A Survey of Real-time Soft Shadows Algorithms
---
paper_title: A survey of shadow algorithms

paper_content:

The various types of shadows are characterized. Most existing shadow algorithms are described, and their complexities, advantages, and shortcomings are discussed. Hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives are considered. For each type, shadow algorithms within various rendering techniques are examined. The aim is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs and to help identify the areas that need more research and point to possible solutions. >
---
paper_title: The Perception of Cast Shadows

paper_content:

Abstract When an object casts its shadow on a background surface, the shadow can be informative about the shape of the object, the shape of the background surface and the spatial arrangement of the object relative to the background. Among all these roles, we found that cast shadows were perceptually most relevant for the recovery of spatial arrangement, especially when the shadow is in motion. This finding is intriguing when one considers the ambiguities in the possible ways that shadow motion can be interpreted. We reasoned that the visual system must use a priori constraints to disambiguate the cast shadow motion. One of these constraints is that the light source is stationary. Though simple, the stationary-light-source constraint supports rich, reliable inferences about the qualitative motions of objects in three dimensions.
---
paper_title: Moving Cast Shadows and the Perception of Relative Depth

paper_content:

We describe a number of visual illusions of motion in depth in which the motion of an object's cast shadow determines the perceived 3D motion of the object. The illusory percepts are phenomenally very strong. We analyze the information which cast shadow motion provides for the inference of 3D object motion and experimentally measure human observers' use of this information. The experimental results show that cast shadow information overrides a number of other strong perceptual constraints, including viewers' assumptions of constant object size and a general viewpoint. Moreover, they support the hypothesis that the human visual system incorporates a stationary light source constraint in the perceptual processing of shadow motion. The system imposes the constraint even when image information suggests a moving light source.
---
paper_title: A fast shadow algorithm for area light sources using backprojection

paper_content:

The fast identification of shadow regions due to area light sources is necessary for realistic rendering and for discontinuity meshing for global illumination. A new shadow-determination algorithm is presented that uses a data structure, called a backprojection , to represent the visible portion of a light source from any point in the scene. A complete discontinuity meshing algorithm is described for polyhedral scenes and area light sources, which includes an important class of light/geometry interactions that have not been implemented before. A fast incremental algorithm for computing backprojections is also described. The use of spatial subdivision, and heuristics based on computed statistics of typical scenes, results in efficient mesh and backprojection computation. Results of the implementation show that the use of the backprojection and discontinuity meshing permits accelerated high-quality rendering of shadows using both ray-casting and polygon-rendering with interpolants.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: A fast shadow algorithm for area light sources using backprojection

paper_content:

The fast identification of shadow regions due to area light sources is necessary for realistic rendering and for discontinuity meshing for global illumination. A new shadow-determination algorithm is presented that uses a data structure, called a backprojection , to represent the visible portion of a light source from any point in the scene. A complete discontinuity meshing algorithm is described for polyhedral scenes and area light sources, which includes an important class of light/geometry interactions that have not been implemented before. A fast incremental algorithm for computing backprojections is also described. The use of spatial subdivision, and heuristics based on computed statistics of typical scenes, results in efficient mesh and backprojection computation. Results of the implementation show that the use of the backprojection and discontinuity meshing permits accelerated high-quality rendering of shadows using both ray-casting and polygon-rendering with interpolants.
---
paper_title: Interactive High-Quality Soft Shadows in Scenes with Moving Objects

paper_content:

Interactive rendering of soft shadows (or penumbra) in scenes with moving objects is a challenging problem. High quality walkthrough rendering of static scenes with penumbra can be achieved using pre-calculated discontinuity meshes, which provide a triangulation well adapted to penumbral boundaries, and backprojections which provide exact illumination computation at vertices very efficiently. However, recomputation of the complete mesh and backprojection structures at each frame is prohibitively expensive in environments with changing geometry. This recomputation would in any case be wasteful: only a limited part of these structures actually needs to be recalculated. We present a novel algorithm which uses spatial coherence of movement as well as the rich visibility information existing in the discontinuity mesh to avoid unnecessary recomputation after object motion. In particular we isolate all modifications required for the update of the discontinuity mesh by using an augmented spatial subdivision structure and we restrict intersections of discontinuity surfaces with the scene. In addition, we develop an algorithm which identifies visibility changes by exploiting information contained in the planar discontinuity mesh of each scene polygon, obviating the need for many expensive searches in 3D space. A full implementation of the algorithm is presented, which allows interactive updates of high-quality soft shadows for scenes of moderate complexity. The algorithm can also be directly applied to global illumination.
---
paper_title: Rendering antialiased shadows with depth maps

paper_content:

