Question

I have a small tool that I use to convert some mesh files. The mesh files have the normal’s stored in either DEC3N or UDEC3 format. How do I unpack that to three regular floats cpu side?

Answer 1

It is explained here:
http://www.khronos.org/registry/gles/extensions/OES/OES_vertex_type_10_10_10_2.txt

Modifications to table 2.9 (Component conversions)

    Add the following entries:

        GLType                     Conversion of (x, y, z)  Conversion of w
        -------                    ----------------------   ===============
        INT_10_10_10_2_OES        (2c + 1)/(2^10 - 1)       (2c + 1)/(2^2 - 1)
        UNSIGNED_10_10_10_2_OES    c / (2^10 - 1)            c / (2^2 - 1)

So if you have normal in 32-bit variable N with UDEC3 format, then

x = (float)( (N>>22) / ((1<<10) - 1);
y = (float)( ((N>>12) & ((1<<10)-1)) / ((1<<10) - 1);
z = (float)( ((N>>2)  & ((1<<10)-1)) / ((1<<10) - 1);

Most likely you’ll want to unpack also w, and divide xyz with w.