So, I have decided to use polygons (!) but only to render the quasi-voxels - its just easier and faster than messing with ray-traced volumes. Also dumped QT -- too bloaty for my needs; just using barebones (cross-platform) libraries. Here is a shot of a landscape and another two shots with just lighting (click for enlarged version). This uses Simplex Noise, Voronoi Noise, and just Plain Old Noise (TM). Also features ambient occlusion and shadows, on a per-voxel-thing basis. Also loads a virtually infinite landscape over time. Last but not least, I just added in multithreading - it maxes out every core, and I must say performance just skyrocketed after that (partly due to the fact that processing chunks no longer blocks the main thread). I wrote it in a few days. Uh, yeah it looks like a crappy version of Minecraft, you want to fight about it?