We present a solution to the aliasing problem for shadow algorithms that use depth maps. The solution is based on a new filtering technique called percentage closer filtering. In addition to antialiasing, the improved algorithm provides soft shadow boundaries that resemble penumbrae. We describe the new algorithm in detail, demonstrate the effects of its parameters, and analyze its performance.
---
paper_title: Casting curved shadows on curved surfaces

paper_content:

Shadowing has historically been used to increase the intelligibility of scenes in electron microscopy and aerial survey. Various methods have been published for the determination of shadows in computer synthesized scenes. The display of shadows may make the shape and relative position of objects in such scenes more comprehensible; it is a technique lending vividness and realism to computer animation. To date, algorithms for the determination of shadows have been restricted to scenes constructed of planar polygons. A simple algorithm is described which utilizes Z-buffer visible surface computation to display shadows cast by objects modelled of smooth surface patches. The method can be applied to all environments, in fact, for which visible surfaces can be computed. The cost of determining the shadows associated with each light source is roughly twice the cost of rendering the scene without shadows, plus a fixed transformation overhead which depends on the image resolution. No extra entities are added to the scene description in the shadowing process. This comprehensive algorithm, which permits curved shadows to be cast on curved surfaces, is contrasted with a less costly method for casting the shadows of the environment on a single ground plane. In order to attain good results, the discrete nature of the visible-surface computations must be treated with care. The effects of dither, interpolation, and geometric quantization at different stages of the shadowing algorithm are examined. The special problems posed by self-shadowing surfaces are described.
---
paper_title: Deep shadow maps

paper_content:

We introduce deep shadow maps , a technique that produces fast, high-quality shadows for primitives such as hair, fur, and smoke. Unlike traditional shadow maps, which store a single depth at each pixel, deep shadow maps store a representation of the fractional visibility through a pixel at all possible depths. Deep shadow maps have several advantages. First, they are prefiltered, which allows faster shadow lookups and much smaller memory footprints than regular shadow maps of similar quality. Second, they support shadows from partially transparent surfaces and volumetric objects such as fog. Third, they handle important cases of motion blur at no extra cost. The algorithm is simple to implement and can be added easily to existing renderers as an alternative to ordinary shadow maps.
---
paper_title: Perspective shadow maps

paper_content:

Shadow maps are probably the most widely used means for the generation of shadows, despite their well known aliasing problems. In this paper we introduce perspective shadow maps, which are generated in normalized device coordinate space, i.e., after perspective transformation. This results in important reduction of shadow map aliasing with almost no overhead. We correctly treat light source transformations and show how to include all objects which cast shadows in the transformed space. Perspective shadow maps can directly replace standard shadow maps for interactive hardware accelerated rendering as well as in high-quality, offline renderers.
---
paper_title: Adaptive shadow maps

paper_content:

Shadow maps provide a fast and convenient method of identifying shadows in scenes but can introduce aliasing. This paper introduces the Adaptive Shadow Map (ASM) as a solution to this problem. An ASM removes aliasing by resolving pixel size mismatches between the eye view and the light source view. It achieves this goal by storing the light source view (i.e., the shadow map for the light source) as a hierarchical grid structure as opposed to the conventional flat structure. As pixels are transformed from the eye view to the light source view, the ASM is refined to create higher-resolution pieces of the shadow map when needed. This is done by evaluating the contributions of shadow map pixels to the overall image quality. The improvement process is view-driven, progressive, and confined to a user-specifiable memory footprint. We show that ASMs enable dramatic improvements in shadow quality while maintaining interactive rates.
---
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.
---
paper_title: Shadow algorithms for computer graphics

paper_content:

Shadows are advocated for improved comprehension and enhanced realism in computer-synthesized images. A classification of shadow algorithms delineates three approaches: shadow computation during scanout; division of object surfaces into shadowed and unshadowed areas prior to removal of hidden surfaces; and inclusion of shadow volumes in the object data. The classes are related to existing shadow algorithms and implementations within each class are sketched. A brief comparison of the three approaches suggests that the last approach has the most appealing characteristics.
---
paper_title: Improving Shadows and Reflections via the Stencil Buffer

paper_content:

