   what is geometry primitives?
  I know plane line triangle aabb circle ...is geometry primitives.but point normal etc is geometry primitives too?   
  As mathematical concepts, they are, since they are basic elements used to describe more complex objects.However, a primitive also has another meaning in computational geometry: it is a simple object that can be drawn by the renderer. Usually, primitives are: point, line, line strip, triangle, triangle strip, triangle fan, and quad. Normals are not primitives (they represent a property of a primitive or of part of a primitive, just like a color or a texture coordinate).   