> How much more complicated would it be if the obstacles were not polygons but points on a grid? I think with grids, one approach would be to go with a flood f

> How much more complicated would it be if the obstacles were not polygons but points on a grid? I think with grids, one approach would be to go with a flood fill kind of an algorithm, but doing it cell-by-cell will be costly. An alternative way would be to unify cells together as a polygon and do intersection testing; with a hammer everything looks like a nail :P I think in games like Baldur's Gate, [Portal Visibility](http://playtechs.blogspot.in/2007/03/2d-portal-visibility-part-1.html http://playtechs.blogspot.in/2007/03/2d-portal-visibility-pa...) is commonly used.