For too many game developers, the above statement sums up their approach to 3D hardwareacceleration. A game programmer might turn on some fog and maybe throw in some transparency, but that’s often the limit. The question is whether that is enough anymore for a game to stand out visually from the crowd. Now everybody’s using 3D hardware-acceleration, and everybody’s slinging textured polygons around, and, frankly, as a result, most 3D games look more or less the same.
---
paper_title: Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering

paper_content:

Twenty-five years ago, Crow published the shadow volume approach for determining shadowed regions in a scene. A decade ago, Heidmann described a hardware-accelerated stencil bufferbased shadow volume algorithm. However, hardware-accelerated stenciled shadow volume techniques have not been widely adopted by 3D games and applications due in large part to the lack of robustness of described techniques. This situation persists despite widely available hardware support. Specifically what has been lacking is a technique that robustly handles various "hard" situations created by near or far plane clipping of shadow volumes. We describe a robust, artifact-free technique for hardwareaccelerated rendering of stenciled shadow volumes. Assuming existing hardware, we resolve the issues otherwise caused by shadow volume near and far plane clipping through a combination of (1) placing the conventional far clip plane “at infinity”, (2) rasterization with infinite shadow volume polygons via homogeneous coordinates, and (3) adopting a zfail stencil-testing scheme. Depth clamping, a new rasterization feature provided by NVIDIA's GeForce3 & GeForce4 Ti GPUs, preserves existing depth precision by not requiring the far plane to be placed at infinity. We also propose two-sided stencil testing to improve the efficiency of rendering stenciled shadow volumes.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: Shadow Volumes Revisited

paper_content:

We present a method to utilize the Shadow Volume Algorithm by Crow and Williams without using a stencil buffer. We show that the shadow mask can be generated in the alpha channel or even in the screen buffer, if a hardware-accelerated stencil buffer is not available. In comparison to the original stencil buffer method, a small speed up can be achieved, if the shadow mask is computed in the alpha buffer. The method using the screen buffer requires the scene to be rendered a second time after the shadow mask has been computed. Both methods are less restrictive with respect to hardware requirements, since we use only standard color blending and depth testing. In general, rasterization bandwidth is the main bottle neck when generating the shadow mask at high screen resolutions. In order to overcome this bottle neck we propose a way to compute the shadow mask at a resolution that is lower than the resolution of the screen buffer. Then the shadow mask is applied to the scene by utilizing texture mapping. The latter method might be reasonable especially in interactive entertainment, where rendering speed is traded in favour of image quality.
---
paper_title: Practical and Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering

paper_content:

Twenty-five years ago, Crow published the shadow volume approach for determining shadowed regions in a scene. A decade ago, Heidmann described a hardware-accelerated stencil bufferbased shadow volume algorithm. However, hardware-accelerated stenciled shadow volume techniques have not been widely adopted by 3D games and applications due in large part to the lack of robustness of described techniques. This situation persists despite widely available hardware support. Specifically what has been lacking is a technique that robustly handles various "hard" situations created by near or far plane clipping of shadow volumes. We describe a robust, artifact-free technique for hardwareaccelerated rendering of stenciled shadow volumes. Assuming existing hardware, we resolve the issues otherwise caused by shadow volume near and far plane clipping through a combination of (1) placing the conventional far clip plane “at infinity”, (2) rasterization with infinite shadow volume polygons via homogeneous coordinates, and (3) adopting a zfail stencil-testing scheme. Depth clamping, a new rasterization feature provided by NVIDIA's GeForce3 & GeForce4 Ti GPUs, preserves existing depth precision by not requiring the far plane to be placed at infinity. We also propose two-sided stencil testing to improve the efficiency of rendering stenciled shadow volumes.
---
paper_title: Soft shadow maps for area light by area approximation

paper_content:

Shadow mapping has been a popular way of generating shadows in real-time applications, but it is still incapable of generating realistic real time soft shadows for area light. There is an algorithm for generating soft shadows for linear light with few samples, but the algorithm is not suitable for area light. The author presents a modified method to the shadow mapping algorithm for linear light. The new method can produce convincing soft shadows for area light in real time applications.
---
paper_title: Single Sample Soft Shadows

paper_content:

A simple extension to ray tracing is presented that creates visually plausible “soft” shadows with little extra computation. Although these soft shadows are approximate, they are robust and have penumbra widths that behave in a believable way, including accurate placement of singularities where penumbra width is zero. The method has continuous behavior in space and time, so it is appropriate for both static and dynamic image generation.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: Distributed rendering of interactive soft shadows

paper_content:

