A survey of shadow algorithms
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paper_title: Algorithms for antialiased cast shadows

paper_content:

Abstract The ability to render the shadows cast by objects in a scene is of prime importance in augmenting the realism of sequences produced by image synthesis algorithms. From a theoretical standpoint, the problem does not present a great number of difficulties: It requires an integration in the process, of the viewpoint from the light source and the utilization of this information when calculating the lighting of the pixels. The purpose of this study is not to present a radically new approach, but to explore in depth the most common problem present in these images, the aliasing, or more generally speaking, the sampling problem. This work has implied a specific approach in the hidden surface determination, the introduction of a variation of the already used A-buffers or Z-buffers, as well as an extensive study of the filtering problem.
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paper_title: Spatial transformations for rapid scan-line surface shadowing

paper_content:

A novel approach to surface shadowing is presented that is based on a parallel solution to the hidden-surface (visibility) problem. The approach computes visibility along scan lines of a spatial transformation of the surface height data. The transformation aligns in scan lines all potentially occluding points on the surface, allowing rapid 1-D determination of whether a point can be seen by the light source. Using this approach, arbitrarily defined surfaces can be shadowed very much more quickly than by conventional methods; a 512*512 surface image can be shadowed in less than 30 s on a MicroVAX II. The method also provides an efficient preprocessor for realistic 3-D scene synthesis, allowing the marking of shadowed pixels to eliminate unnecessary diffuse and specular reflection computations. >
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paper_title: Rendering and animation of gaseous phenomena by combining fast volume and scanline A-buffer techniques

paper_content:

This paper describes a new technique that efficiently combines volume rendering and scanline a-buffer techniques. This technique is useful for combining all types of volume-rendered objects with scanline rendered objects and is especially useful for rendering scenes containing gaseous phenomena such as clouds, fog, and smoke. The rendering and animation of these phenomena has been a difficult problem in computer graphics.A new algorithm for realistically modeling and animating gaseous phenomena is presented, providing true three-dimensional volumes of gas. The gases are modeled using turbulent flow based solid texturing to define their geometry and are animated based on turbulent flow simulations. A low albedo illumination model is used that takes into consideration self-shadowing of the volumes.
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Title: A Survey of Shadow Algorithms

Section 1: Introduction
Description 1: Introduce the concept of shadows in computer graphics, outline the importance of shadow computation in image quality, and provide historical context and motivation for the survey of shadow algorithms.

Section 2: Complexity of Algorithms
Description 2: Discuss the complexity metrics used to compare shadow algorithms, including storage usage, preprocessing runtime complexity, and runtime complexity during actual rendering.

Section 3: Hard Shadow Generation
Description 3: Describe algorithms focused on generating hard shadows, which involve a binary decision process to determine whether points lie in the shadow of opaque objects.

Section 4: Fake Shadows
Description 4: Cover simpler, special-purpose algorithms that produce shadows under certain conditions or shortcuts, mainly used for real-time applications like video games.

Section 5: Shadow Volumes
Description 5: Detail the shadow volume technique, which involves creating polygonal shadow umbrae and updating shadow counts to determine visibility.

Section 6: Area Subdivision
Description 6: Explain the area subdivision algorithms that transform images into light source views and generate shadow information using polygon clipping techniques.

Section 7: Soft Shadow Generation
Description 7: Discuss algorithms for generating soft shadows, which include both umbra and penumbra regions, providing a higher level of visual quality.

Section 8: Intersection Culling Algorithms for Ray Tracing
Description 8: Explore various intersection culling algorithms designed to optimize ray tracing by limiting the set of candidate objects checked for intersections.

Section 9: Shadow Culling Algorithms for Ray Tracing
Description 9: Detail additional algorithms specific to culling shadow rays, further optimizing performance in shadow intersection tests.

Section 10: Frame Buffer Algorithm
Description 10: Describe the frame buffer approach for modeling higher dimensional light sources by generating shadow umbra polygons during preprocessing.

Section 11: Distributed Ray Tracing
Description 11: Cover the distributed ray tracing method, which involves shooting multiple shadow rays to capture soft shadow effects and other visual phenomena like motion blur.

Section 12: Cone Tracing
Description 12: Explain the concept of cone tracing, which extends ray tracing to area sampling, useful for generating soft shadows and antialiasing.

Section 13: Area Subdivision Approach
Description 13: Introduce a method involving the reverse application of polygon clippers to generate soft shadows from polygonal surfaces.

Section 14: Bidirectional Ray Tracing
Description 14: Present the bidirectional ray tracing technique for soft shadows resulting from inter-reflections using a uniform voxel structure.

Section 15: Radiosity
Description 15: Discuss the radiosity method for computing soft shadows by calculating diffuse inter-reflections between surfaces.

Section 16: Shadows from Transparent Objects
Description 16: Focus on the complexities of generating shadows from transparent objects, including effects like caustics and colored shadow regions.

Section 17: Shadows of Parametric and Implicit Surfaces
Description 17: Examine the challenges and methods for shadowing with parametric and implicit surfaces, including both numerical techniques and polygonization.

Section 18: Shadows on Texture-Mapped Surfaces
Description 18: Discuss shadow determination on surfaces with texture mapping, including bump mapping and transparency mapping.

Section 19: Self-Shadowing of Facets
Description 19: Explore the specific cases of self-shadowing in surfaces with complex local geometries, such as reflective facets.

Section 20: Shadows for Particle-Based Objects
Description 20: Describe shadow algorithms used for particle systems, which stochastically model complex objects like trees and clouds.

Section 21: Volume Densities
Description 21: Cover methods for simulating light interaction and shadow determination in volume densities like clouds or dusty surfaces.

Section 22: Participating Medium
Description 22: Discuss models for media that emit, scatter, and absorb light, extending volume density techniques to atmospheric and other volumetric effects.

Section 23: Conclusions
Description 23: Summarize the survey, highlighting the complexity and computational cost of shadow determination, and propose directions for future research.