendering. Most noteworthy, the use of dedicated graphics
               accelerator hardware has found its way from the professional
               to the consumer market, and their ever increasing power has
               allowed for rendering almost photorealistic virtual
               environments while still maintaining interactive framerates.
               Despite this rapid development, a significant element of
               computer graphics has been neglected for a long time.
               Shadows do not only provide more realistic-looking scenes,
               but also aid the viewer in perceiving spatial relationships.
               However, due to the additional computational requirements,
               it has been impossible for graphics accelerators to render
               shadows and keep framerates high enough to maintain the
               feeling of immersion for a long time. Although there are
               several approaches to realize shadows, dynamic environments
               with a multitude of light sources and complex objects still
               make high demands on the hardware. In this thesis, a
               technique is presented to improve the performance of shadow
               volumes in complex scenes that consist of a large number of
               individual objects. Several optimization techniques have
               already been proposed that target applications where the
               rasterization of the shadow volume polygons is the main
               bottleneck. However, these optimizations usually assume that
               the number of individual objects in the scene is rather
               small compared to the number of geometric primitives
               (triangles). In such scenes, calculations can be accelerated
               by using low-polygon approximations of the actual geometry.
               Most of these existing optimization techniques relieve the
               graphics hardware at the cost of increased CPU load. If the
               CPU is already at peak load, these techniques do not achieve
               any performance gain, but rather worsen the bottleneck in
               the CPU stage, resulting in an even lower performance. This
               thesis first presents an overview of current
               state-of-the-art shadowing techniques that are based on
               standard shadow volumes. Then, we will try to adapt parts of
               these techniques to work in complex scenes. Specifically, we
               will improve visibility determination for shadow volume
               culling in GPU-demanding scenes with lots of individual
               objects, as well as present a method for the fast creation
               of segmented (clamped) shadow volumes that tightly fit the
               shadow-receiving geometry using vertex programs (shaders).",
  month =      may,
  address =    "Favoritenstrasse 9-11/E193-02, A-1040 Vienna, Austria",
  school =     "Institute of Computer Graphics and Algorithms, Vienna
               University of Technology ",
  keywords =   "shadow volumes, coherent hierarchical culling, cc shadow
               volumes, real-time rendering",
  URL =        "https://www.cg.tuwien.ac.at/research/publications/2006/STEINER-2006-SVC/",
}