unity rendering, maps, PBR, NPR
unity rendering pipeline
https://docs.unity3d.com/Manual/SL-RenderPipeline.html
lighting and rendering in unity 5
https://unity3d.com/cn/learn/tutorials/topics/graphics/introduction-lighting-and-rendering?playlist=17102
normal mapping
http://wiki.polycount.com/wiki/Normal_map
PBR
https://blogs.unity3d.com/2015/02/18/working-with-physically-based-shading-a-practical-approach/
displacement map vs height map vs parallax map
http://gamedev.stackexchange.com/questions/65755/whats-the-difference-between-displacement-mapping-and-height-mapping
https://developer.valvesoftware.com/wiki/Parallax_mapping
https://developer.valvesoftware.com/wiki/Heightmap
http://blog.digitaltutors.com/bump-normal-and-displacement-maps/
fresnel
http://filmicgames.com/archives/557
在真实世界中，除了金属之外，其它物质均有不同程度的“菲涅尔效应”。视线垂直于表面时，反射较弱，而当视线非垂直表面时，夹角越小，反射越明显。如果你看向一个圆球，那圆球中心的反射较弱，靠近边缘较强。不过这种过度关系被折射率影响。
如果你站在湖边，低头看脚下的水，你会发现水是透明的，反射不是特别强烈；如果你看远处的湖面，你会发现水并不是透明的，但反射非常强烈。这就是“菲涅尔效应”。这就是反射/折射与视点角度之间的关系。
不同材质的菲涅尔效应强弱不同，导体(如金属)的菲涅尔反射效应很弱，就拿铝来说，其反射率在所有角度下几乎都保持在86%以上，随角度变化很小，而绝缘体材质的菲涅尔效应就很明显，比如折射率为1.5的玻璃，在表面法向量方向的反射率仅为4%，但当视线与表面法向量夹角很大的时候，反射率可以接近100%，这一现象也使得金属与非金属看起来不同。
grazing angle When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface, rather than that between the beam and the surface normal, in other words 90° minus the angle of incidence. This small angle is called a glancing angle or grazing angle. Incidence at grazing angles is called "grazing incidence".
diffuse vs albedo
An albedo map defines the color of diffused light. One of the biggest differences between an albedo map in a PBR system and a traditional diffuse map is the lack of directional light or ambient occlusion. Directional light will look incorrect in certain lighting conditions, and ambient occlusion should be added in the separate AO slot.
The albedo map will sometimes define more than the diffuse color as well, for instance, when using a metalness map, the albedo map defines the diffuse color for insulators (non-metals) and reflectivity for metallic surfaces.
NPR
http://www.cs.utah.edu/~shirley/papers/gooch98.pdf
Illustrative Rendering In Team Fortress2
http://www.valvesoftware.com/publications/2007/NPAR07_IllustrativeRenderingInTeamFortress2.pdf
http://blog.csdn.net/candycat1992/article/details/37696187
https://developer.valvesoftware.com/wiki/Half_Lambert