the sample "fluidGL" in SDK

I ran the sample “fluidGL” in SDK, it turned out the problem:

[root@localhost fluidsGL]# make
/usr/bin/ld: cannot find -lXi
collect2: ld return 1
make: *** […/…/bin/linux/release/fluidsGL] error 1

…What’s -lXi? Some lib from X window? How can I find it?
Thanks!