Indeed light simply just uses a Dijkstra-like flood [1] fill :) This isotropic propagation is the reason Fermat's principle [2] works. [1] The flood pattern,

Indeed light simply just uses a Dijkstra-like flood [1] fill :) This isotropic propagation is the reason Fermat's principle [2] works. [1] The flood pattern, or Huygens principle, in turns follow from the local (fundamental) and isotropic (for most media) nature of Maxwell's equations for electromagnetic propagation. [2] https://en.wikipedia.org/wiki/Fermat's_principle https://en.wikipedia.org/wiki/Fermat's_principle