My test of raycasting, voxels, and learning the D programming language all at once; a failure bound to happen.
Partly based on the source code of the Rearview engine.
http://rearview.sourceforge.net/
http://sourceforge.net/projects/rearview/
Also based on tutorials from here:
https://sites.google.com/site/letsmakeavoxelengine/
http://permadi.com/1996/05/ray-casting-tutorial-table-of-contents/