We present the {\sc warpfield} emission predictor, {\sc warpfield-emp}, whichcouples the 1D stellar feedback code {\sc warpfield} with the {\sc cloudy} \hiiregion/PDR code and the {\sc polaris} radiative transfer code, in order to makedetailed predictions for the time-dependent line and continuum emission arisingfrom the H{\sc ii} region and PDR surrounding an evolving star cluster. {\scwarpfield-emp} accounts for a wide range of physical processes (stellar winds,supernovae, radiation pressure, gravity, thermal conduction, radiative cooling,dust extinction etc.) and yet runs quickly enough to allow us to explore broadranges of different cloud parameters. We compare the results of an extensiveset of models with SITELLE observations of a large sample of \hii regions inNGC~628 and find very good agreement, particularly for the highestsignal-to-noise observations. We show that our approach of modeling individualclouds from first principles (instead of in terms of dimensionless quantitiessuch as the ionization parameter) allows us to avoid long-standing degeneraciesin the interpretation of \hii region diagnostics and enables us to relate thesediagnostics to important physical parameters such as cloud mass or cluster age.Finally, we explore the implications of our models regarding the reliability ofsimple metallicity diagnostics, the properties of long-lived embedded clusters,and the role played by winds and supernovae in regulating \hii region and PDRline emission.