I try to inverse x axis of my model by calling scalef(-1.0f,1.0f,1.0f);
the vertex position turn out right but the lighting is incorrect.
when light is on the left side of the x-inverse model the right side of the model become lit.
In my shader I already Multiply gl_Normal with gl_NormalMatrix before lighting calculation.
Please help me this is the first time I encouter this problem (never use scaling before )