OpenGL Implementation Guide for HP-UX 11.x
Page 62
... Alternatively, an implementation may chose to normalize the normal instead of the matrix as row 1, and the left most column as dictated by the OpenGL Spec. programming hints OpenGL performance hints Therefore, if the modelview matrix is M, the transformed plane equation is: the rescaled normal is and the fully transformed normal... is If rescaling is disabled, f is 1, otherwise f is replaced with 1; otherwise, it is calculated as column 1. If both normalize and rescale are enabled, HP's implementation skips the rescale and does only the normalize. 60 Chapter 5
... Alternatively, an implementation may chose to normalize the normal instead of the matrix as row 1, and the left most column as dictated by the OpenGL Spec. programming hints OpenGL performance hints Therefore, if the modelview matrix is M, the transformed plane equation is: the rescaled normal is and the fully transformed normal... is If rescaling is disabled, f is 1, otherwise f is replaced with 1; otherwise, it is calculated as column 1. If both normalize and rescale are enabled, HP's implementation skips the rescale and does only the normalize. 60 Chapter 5