Recently several distributed rendering systems have been developed that exploit a cluster of commodity computers by connecting host graphics cards over a fast network to form a compositing pipeline. This paper introduces an algorithm for one such system to parallelize contributions from arbitrary numbers of OpenGL lights, for example to compute approximate soft shadows by sampling area light sources. The algorithm renders multiple shadow maps across nodes of the cluster by factoring the OpenGL lighting equation into illumination and material properties. Additional parallelism is achieved by utilizing multiple texture units within each graphics card. Illumination by L point sources can be rendered by (L/K) + 1 nodes where K is the number of texture units on each graphics card. For walkthrough applications each node requires a single rendering pass, while for scenes with dynamic lights or geometry K+ 1 passes are needed per node. We present results using fragment shaders on nVidia Ge- Force4 Ti4600 and ATI Radeon 8500 graphics cards, and a cycle-accurate simulation of the compositing operators. These results show interactive frame rates for walkthroughs and dynamic models rendering shadows with 32 light sources on 9 nodes of a Sepia-2a distributed rendering cluster.
---
paper_title: Rendering Fake Soft Shadows with Smoothies

paper_content:

We present a new method for real-time rendering of shadows in dynamic scenes. Our approach builds on the shadow map algorithm by attaching geometric primitives that we call "smoothies" to the objects' silhouettes. The smoothies give rise to fake shadows that appear qualitatively like soft shadows, without the cost of densely sampling an area light source. The soft shadow edges hide objectionable aliasing artifacts that are noticeable with ordinary shadow maps. Our algorithm computes shadows efficiently in image space and maps well to programmable graphics hardware. We present results from several example scenes rendered in real-time.
---
paper_title: Real-Time Soft Shadows Using a Single Light Sample

paper_content:

We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by today’s graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering.
---
paper_title: Single Sample Soft Shadows Using Depth Maps

paper_content:

In this paper we propose a new method for rendering soft shadows at interactive frame rates. Although the algorithm only uses information obtained from a single light source sample, it is capable of producing subjectively realistic penumbra regions. We do not claim that the proposed method is physically correct but rather that it is aesthetically correct. Since the algorithm operates on sampled representations of the scene, the shadow computation does not directly depend on the scene complexity. Having only a single depth and object ID map representing the pixels seen by the light source, we can approximate penumbrae by searching the neighborhood of pixels warped from the camera view for relevant blocker information. We explain the basic technique in detail, showing how simple observations can yield satisfying results. We also address sampling issues relevant to the quality of the computed shadows, as well as speed-up techniques that are able to bring the performance up to interactive frame rates.
---
paper_title: Soft shadow maps for area light by area approximation

paper_content:

Shadow mapping has been a popular way of generating shadows in real-time applications, but it is still incapable of generating realistic real time soft shadows for area light. There is an algorithm for generating soft shadows for linear light with few samples, but the algorithm is not suitable for area light. The author presents a modified method to the shadow mapping algorithm for linear light. The new method can produce convincing soft shadows for area light in real time applications.
---
paper_title: Simulating Soft Shadows with Graphics Hardware

paper_content:

Abstract : This paper describes all algorithm for simulating soft shadows at interactive rates using graphics hardware. On current graphics workstations, the technique can calculate the soft shadows cast by moving, complex objects onto multiple planar surfaces in about a second. In a static, diffuse scene, these high quality shadows can then be displayed at 30 Hz, independent of the number and size of the light sources. For a diffuse scene, the method precomputes a radiance texture that captures the shadows and other brightness variations on each polygon. The texture for each polygon is computed by creating registered projections of the scene onto the polygon from multiple sample points on each light source, and averaging the resulting hard shadow images to compute a soft shadow image. After this precomputation, soft shadows in a static scene can be displayed in real time with simple texture mapping of the radiance textures. All pixel operations employed by the algorithm are supported in hardware by existing graphics workstations. The technique can be generalized for the simulation of shadows on specular surfaces.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: Shadow Penumbras for Complex Objects by Depth-Dependent Filtering of Multi-Layer Depth Images

paper_content:

This paper presents an efficient algorithm for filtering multi-layer depth images (MDIs) in order to produce approximate penumbras. The filtering is performed on a MDI that represents the view from the light source. The algorithm is based upon both ray tracing and the z-buffer shadow algorithm, and is closely related to convolution methods. The method's effectiveness is demonstrated on especially complex objects such as trees, whose soft shadows are expensive to compute by other methods. The method specifically addresses the problem of light-leaking that occurs when tracing rays through discrete representations, and the inability of convolution methods to produce accurate self-shadowing effects.
---
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.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: Single Sample Soft Shadows

paper_content:

