Hello
The code for computing normals in not accessible from the user in BGRABitmap. Though you can compute it yourself from the height map.
The normal is a 3D vector pointing upwards. From the site you mentioned, I suppose the up way is the z component equal to 1.
To compute the normal vector, you can do the cross product of the slope vector in x and the slope vector in y.
Sx: Slope vector in x
x = 1
y = 0
z = height difference in x = a
Sy: Slope vector in y
x = 0
y = 1
z = height difference in y = b
n: Normal vector:
n = Sx * Sy
x = -a
y = -b
z = 1
The vector is normalized to be of length 1. It is stored as RGB where :
red = x*127 + 128
green = y*127 + 128
blue = z*127 + 128
Regards