开始设计elvish ray Interface Specification
暂时还是interface的设计，不包含具体算法等...
这是开发开源渲染器的第一步...
我们的团队已经初步组成，还在不断扩大中，需要一个规范，才能统一开发...
需要参考的东西有：
max SDK
Maya API
http://wiki.blender.org/index.php/Render_API
http://softimage.wiki.avid.com/index.php/Custom_Renderers_%28XSISDK%29
RenderMan Interface Specification
mental ray API
Gelato Techical Specification
Cg Specification
GLSL Specification
Houdini API
可以参考的算法：
http://www.toxicengine.org/
Pixie
Aqsis
povray
yafray
PBRT
renderbitch
http://radsite.lbl.gov/radiance/
http://www.cs.kuleuven.be/cwis/research/graphics/RENDERPARK/
rayshade
OpenRT
BMRT
http://homepages.paradise.net.nz/nickamy/simpleraytracer/simpleraytracer.htm
http://homepages.paradise.net.nz/nickamy/raytracer/raytracer.htm
http://www.winosi.onlinehome.de/
Vision An Architecture for Physically-Based Rendering