A simple extension to ray tracing is presented that creates visually plausible “soft” shadows with little extra computation. Although these soft shadows are approximate, they are robust and have penumbra widths that behave in a believable way, including accurate placement of singularities where penumbra width is zero. The method has continuous behavior in space and time, so it is appropriate for both static and dynamic image generation.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: Soft shadow maps for area light by area approximation

paper_content:

Shadow mapping has been a popular way of generating shadows in real-time applications, but it is still incapable of generating realistic real time soft shadows for area light. There is an algorithm for generating soft shadows for linear light with few samples, but the algorithm is not suitable for area light. The author presents a modified method to the shadow mapping algorithm for linear light. The new method can produce convincing soft shadows for area light in real time applications.
---
paper_title: Simulating Soft Shadows with Graphics Hardware

paper_content:

Abstract : This paper describes all algorithm for simulating soft shadows at interactive rates using graphics hardware. On current graphics workstations, the technique can calculate the soft shadows cast by moving, complex objects onto multiple planar surfaces in about a second. In a static, diffuse scene, these high quality shadows can then be displayed at 30 Hz, independent of the number and size of the light sources. For a diffuse scene, the method precomputes a radiance texture that captures the shadows and other brightness variations on each polygon. The texture for each polygon is computed by creating registered projections of the scene onto the polygon from multiple sample points on each light source, and averaging the resulting hard shadow images to compute a soft shadow image. After this precomputation, soft shadows in a static scene can be displayed in real time with simple texture mapping of the radiance textures. All pixel operations employed by the algorithm are supported in hardware by existing graphics workstations. The technique can be generalized for the simulation of shadows on specular surfaces.
---
paper_title: Efficient image-based methods for rendering soft shadows

paper_content:

We present two efficient imaged-based approaches for computation and display of high-quality soft shadows from area light sources. Our methods are related to shadow maps and provide the associated benefits. The computation time and memory requirements for adding soft shadows to an image depend on image size and the number of lights, not geometric scene complexity. We also show that because area light sources are localized in space, soft shadow computations are particularly well suited to imaged-based rendering techniques. Our first approach— layered attenuation maps —achieves interactive rendering rates, but limits sampling flexibility, while our second method— coherence-based raytracing of depth images—is not interactive, but removes the limitations on sampling and yields high quality images at a fraction of the cost of conventional raytracers. Combining the two algorithms allows for rapid previewing followed by efficient high-quality rendering.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Approximate Soft Shadows on Arbitrary Surfaces using Penumbra Wedges

paper_content:

Shadow generation has been subject to serious investigation in computer graphics, and many clever algorithms have been suggested. However, previous algorithms cannot render high quality soft shadows onto arbitrary, animated objects in real time. Pursuing this goal, we present a new soft shadow algorithm that extends the standard shadow volume algorithm by replacing each shadow quadrilateral with a new primitive, called the penumbra wedge. For each silhouette edge as seen from the light source, a penumbra wedge is created that approximately models the penumbra volume that this edge gives rise to. Together the penumbra wedges can render images that often are remarkably close to more precisely rendered soft shadows. Furthermore, our new primitive is designed so that it can be rasterized efficiently. Many real-time algorithms can only use planes as shadow receivers, while ours can handle arbitrary shadow receivers. The proposed algorithm can be of great value to, e.g., 3D computer games, especially since it is highly likely that this algorithm can be implemented on programmable graphics hardware coming out within the next year, and because games often prefer perceptually convincing shadows. (Less)
---
paper_title: A geometry-based soft shadow volume algorithm using graphics hardware

paper_content:

Most previous soft shadow algorithms have either suffered from aliasing, been too slow, or could only use a limited set of shadow casters and/or receivers. Therefore, we present a strengthened soft shadow volume algorithm that deals with these problems. Our critical improvements include robust penumbra wedge construction, geometry-based visibility computation, and also simplified computation through a four-dimensional texture lookup. This enables us to implement the algorithm using programmable graphics hardware, and it results in images that most often are indistinguishable from images created as the average of 1024 hard shadow images. Furthermore, our algorithm can use both arbitrary shadow casters and receivers. Also, one version of our algorithm completely avoids sampling artifacts which is rare for soft shadow algorithms. As a bonus, the four-dimensional texture lookup allows for small textured light sources, and, even video textures can be used as light sources. Our algorithm has been implemented in pure software, and also using the GeForce FX emulator with pixel shaders. Our software implementation renders soft shadows at 0.5-5 frames per second for the images in this paper. With actual hardware, we expect that our algorithm will render soft shadows in real time. An important performance measure is bandwidth usage. For the same image quality, an algorithm using the accumulated hard shadow images uses almost two orders of magnitude more bandwidth than our algorithm. (Less)
---
paper_title: Soft shadow maps for area light by area approximation

paper_content:

