The demand for ever-increasing visual fidelity in computer graphics has led to the development of incredibly powerful hardware. Current graphics processors are highly parallel devices that can process thousands of individual work items using hundreds of individual cores. Graphics devices have also become more flexible. While early GPUs used very specialized hardware to solve very specific render tasks quickly, later hardware has become more and more programmable to the point where current GPUs can be considered general-purpose compute hardware with some added functionality specific to rendering problems.
This is why it is now becoming common to use graphics hardware for performing tasks other than rendering. Thus APIs specialized for programming these general-purpose applications on graphics hardware like OpenCL or CUDA have been developed. This new flexibility also makes it feasible to step away from the classic real-time graphics pipeline based on polygon rasterization and think about implementing alternative rendering algorithms on these powerful devices.
One domain to look for such alternative approaches is in production rendering, which is the branch of computer graphics that is concerned with creating visuals for film and print. These applications usually require very high image quality in terms of detail and freedom from visual artifacts. The rendering algorithm that is most commonly associated with production rendering is Reyes.
While the real-time rendering pipeline can only draw scenes composed of planar triangles and polygons, Reyes is able to draw arbitrary curved surfaces without any visible artifacts. It does this by tessellating the surfaces into sub-pixel sized polygons, which are then drawn to the screen. Using these tiny polygons – also called micropolygons – as intermediate representation allows rendering a large array of different, possibly displaced surface types without any geometric artifacts while using a single back-end for shading and sampling. Reyes performs surface shading on the polygon-level, with the sampler only performing simple color interpolation. De-coupling shading from surface sampling also allows for higher-order rasterization techniques like for instance stochastic rasterization of motion blur.
The flexibility of Reyes and the fact that many content pipelines for production rendering are tooled for this algorithm make it an interesting candidate for implementation on the GPU. Having a full micropolygon rendering pipeline running on graphics hardware would allow for some very impressive visuals. It would also free artists from some performance optimization tasks necessary when designing assets for current graphics pipelines. A GPU-accelerated version of Reyes would also be invaluable for production rendering artists, since it would allow them to do more rapid design iterations.
