Added Vector#lerp

lib/cyberarm_engine.rb

@@ -1,5 +1,5 @@
 begin
-  require "../ffi-gosu/lib/gosu"
+  require File.expand_path("../../ffi-gosu/lib/gosu", File.dirname(__FILE__))
 rescue LoadError => e
   pp e
   require "gosu"

lib/cyberarm_engine/lib/vector.rb

@@ -162,6 +162,10 @@ module CyberarmEngine
       @x + @y + @z
     end
 
+    def lerp(other, factor)
+      (self - other) * factor.clamp(0.0, 1.0)
+    end
+
     # 2D distance using X and Y
     def distance(other)
       Math.sqrt((@x-other.x)**2 + (@y-other.y)**2)