Shadow mapping has been a popular way of generating shadows in real-time applications, but it is still incapable of generating realistic real time soft shadows for area light. There is an algorithm for generating soft shadows for linear light with few samples, but the algorithm is not suitable for area light. The author presents a modified method to the shadow mapping algorithm for linear light. The new method can produce convincing soft shadows for area light in real time applications.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Rendering Fake Soft Shadows with Smoothies

paper_content:

We present a new method for real-time rendering of shadows in dynamic scenes. Our approach builds on the shadow map algorithm by attaching geometric primitives that we call "smoothies" to the objects' silhouettes. The smoothies give rise to fake shadows that appear qualitatively like soft shadows, without the cost of densely sampling an area light source. The soft shadow edges hide objectionable aliasing artifacts that are noticeable with ordinary shadow maps. Our algorithm computes shadows efficiently in image space and maps well to programmable graphics hardware. We present results from several example scenes rendered in real-time.
---
paper_title: Real-Time Soft Shadows Using a Single Light Sample

paper_content:

We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by today’s graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: A geometry-based soft shadow volume algorithm using graphics hardware

paper_content:

Most previous soft shadow algorithms have either suffered from aliasing, been too slow, or could only use a limited set of shadow casters and/or receivers. Therefore, we present a strengthened soft shadow volume algorithm that deals with these problems. Our critical improvements include robust penumbra wedge construction, geometry-based visibility computation, and also simplified computation through a four-dimensional texture lookup. This enables us to implement the algorithm using programmable graphics hardware, and it results in images that most often are indistinguishable from images created as the average of 1024 hard shadow images. Furthermore, our algorithm can use both arbitrary shadow casters and receivers. Also, one version of our algorithm completely avoids sampling artifacts which is rare for soft shadow algorithms. As a bonus, the four-dimensional texture lookup allows for small textured light sources, and, even video textures can be used as light sources. Our algorithm has been implemented in pure software, and also using the GeForce FX emulator with pixel shaders. Our software implementation renders soft shadows at 0.5-5 frames per second for the images in this paper. With actual hardware, we expect that our algorithm will render soft shadows in real time. An important performance measure is bandwidth usage. For the same image quality, an algorithm using the accumulated hard shadow images uses almost two orders of magnitude more bandwidth than our algorithm. (Less)
---
paper_title: Soft shadow maps for area light by area approximation

paper_content:

Shadow mapping has been a popular way of generating shadows in real-time applications, but it is still incapable of generating realistic real time soft shadows for area light. There is an algorithm for generating soft shadows for linear light with few samples, but the algorithm is not suitable for area light. The author presents a modified method to the shadow mapping algorithm for linear light. The new method can produce convincing soft shadows for area light in real time applications.
---
paper_title: Efficient image-based methods for rendering soft shadows

paper_content:

We present two efficient imaged-based approaches for computation and display of high-quality soft shadows from area light sources. Our methods are related to shadow maps and provide the associated benefits. The computation time and memory requirements for adding soft shadows to an image depend on image size and the number of lights, not geometric scene complexity. We also show that because area light sources are localized in space, soft shadow computations are particularly well suited to imaged-based rendering techniques. Our first approach— layered attenuation maps —achieves interactive rendering rates, but limits sampling flexibility, while our second method— coherence-based raytracing of depth images—is not interactive, but removes the limitations on sampling and yields high quality images at a fraction of the cost of conventional raytracers. Combining the two algorithms allows for rapid previewing followed by efficient high-quality rendering.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: Real-Time Soft Shadows Using a Single Light Sample

paper_content:

We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by today’s graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: Single Sample Soft Shadows Using Depth Maps

paper_content:

