Calculate flow, and if it ends in a sink, it cuts the lowest neighboring tile that is also in a different direction, to just below the current elevation. This should, in theory, create canyons through some highlands.
There are many questions, such as: is there a limit to how much it will cut so we can still get Death Valleys and Caspian Seas? If it hits that limit, how do we backtrack and warn the algorithm not to try again? What happens if the cut just leads to another sink?
What if the limit is at most one tile? Might not have to backtrack that way.
Would it help to use steepness of the neighbor, instead of elevation, as with the erosion terrain task?
What if the shore-distance is used as one tie-breaker (probably not the only) for similar elevation choices? With the goal of the river to travel closer to the ocean if given a choice.
Alternatively, this might just be an option on the flow algorithm, so the tiles retain their elevations but the rivers are marked as going through canyons. Canyons are often too narrow to appear on some scales of maps.
Calculate flow, and if it ends in a sink, it cuts the lowest neighboring tile that is also in a different direction, to just below the current elevation. This should, in theory, create canyons through some highlands.
There are many questions, such as: is there a limit to how much it will cut so we can still get Death Valleys and Caspian Seas? If it hits that limit, how do we backtrack and warn the algorithm not to try again? What happens if the cut just leads to another sink?
What if the limit is at most one tile? Might not have to backtrack that way.
Would it help to use steepness of the neighbor, instead of elevation, as with the erosion terrain task?
What if the shore-distance is used as one tie-breaker (probably not the only) for similar elevation choices? With the goal of the river to travel closer to the ocean if given a choice.
Alternatively, this might just be an option on the flow algorithm, so the tiles retain their elevations but the rivers are marked as going through canyons. Canyons are often too narrow to appear on some scales of maps.