Not heard of OSPRay, interesting.
I personally think Mitsuba is the dark horse of free renderers. Blazing fast, good highly modular design, good docs, super easy Python bindings, GPU preview. The only problem is it's a one-man show, and the one man seems to have been doing other things lately. Nevertheless it's the renderer I think deserves to become the "standard".
Re:Blender 2.79: OpenCL on par with CUDA
by glenneroo on Wednesday April 12, 2017 @08:40PM
(#14103071)
I don't know about API access, but there are a couple more external renderers listed here: https://www.blender.org/download/external-renderers/
The nicest renderer I've found, API-wise, was OSPRay, which was simple and elegant to use... but doesn't support volumetric rendering in any way. I have in the past got this working, more or less, with Mitsuba with some custom code but I'd rather like to avoid customisations. They're too much work to maintain.