Katsuhiko Hirota

Incremental Ray Tracing

We have developed a method to reduce the ray tracing time that recomputes or updates only the changed parts of the image for a fixed viewpoint for a dynamic sequence of images. This method enables a designer to make small changes in geometry or surface properties of a ray-traced scene without recalculating the entire image. The intersection tree is extended to contain the intersection point, surface normal, and related data that records the path through which the ray propagated using a voxel partition scheme. These descriptions are then used during the update to quickly determine which parts of the image need recomputation and to reduce the number of recomputations. The key idea behind the method is to localize the influence of changed objects using the voxel partition and to minimize the access cost of the data structures. Testing if a ray is changed by the changed objects is done with a hash index, which represents the ray’s path. Intersection recalculation to determine a changed ray’s new visible point can be reduced with information saved in the intersections. The optimal tree traversal algorithm limits the parts of the data structures to be accessed so that traversal cost is minimized. This method was developed on the CAP (Cellular Array Processor) parallel processor. An implementation approach that accounts for data storage and load balancing is also presented. The results demonstrate great performance improvements over calculating an entirely new rendering. With this method ray tracing may become practical for some computer graphics applications, such as CAD and animation which require high-quality images.

Fast image generation of construcitve solid geometry using a cellular array processor

A general purpose Cellular Array Processor(CAP) with distributed frame buffers for fast parallel subimage generation has been developed. CAP consists of many processor elements called cells. A cell has video memory for subimage storage, a window controller to map each subimage to an area on the monitor screen, and communication devices, in addition to ordinary microcomputer components such as MPU, RAM, and ROM. Image data in a cell is directly displayed via the video bus. The mapping pattern and the position on the screen of subimages can be changed dynamically. Various hidden surface algorithms can be implemented in CAP using mapping patterns appropriate for the algorithm.Our goal is an efficient interactive visual solid modeler. We adopted a general CSG hidden surface algorithm that enables display of both Boundary representation and Constructive Solid Geometry. A technique for hidden surface removal of general CSG models, requiring less memory space for large models in many cases, has been proposed. This technique subdivides the model into submodels by dividing the CSG tree at union nodes. Imagse of each submodel are generated by a CSG or a z-buffer algorithm. If a submodel is just a primitive, it is processed by the z-buffer algorithm, otherwise by the CSG algorithm. Hidden surface removal between submodels is done by comparing the z values for each pixel which are saved in the z-buffer.