Abstract
Recent work on distributed ray tracing algorithms using the Distributed Array Processor (DAP) will be described. It is shown that ray tracing algorithms are ideally suited to SIMD processor arrays because, once a set of rays has been cast from the viewpoint through pixels in the image plane, the origin and direction vectors which parameterise each ray after successive reflections can be mapped uniformly to the DAP processor array. Assigning one ray per processing element in this manner allows 64 x 64 = 4096 rays to be traced simultaneously. No local neighbourhood operations within the processor array are required because each ray can be traced independently. Thus, arbitrarily large images can easily be generated by repeatedly casting 64 x 64 bundles of rays with the appropriate origin and direction vectors.
Objects in the scene are modeled using quadric primitives which are combined using the regularised set operations of constructive solid geometry (CSG). Quadrics were chosen because they are straightforward to describe mathematically and facilitate calculation of the ray-surface intersections and also surface normals required for shading calculations. Each of the twelve canonical quadric forms is represented by a 4 x 4 matrix which can be rotated, scaled and translated as desired. Although in the current version each transformation is carried out using parallel matrix multiplication, the small size of the transformation matrices means that inefficient use is made of the processor array. We therefore suggest an improved method whereby all quadric primitives can be transformed in parallel.
Using the 1:1 mapping of ray parameters to processing elements as suggested, the IN-OUT classification resulting from ray intersections with any quadric primitive or combine operation node in the binary CSG tree can be evaluated in parallel for an entire ray bundle. Thus, although the binary CSG tree must be serially traversed, the operations required at each node may be performed in parallel for a given ray bundle. This approach can therefore be regarded as ’primitive-serial, ray parallel’.
Using an SIMD processor array in conjunction with the parallel algorithms suggested here, highly realistic graphics images can be produced in very short run-times.
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© 1988 Springer-Verlag Berlin Heidelberg
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Williams, N.S., Buxton, B.F., Buxton, H. (1988). Distributed Ray Tracing Using an SIMD Processor Array. In: Earnshaw, R.A. (eds) Theoretical Foundations of Computer Graphics and CAD. NATO ASI Series, vol 40. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-83539-1_27
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DOI: https://doi.org/10.1007/978-3-642-83539-1_27
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