  We present the {\sc warpfield} emission predictor, {\sc warpfield-emp}, which
couples the 1D stellar feedback code {\sc warpfield} with the {\sc cloudy} \hii
region/PDR code and the {\sc polaris} radiative transfer code, in order to make
detailed predictions for the time-dependent line and continuum emission arising
from the H{\sc ii} region and PDR surrounding an evolving star cluster. {\sc
warpfield-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 broad
ranges of different cloud parameters. We compare the results of an extensive
set of models with SITELLE observations of a large sample of \hii regions in
NGC~628 and find very good agreement, particularly for the highest
signal-to-noise observations. We show that our approach of modeling individual
clouds from first principles (instead of in terms of dimensionless quantities
such as the ionization parameter) allows us to avoid long-standing degeneracies
in the interpretation of \hii region diagnostics and enables us to relate these
diagnostics to important physical parameters such as cloud mass or cluster age.
Finally, we explore the implications of our models regarding the reliability of
simple metallicity diagnostics, the properties of long-lived embedded clusters,
and the role played by winds and supernovae in regulating \hii region and PDR
line emission.
