New wisdom on offline/interactive rendering

* Tracing rays is fast, shading is slow

* Normalize is slow and shoshould be avoided as much as possible

* C is not faster than C ++, correct use of C ++ features can improve performance

* SSE is not always faster, shocould be used without load and store from FPU

* Taking branch is slower, computation is faster

* Computation is fast, Accessing memory is slow

* Do not stuck the stack memory, make best use of registers

* Write clean code, optimize when the code is clean enough

* Always use a profiler, the bottleneck is not what you expect CT for most of the time