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