Added a river coordinate system - it's just far enough from the tile oordinate system to be incredibly annoying

core/src/com/unciv/logic/map/MapGenerator.kt

@@ -741,3 +741,28 @@ class MapGenerator(val ruleset: Ruleset) {
         // endregion
     }
 }
+
+class RiverGenerator(){
+
+    public class RiverCoordinate(val position: Vector2, val bottomRightOrLeft:BottomRightOrLeft){
+        enum class BottomRightOrLeft{
+            BottomLeft, BottomRight
+        }
+
+        fun getAdjacentPositions(): Sequence<RiverCoordinate> {
+            // What's nice is that adjacents are always the OPPOSITE in terms of right-left - rights are adjacent to only lefts, and vice-versa
+            // This means that a lot of obviously-wrong assignments are simple to spot
+            if (bottomRightOrLeft == BottomRightOrLeft.BottomLeft) {
+                return sequenceOf(RiverCoordinate(position, BottomRightOrLeft.BottomRight), // same tile, other side
+                        RiverCoordinate(position.cpy().add(1f,0f), BottomRightOrLeft.BottomRight), // tile to MY top-left, take its bottom right corner
+                        RiverCoordinate(position.cpy().add(0f,-1f), BottomRightOrLeft.BottomRight) // Tile to MY bottom-left, take its bottom right
+                )
+            } else {
+                return sequenceOf(RiverCoordinate(position, BottomRightOrLeft.BottomLeft), // same tile, other side
+                        RiverCoordinate(position.cpy().add(0f,1f), BottomRightOrLeft.BottomLeft), // tile to MY top-right, take its bottom left
+                        RiverCoordinate(position.cpy().add(-1f,0f), BottomRightOrLeft.BottomLeft)  // tile to MY bottom-right, take its bottom left
+                )
+            }
+        }
+    }
+}