tow basic questions

[zydgyy]

Hi,
1)i read about there are two methods to determine which face of a polygon is up,by specifying a normal verctor and by specifying wounding orientation of vertices(clock-wise or counter-clock wise)!How do i know which method do i use and when?
2)I dont really understand why the color-tracking is the preferred than calling glMaterail...
Thank u~

[V-man]

1) why do you want to know if a polygon is up? What do you plan to do with that information?

2) They don't mater anymore. They are part of old GL and old GPUS (10 years ago). Technology has changed. Now (actually, since 2002), everything is shaders.

[zydgyy]

1)it just coufuse me,if i use a normal to specify which way is out and it is inverted as the wound-order,what hanppend?

[V-man]

The normal vector effects the lighting.
Also, there are some cases that use the normal vector such as in texture coord generation => GL_SPHERE_MAP and GL_NORMAL_MAP and GL_REFLECTION_MAP
http://www.opengl.org/wiki/Mathematics_of_glTexGen