We present a new, real-time method for rendering diffuse and glossy objects in low-frequency lighting environments that captures soft shadows, interreflections, and caustics. As a preprocess, a novel global transport simulator creates functions over the object's surface representing transfer of arbitrary, low-frequency incident lighting into transferred radiance which includes global effects like shadows and interreflections from the object onto itself. At run-time, these transfer functions are applied to actual incident lighting. Dynamic, local lighting is handled by sampling it close to the object every frame; the object can also be rigidly rotated with respect to the lighting and vice versa. Lighting and transfer functions are represented using low-order spherical harmonics. This avoids aliasing and evaluates efficiently on graphics hardware by reducing the shading integral to a dot product of 9 to 25 element vectors for diffuse receivers. Glossy objects are handled using matrices rather than vectors. We further introduce functions for radiance transfer from a dynamic lighting environment through a preprocessed object to neighboring points in space. These allow soft shadows and caustics from rigidly moving objects to be cast onto arbitrary, dynamic receivers. We demonstrate real-time global lighting effects with this approach.

Recent advances in GPU technology have produced a shift in focus for real-time rendering applications, whereby improvements in image quality are sought in addition to raw polygon display performance. Rendering effects such as antialiasing, motion blur and shadow casting are becoming commonplace and will likely be considered indispensable in the near future. The last complete and famous survey on shadow algorithms — by Woo et al. 52 in 1990 — has to be updated in particular in view of recent improvements in graphics hardware, which make new algorithms possible. This paper covers all current methods for real-time shadow rendering, without venturing into slower, high quality techniques based on ray casting or radiosity. Shadows are useful for a variety of reasons: first, they help understand relative object placement in a 3D scene by providing visual cues. Second, they dramatically improve image realism and allow the creation of complex lighting ambiances. Depending on the application, the emphasis is placed on a guaranteed framerate, or on the visual quality of the shadows including penumbra effects or “soft shadows”. Obviously no single method can render physically correct soft shadows in real time for any dynamic scene! However our survey aims at providing an exhaustive study allowing a programmer to choose the best compromise for his/her needs. In particular we discuss the advantages, limitations, rendering quality and cost of each algorithm. Recommendations are included based on simple characteristics of the application such as static/moving lights, single or multiple light sources, static/dynamic geometry, geometric complexity, directed or omnidirectional lights, etc. Finally we indicate which methods can efficiently exploit the most recent graphics hardware facilities.

Analytic visibility algorithms, for example methods which compute a subdivided mesh to represent shadows, are notoriously unrobust and hard to use in practice. We present a new method based on a generalized definition of extremal stabbing lines, which are the extremities of shadow boundaries. We treat scenes containing multiple edges or vertices in degenerate configurations, (e.g., collinear or coplanar). We introduce a robust ɛ method to determine whether each generalized extremal stabbing line is blocked, or is touched by these scene elements, and thus added to the line's generators. We develop robust blocker predicates for polygons which are smaller than ɛ. For larger ɛ values, small shadow features merge and eventually disappear. We can thus robustly connect generalized extremal stabbing lines in degenerate scenes to form shadow boundaries. We show that our approach is consistent, and that shadow boundary connectivity is preserved when features merge. We have implemented our algorithm, and show that we can robustly compute analytic shadow boundaries to the precision of our chosen ɛ threshold for non-trivial models, containing numerous degeneracies.

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.

Figure 1: A scene including alpha-textured meshes (foliage and wire netting). Left: illustration of realistic soft shadows produced by the average of 1024 hard shadows (2.5s per frame). Right: our new soft shadow algorithm rendering the same scene at 25 fps without any precomputation. We present a new real-time soft shadow algorithm using a single shadow map per light source. Therefore, our algorithm is well suited to render both complex and dynamic scenes, and it handles all rasterizable geometries. The key idea of our method is to use the shadow map as a simple and uniform discretized represention of the scene, thus allowing us to generate realistic soft shadows in most cases. In particular it naturally handles occluder fusion. Also, our algorithm deals with rectangular light sources as well as textured light sources with high precision, and it maps well to programmable graphics hardware. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and RealismColor, shading, shadowing, and texture

