This asset provides you with a simple method to flood-fill areas of an image. However this is NOT a typical flood-fill algorithm, and instead uses a very simple shader and a coloured base image to create the flood-fill effect (hence the name "lazy" fill!).
The asset is based on "map" sprites and "outline" sprites, where the map sprite defines the areas that can be filled in, and the outline sprite is an overlay used to show the outlines of the coloured areas. Then a shader does all the rest. The asset also includes an FXAA shader that is used to smooth the edges of the final result.