OpenMW

OpenMW is a remake of the open world rpg Morriwnd. The remake is a mix of D and C++, which is unfortunately a bit of a pain to write interfaces between. The rendering library used is Ogre3D

I was involved in writing the terrain rendering component. It was written in C++, using a Quadtree based on these landscape rendering papers

The hardest part was actually trying to get it to work at a decent frame rate. At the highest detail quad level, the terrain used texture splatting rather than a per-rendered image. Unfortunately the data files allowed for a total of 256 different textures per quad, effectively meaning a maximum of 255 passes. We were aiming for low powered GPUs which means that we couldn't use fragment shaders to reduce it, and while it could be reduced using a graphics card with more texture units (Modern ones have 8 - 16) mine only has 2.
Even when it has 8 or so different textures per quad, performance ended up fairly terrible. In the end I broke the lowest quad into 16 pieces and while it meant that in total there would be more possible passes, in practice the frustum culling reduced them to an acceptable level.