Previous methods for soft shadows numerically integrate over many light directions at each receiver point, testing blocker visibility in each direction. We introduce a method for real-time soft shadows in dynamic scenes illuminated by large, low-frequency light sources where such integration is impractical. Our method operates on vectors representing low-frequency visibility of blockers in the spherical harmonic basis. Blocking geometry is modeled as a set of spheres; relatively few spheres capture the low-frequency blocking effect of complicated geometry. At each receiver point, we compute the product of visibility vectors for these blocker spheres as seen from the point. Instead of computing an expensive SH product per blocker as in previous work, we perform inexpensive vector sums to accumulate the log of blocker visibility. SH exponentiation then yields the product visibility vector over all blockers. We show how the SH exponentiation required can be approximated accurately and efficiently for low-order SH, accelerating previous CPUbased methods by a factor of 10 or more, depending on blocker complexity, and allowing real-time GPU implementation.

We present a soft shadow technique for dynamic scenes with moving objects under the combined illumination of moving local light sources and dynamic environment maps. The main idea of our technique is to precompute for each scene entity a shadow field that describes the shadowing effects of the entity at points around it. The shadow field for a light source, called a source radiance field (SRF), records radiance from an illuminant as cube maps at sampled points in its surrounding space. For an occluder, an object occlusion field (OOF) conversely represents in a similar manner the occlusion of radiance by an object. A fundamental difference between shadow fields and previous shadow computation concepts is that shadow fields can be precomputed independent of scene configuration. This is critical for dynamic scenes because, at any given instant, the shadow information at any receiver point can be rapidly computed as a simple combination of SRFs and OOFs according to the current scene configuration. Applications that particularly benefit from this technique include large dynamic scenes in which many instances of an entity can share a single shadow field. Our technique enables low-frequency shadowing effects in dynamic scenes in real-time and all-frequency shadows at interactive rates.

Shadow computation in dynamic scenes under complex illumination is a challenging problem. Methods based on precomputation provide accurate, real-time solutions, but are hard to extend to dynamic scenes. Specialized approaches for soft shadows can deal with dynamic objects but are not fast enough to handle more than one light source. In this paper, we present a technique for rendering dynamic objects under arbitrary environment illumination, which does not require any precomputation. The key ingredient is a fast, approximate technique for computing soft shadows, which achieves several hundred frames per second for a single light source. This allows for approximating environment illumination with a sparse collection of area light sources and yields real-time frame rates.

In this paper, we propose a real-time method for rendering soft shadows and inter-reflections of dynamic objects under complex illumination. In previous methods, many efforts were taken to acquire occlusion and reflection informations for dynamic scene on the fly, and the result image cannot be generated in real time. In our approach, these informations for each object are pre-computed and stored in well-defined Spherical Radiance Transport Maps (SRTMs). For distant complex illumination such as environment illumination and area light source, we decompose the illumination to several hundred directional lights. In rendering, we search in SRTMs for occlusion info which may cause shadows, and reflection info which may cause inter-reflections. Finally we produce realistic soft shadows and inter-reflections efficiently. Our method is related with but different from previous Pre-computed Radiance Transfer techniques which are only suitable for static scene. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: shading and shadowing 1.

We present a technique for interactive rendering of glossy objects in complex and dynamic lighting environments that captures interreflections and all-frequency shadows. Our system is based on precomputed radiance transfer and separable BRDF approximation. We factor glossy BRDFs using a separable decomposition and keep only a few low-order approximation terms, each consisting of a purely view-dependent and a purely light-dependent component. In the precomputation step, for every vertex we sample its visibility and compute a direct illumination transport vector corresponding to each BRDF term. We use modern graphics hardware to accelerate this step, and further compress the data using a non-linear wavelet approximation. The direct illumination pass is followed by one or more interreflection passes, each of which gathers compressed transport vectors from the previous pass to produce global illumination transport vectors. To render at run time, we dynamically sample the lighting to produce a light vector, also represented in a wavelet basis. We compute the inner product of the light vector with the precomputed transport vectors, and the results are further combined with the BRDF view-dependent components to produce vertex colors. We describe acceleration of the rendering algorithm using programmable graphics hardware, and discuss the limitations and tradeoffs imposed by the hardware.