Interactive Ray Tracing Using Hardware Accelerated Image-Space Methods

In recent years, interactive ray tracing has become realisable, albeit mainly using clustered workstations and sophisticated acceleration structures. On nonclustered computer architectures this is still not an easy task to achieve, especially when rendering animated scenes, even though the computation power of modern workstations is increasing rapidly. In this paper we propose commonly known image-space rendering techniques to be used in the context of ray tracing. We describe a visibility preprocessing algorithm to perform interactive ray tracing based on the standard depth testing capability of graphics processing units. This method – item buffer rendering – is particularly suitable for rendering animated scenes, as it completely avoids the necessity of creating and updating any kind of spatial acceleration structure in order to achieve high frame rates. The item buffer stores indices referencing those primitives which are visible in screen-space. Primary ray intersection testing can therefore be executed very efficiently by performing only one primitive lookup operation and one intersection test. As a consequence, this approach reduces the total number of primary ray intersection tests to a minimum. Additionally we integrate shadow rendering into our ray tracer using the shadow mapping technique to avoid computationally expensive shadow rays. We compare CPU and GPU based implementations of our ray tracer and analyse the advantages and disadvantages of both approaches in terms of visual quality and rendering performance. CR