>whether my generated triangle in the marching cubes algorithm
>is a fornt face triangle or not without using cross product to
>check the sign of its normal... is there any other way?
This depends completely on the way you''re computing the triangles!
I suggest using some precalculated triangle table for this purpose, for example the tables on Paul Bourke''s site
>about the second one , i think its nice one , but i thought
>about another one... some triangles share 2 vertiecs , so whats
>happening is that sometimes i calcuate the normal for the same
>vertex twise instead of once... what i can do is to check
>whether i already calculated the normal in this vertex or
>not... it would save some CPU time.
Here''s a good trick from "the good ol'' days":
The problem with checking is that you first need to reinitialize the test array per frame. To overcome N^3 iterations, initialize an array that tells on which frame a cell has been checked for the last time. If you ever encounter "the current frame" in some particulal cell, you can assume that it has been already checked on the current frame.
You might use values of -1 for initializing this table, and use the largest possible datatype in hand. Even int is good because you probably won''t compute more than 2,000,000,000 frames of animation...
- Mikko Kauppila
