HP b2600 Supplementary Manual page 62

programming hints
OpenGL performance hints
60
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 computed as follows:
Let m denote the matrix element in row i and column j of M
ij
numbering the topmost row of the matrix as row 1, and the left most
column as column 1. Then
Alternatively, an implementation may chose to normalize the normal
instead of rescaling the normal. Then
If normalization is disabled, then the square root in equation 2.1 is
replaced with 1; otherwise, it is calculated as dictated by the OpenGL
Spec. If both normalize and rescale are enabled, HP's implementation
skips the rescale and does only the normalize.
-1
,
Chapter 5