In this paper we propose a new method for rendering soft shadows at interactive frame rates. Although the algorithm only uses information obtained from a single light source sample, it is capable of producing subjectively realistic penumbra regions. We do not claim that the proposed method is physically correct but rather that it is aesthetically correct. Since the algorithm operates on sampled representations of the scene, the shadow computation does not directly depend on the scene complexity. Having only a single depth and object ID map representing the pixels seen by the light source, we can approximate penumbrae by searching the neighborhood of pixels warped from the camera view for relevant blocker information. We explain the basic technique in detail, showing how simple observations can yield satisfying results. We also address sampling issues relevant to the quality of the computed shadows, as well as speed-up techniques that are able to bring the performance up to interactive frame rates.
---
paper_title: A geometry-based soft shadow volume algorithm using graphics hardware

paper_content:

Most previous soft shadow algorithms have either suffered from aliasing, been too slow, or could only use a limited set of shadow casters and/or receivers. Therefore, we present a strengthened soft shadow volume algorithm that deals with these problems. Our critical improvements include robust penumbra wedge construction, geometry-based visibility computation, and also simplified computation through a four-dimensional texture lookup. This enables us to implement the algorithm using programmable graphics hardware, and it results in images that most often are indistinguishable from images created as the average of 1024 hard shadow images. Furthermore, our algorithm can use both arbitrary shadow casters and receivers. Also, one version of our algorithm completely avoids sampling artifacts which is rare for soft shadow algorithms. As a bonus, the four-dimensional texture lookup allows for small textured light sources, and, even video textures can be used as light sources. Our algorithm has been implemented in pure software, and also using the GeForce FX emulator with pixel shaders. Our software implementation renders soft shadows at 0.5-5 frames per second for the images in this paper. With actual hardware, we expect that our algorithm will render soft shadows in real time. An important performance measure is bandwidth usage. For the same image quality, an algorithm using the accumulated hard shadow images uses almost two orders of magnitude more bandwidth than our algorithm. (Less)
---
paper_title: Simulating Soft Shadows with Graphics Hardware

paper_content:

Abstract : This paper describes all algorithm for simulating soft shadows at interactive rates using graphics hardware. On current graphics workstations, the technique can calculate the soft shadows cast by moving, complex objects onto multiple planar surfaces in about a second. In a static, diffuse scene, these high quality shadows can then be displayed at 30 Hz, independent of the number and size of the light sources. For a diffuse scene, the method precomputes a radiance texture that captures the shadows and other brightness variations on each polygon. The texture for each polygon is computed by creating registered projections of the scene onto the polygon from multiple sample points on each light source, and averaging the resulting hard shadow images to compute a soft shadow image. After this precomputation, soft shadows in a static scene can be displayed in real time with simple texture mapping of the radiance textures. All pixel operations employed by the algorithm are supported in hardware by existing graphics workstations. The technique can be generalized for the simulation of shadows on specular surfaces.
---
paper_title: Soft Planar Shadows Using Plateaus

paper_content:

This paper presents an algorithm for rapidly creating and rendering soft shadows on a plane. It has the advantages of rapid generation on current hard-ware, as well as high quality and a realistic feel on a perceptual level. The algorithm renders the soft shadow to a texture. It begins with a hard drop shadow, then uses the object's silhouette edges to generate penumbrae in a single pass. Though the shadows generated are physically inaccurate, this technique yields penumbrae that are smooth and perceptually convincing.
---
paper_title: Fast calculation of soft shadow textures using convolution

paper_content:

The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
---
paper_title: An optimized soft shadow volume algorithm with real-time performance

paper_content:

In this paper, we present several optimizations to our previously presented soft shadow volume algorithm. Our optimizations include tighter wedges, heavily optimized pixel shader code for both rectangular and spherical light sources, a frame buffer blending technique to overcome the limitation of 8-bit frame buffers, and a simple culling algorithm. These together give real-time performance, and for simple models we get frame rates of over 150 fps. For more complex models 50 fps is normal. In addition to optimizations, two simple techniques for improving the visual quality are also presented.
---
paper_title: Rendering Fake Soft Shadows with Smoothies

paper_content:

We present a new method for real-time rendering of shadows in dynamic scenes. Our approach builds on the shadow map algorithm by attaching geometric primitives that we call "smoothies" to the objects' silhouettes. The smoothies give rise to fake shadows that appear qualitatively like soft shadows, without the cost of densely sampling an area light source. The soft shadow edges hide objectionable aliasing artifacts that are noticeable with ordinary shadow maps. Our algorithm computes shadows efficiently in image space and maps well to programmable graphics hardware. We present results from several example scenes rendered in real-time.
---
paper_title: Real-Time Soft Shadows Using a Single Light Sample

paper_content:

