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I have an engine which generates random Islands. At the moment it tends to generate quite a lot of lagoons and lakes. I would like to know of a feasible way of detecting them so that I can mark them as different terrain (i.e., salt water for lagoons).

Note: lagoons must be treated differently than lakes. I don't know what the threshhold for a lake should be, but obviously bodies of water close to the coast should be marked as salt water so the player is affected properly when trying to drink the water.

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    \$\begingroup\$ How is the terrain represented? What kind of generation data you have access to? \$\endgroup\$
    – wondra
    Aug 30 '14 at 10:55
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I think the easiest way to do this is with a flood-fill algorithm.

  • Pick a square that you know is water, and not a lagoon (eg. top-left corner's water tile)
  • Flood fill, marking any water tile with a flag
  • Mark any water tiles left that don't have the flag as lakes/lagoons.

I assume you know what flood fill is (looking at all adjacent tiles recursively until you run out of tiles).

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    \$\begingroup\$ So... that is BFS, right? \$\endgroup\$
    – wondra
    Aug 30 '14 at 11:49
  • \$\begingroup\$ I'll try some different methods to see if I can get the behavior I want. I need to mark lagoons as salt water, and lakes as fresh water. \$\endgroup\$
    – Truncheon
    Aug 30 '14 at 17:39
  • \$\begingroup\$ @Truncheon I think you're confused. How do you know, simply from the data, what's a lake and what's a lagoon? What are the discriminating criteria? If you can't tell, you are stuck. \$\endgroup\$
    – ashes999
    Aug 30 '14 at 19:18
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    \$\begingroup\$ @wondra not necessarily. Both breadth-first and depth-first search can be applied equally to flood-fill algorithms. \$\endgroup\$
    – ashes999
    Aug 30 '14 at 19:18
  • \$\begingroup\$ An arbitrary value will have to be set of course; if part of the water body is within a certain distance of the coast then it's marked as a logoon, otherwise it's a lake. Jus wanted to know the most efficient way of doing this; the way I have in my mind already would be very slow. \$\endgroup\$
    – Truncheon
    Aug 31 '14 at 9:36
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There is always brute force solution if you find yourself stuck and speed is not priority (one-time generation).
In you case simple BFS/DFS might suffice. Just pick a node of desired type(either land of water) and continue your search, finding all tiles of same type within the graph(terrain part). Continue while there are any nodes not visited.

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