Hi C-A,
Terragen does some things that few other renderers can - particularly extreme displacement of large surfaces - and this means that many algorithms have to be adapted or completely redesigned to work in fairly uncharted domains.
A Global Illumination system can rarely be labelled with just one term. They are a combination of multiple algorithms which each aim to solve a different aspect of the overall global illumination problem. Terragen does apply Monte Carlo principles, but I have taken a few liberties. Many improvements could be made to make it statistically more correct and give much higher quality results in a shorter time, but most of the development time has gone into developing a proprietary GI lighting cache (loosely based on the idea behind an Irradiance Cache, but with an emphasis on improving the kind of appearance of very rough surfaces) and interfacing it all with very large procedural landscapes. Actually that second part is the most difficult because of the huge complexity of the procedural model. Developing a renderer is as much an art as it is a science (or so I like to tell myself
), and you can't always lift existing techniques and apply them directly if the renderer has a lot of unusual technology. But there is certainly an endless supply of research which could directly benefit Terragen, given enough time and resources.
You should also consider the possibility that maybe Terragen isn't really as slow as you think it is, for what it is doing in some scenes. For what that's worth
I know it would be a much better product if render times could be significantly reduced, and with the new update we've made many changes to improve its ability to work at higher resolutions where Terragen has tended to suffer the most.
Matt