We present a real-time rendering algorithm that generates soft shadows of dynamic scenes using a single light sample. As a depth-map algorithm it can handle arbitrary shadowed surfaces. The shadow-casting surfaces, however, should satisfy a few geometric properties to prevent artifacts. Our algorithm is based on a bivariate attenuation function, whose result modulates the intensity of a light causing shadows. The first argument specifies the distance of the occluding point to the shadowed point; the second argument measures how deep the shadowed point is inside the shadow. The attenuation function can be implemented using dependent texture accesses; the complete implementation of the algorithm can be accelerated by today’s graphics hardware. We outline the implementation, and discuss details of artifact prevention and filtering.
---
paper_title: A geometry-based soft shadow volume algorithm using graphics hardware

paper_content:

Most previous soft shadow algorithms have either suffered from aliasing, been too slow, or could only use a limited set of shadow casters and/or receivers. Therefore, we present a strengthened soft shadow volume algorithm that deals with these problems. Our critical improvements include robust penumbra wedge construction, geometry-based visibility computation, and also simplified computation through a four-dimensional texture lookup. This enables us to implement the algorithm using programmable graphics hardware, and it results in images that most often are indistinguishable from images created as the average of 1024 hard shadow images. Furthermore, our algorithm can use both arbitrary shadow casters and receivers. Also, one version of our algorithm completely avoids sampling artifacts which is rare for soft shadow algorithms. As a bonus, the four-dimensional texture lookup allows for small textured light sources, and, even video textures can be used as light sources. Our algorithm has been implemented in pure software, and also using the GeForce FX emulator with pixel shaders. Our software implementation renders soft shadows at 0.5-5 frames per second for the images in this paper. With actual hardware, we expect that our algorithm will render soft shadows in real time. An important performance measure is bandwidth usage. For the same image quality, an algorithm using the accumulated hard shadow images uses almost two orders of magnitude more bandwidth than our algorithm. (Less)
---

Title: A Survey of Real-time Soft Shadows Algorithms

Section 1: Introduction
Description 1: Introduce the significance of shadows in human perception of 3D space, the history of shadow studies, the relevance of soft shadows in real-time graphics, and outline the structure of the survey.

Section 2: What is a shadow?
Description 2: Explain the basic concepts of shadows, differentiate between umbra, penumbra, attached shadows, and cast shadows, and emphasize the importance of these distinctions.

Section 3: Importance of shadow effects
Description 3: Illustrate the roles shadows play in understanding 3D geometry, object positions, and sizes through concrete examples and visual cues in complex scenes.

Section 4: Hard shadows vs soft shadows
Description 4: Discuss the differences between hard and soft shadows, their respective generation techniques, and the challenges associated with creating realistic soft shadows.

Section 5: Composition of multiple shadows
Description 5: Address the complexities of combining shadows from multiple light sources and occluders, and the issues arising from partial visibility functions.

Section 6: Physically exact or fake shadows
Description 6: Explore methods for simulating soft shadows using approximations or physically accurate techniques and the compromises involved.

Section 7: Real-time
Description 7: Examine the criteria for defining "real-time" in graphic applications, the importance of maintaining high frame rates, and the adaptability of shadow algorithms to different performance levels.

Section 8: Shadows of special objects
Description 8: Discuss special treatment required for complex volumetric objects like clouds, hair, and grass in shadowing algorithms.

Section 9: Constraints on the scene
Description 9: Highlight constraints shadowing algorithms may impose on the scene, such as object models and the identification of occluders or receivers.

Section 10: Basic techniques for real-time shadows
Description 10: Describe the fundamental methods for real-time shadow generation, focusing on shadow maps and shadow volumes.

Section 11: Image-based approach
Description 11: Present image-based algorithms for producing soft shadows, building on shadow map techniques.

Section 12: Object-based approach
Description 12: Detail object-based algorithms for generating soft shadows, building on shadow volume techniques.

Section 13: Controlling the time
Description 13: Identify parameters and methods for tuning the time required for shadow generation to maintain real-time processing.

Section 14: Controlling the aspect
Description 14: Discuss methods for tuning the visual quality and accuracy of the shadows produced by different algorithms.

Section 15: Number and shape of the light sources
Description 15: Examine assumptions and constraints related to the number, shape, and field of emission of light sources in shadow algorithms.

Section 16: New generation of GPUs
Description 16: Explore the potential and requirements of modern GPUs for real-time soft shadow algorithms.

Section 17: Conclusions
Description 17: Summarize the surveyed algorithms, discuss their advantages and drawbacks, and suggest future directions for real-time soft shadow rendering.