  We introduce the tropical $F$-polynomial $f_M$ of a quiver representation
$M$. We study its interplay with the general presentation for any
finite-dimensional basic algebra. We give an interpretation of evaluating $f_M$
at a weight vector. As a consequence, we give a presentation of the Newton
polytope ${\sf N}(M)$ of $M$. We study the dual fan and 1-skeleton of ${\sf
N}(M)$. We propose an algorithm to determine the generic Newton polytopes, and
show it works for path algebras. As an application, we give a
representation-theoretic interpretation of Fock-Goncharov's duality pairing. We
give an explicit construction of dual clusters, which consists of real Schur
representations. We specialize the above general results to the cluster-finite
algebras and the preprojective algebras of Dynkin type.
