Abstract: The described systems and methods are directed at interactively rendering graphics using precomputed radiance transfer (PRT). A reflectance matrix that represents the reflectance of a particular object to be rendered is determined. Source lighting associated with the object is represented using basis functions. The reflectance matrix is factored into view and light components. A raw transfer matrix is determined based, in part, from the factored reflectance matrix and the source lighting. The raw transfer matrix is partitioned to obtain transfer matrices, which are used to render the object. The described systems and methods are capable of rendering glossy objects with well-defined shadows.

Abstract: Shadows, which play an important role in perceiving the shape and texture of an object, are simulated interactively in a real time, self-shadowing of a bump mapped surface for a computer rendered object. A computer graphics textured object function defines a horizon map over an orientation in a tangent space of the object using different textures or basis functions. The implementation can be performed using commodity graphics hardware by precomputing the horizon map for limited visibility for each point on the bump mapped surface given light in each of a plurality of radial directions. The horizon map is used to produce self-shadowing of the bump mapped surface of the object.

Abstract: A hardware-accelerated process of computing radiance transfer coefficients (such as for use in image rendering based on precomputed radiance transfer (PRT) techniques) is re-ordered as compared to previously known PRT precomputations to iterate over a sampling of directions about an object. The hardware-accelerated process uses a set of textures representing positions and normals for a sampling of points over a modeled object. In iterating over the directions, the process computes the depth of the object in a shadow buffer, then computes a texture of the radiance contribution based on the normal and position textures and depth from the shadow buffer. The resulting radiance contribution textures of the iterated directions are accumulated to produce a texture representing the radiance transfer coefficients of the sampled positions. This enables the process to avoid reduction operations, ray tracing and slow read-back path limitations of graphical processing units.

Abstract: Computer graphics image rendering techniques render images modeling transfer at two scales. A macro-scale is coarsely sampled over an object's surface, providing global effects like shadows and interreflections cast from an arm onto a body. A meso-scale is finely sampled over a small patch to provide local texture. Low-order spherical harmonics represent low-frequency lighting dependence for both scales. To render, a coefficient vector representing distant source lighting is first transformed at the macro-scale by a matrix at each vertex of a coarse mesh, resulting in vectors representing a spatially-varying hemisphere of lighting incident to the meso-scale. A radiance transfer texture specifies the meso-scale response to each lighting basis component, and a function of a spatial index and a view direction. A dot product of the macro-scale result vector with the vector looked up from the radiance transfer texture performs the correct shading integral.

Abstract: The present invention is directed to systems and methods for all-frequency relighting by representing low frequencies of lighting with spherical harmonics and approximate the residual high-frequency energy with point lights. One such embodiment renders low-frequencies with a precomputed radiance transfer (PRT) technique (which requires only a moderate amount of precomputation and storage), while the higher-frequencies are rendered with on-the-fly techniques such as shadow maps and shadow volumes. In addition, various embodiments are directed to a systems and methods for decomposing the lighting into harmonics and sets of point lights. Various alternative embodiments are directed to systems and methods for characterizing the types of environments for which the described decomposition is a viable technique in terms of speed (efficiency) versus quality (realism).

Abstract: The present invention is directed to a enhanced Precomputed Radiance Transfer (PRT) system employing an algorithm to compute a PRT signal over a surface mesh and subdividing facets of the mesh to increase the number of surface vertices such that the spatial variation of the transfer signal is resolved sufficiently everywhere on the surface. The method of this system ensures that radiance transfer shading produces colors of sufficient accuracy all over the surface. In certain embodiments, transfer is computed only at surface vertices, although this does result in a certain amount of acceptable aliasing and blurring of surface lighting detail in regions where the tessellation is too coarse. Furthermore, the method comprises a spatial and density sampling techniques that measures the transfer signal to a desirable appropriate resolution while minimizing aliasing. Once computed, the signal is represented as compactly as possible to minimize storage and runtime computation requirements.

Abstract: Real-time processing includes per-point transfer matrices forming a high-dimensional surface signal that is compressed using clustered principal component analysis (CPCA). CPCA partitions multiple samples into fewer clusters, each cluster approximating the signal as an affine subspace. Further, source radiance is input to a processor, which approximates source radiance using spherical harmonic basis to produce a set of source radiance coefficients. A graphics processing unit (GPU) processes the source radiance coefficients through the transfer matrix model for each cluster. The result of such processing is the exit radiance, which parameterizes the radiance leaving the surface of the object at each point, thus producing the shading for each point of the virtual object in real time.

Abstract: Shadows, which play an important role in perceiving the shape and texture of an object, are simulated interactively in a real time, self-shadowing of a bump mapped surface for a computer rendered object. A computer graphics textured object function defines a horizon map over an orientation in a tangent space of the object using different textures or basis functions. The implementation can be performed using commodity graphics hardware by precomputing the horizon map for limited visibility for each point on the bump mapped surface given light in each of a plurality of radial directions. The horizon map is used to produce self-shadowing of the bump mapped surface of the object.