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.

We have implemented an image combining architecture that allows distributed rendering of a partitioned data set at interactive rates. The architecture achieves real-time frame rates and low latency through pipelining and the use of a high bandwidth network technology to transfer the image data. It is flexible because it uses programmable FPGA devices to implement the combining logic. The implementation cost is kept low by using only commodity components for the network and graphics, and FPGA logic. The result is a cost-effective interactive visualization system that can be used with a variety of applications running on distributed computing systems such as cluster of workstations and personal computers. We first motivate the development of a distributed rendering system and we introduce some of the concepts related to the 3D-visualization domain. We then describe our implementation of this system using the PCI Pamette FPGA-based board. We emphasize the advantages of using a programmable board for the prototype development and also for a potential commercial version.