  Massive giant planets, such as the ones being discovered by direct imaging
surveys, likely experience the majority of their growth through a
circumplanetary disc. We argue that the entropy of accreted material is
determined by boundary layer processes, unlike the "cold-" or "hot-start"
hypotheses usually invoked in the core accretion and direct collapse scenarios.
A simple planetary evolution model illustrates how a wide range of radius and
luminosity tracks become possible, depending on details of the accretion
process. Specifically, the proto-planet evolves towards "hot-start" tracks if
the scale-height of the boundary layer is $\gtrsim0.24$, a value not much
larger than the scale-height of the circumplanetary disc. Understanding the
luminosity and radii of young giant planets will thus require detailed models
of circumplanetary accretion.
