This new algorithm, based on GPUs, can compute ambient occlusion to inexpensively approximate global-illumination effects in real-time systems and games. The first step in deriving this algorithm is to examine how ambient occlusion relates to the physically founded rendering equation. The correspondence stems from a fuzzy membership function that defines what constitutes nearby occlusions. The next step is to develop a method to calculate ambient occlusion in real time without precomputation. The algorithm is based on a novel interpretation of ambient occlusion that measures the relative volume of the visible part of the surface's tangent sphere. The new formula's integrand has low variation and thus can be estimated accurately with a few samples.

This paper examines the efficiency of different rayshooting acceleration schemes, including the uniform space subdivision, octree and kd-tree. We use simple computational models, which assume that the objects are uniformly distributed in space. The efficiency is characterized by two measures, including the expected number of ray-object intersections needed to identify the firstly intersected object, and the expected number of steps on the space partitioning data structure. We can come to the interesting conclusion that these numbers are constant and are independent of the number of objects in the scene. The number of intersections is determined by how well the cells of the partitioning data structure enclose the objects. Such analysis helps to understand why kd-tree is better than octree and uniform space subdivision and provides hints to improve their implementation.

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This paper presents a hatching algorithm which -while also allows for an implementation in real-time -is integrated into the production pipeline of computer generated motion picture. Motion picture production pipelines impose special functional and quality requirements. From the functional point of view, the stages of modeling, 3D rendering, and compositing form a pipeline without feed-back, and frames are rendered independently, possibly on different computers. Thus, no temporal data can be shared between them while flicker free animation needs to be generated. Quality requirements can be grasped as that of dual consistency: the generated hatching must consistently follow object movement and deformation, and, at the same time, it should have a consistent pattern and density in image-space to provide the hand-crafted look. In order to meet both requirements, we apply a particle based method and develop an image-space density control mechanism using rejection sampling and lowdiscrepancy sequences. We also discuss the decomposition of rendering tasks according to the main stages of the production pipeline and demonstrate how the artist can define the illustration style in a convenient way.

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