  We present a method, based on the positive weight next-to-leading-order
matching formalism (POWHEG), to simulate photon production processes at
next-to-leading-order (NLO). This technique is applied to the simulation of
diphoton production in hadron-hadron collisions. The algorithm consistently
combines the parton shower and NLO calculation, producing only positive weight
events. The simulation includes both the photon fragmentation contribution and
a full implementation of the truncated shower required to correctly describe
soft emissions in an angular-ordered parton shower.
