Add short-range vertex-based pathfinder.
Integrate new pathfinder into unit motion code.
Change obstruction system to get rid of circles, and differentiate
structures from units.
Make PositionChanged messages synchronous.
Try to prevent some accidental float->int conversions.
This was SVN commit r7484.
Giant merge from
http://svn.wildfiregames.com/hg-source/file/5fb522019d5e
Infrastructure is largely complete, gameplay is largely missing
Disabled by default; use command-line flag "-sim2"
(Second attempt at commit...)
This was SVN commit r7259.
