Tilesets: Added edge tile images!

core/src/com/unciv/logic/map/tile/Tile.kt

@@ -691,6 +691,8 @@ class Tile : IsPartOfGameInfoSerialization, Json.Serializable {
         else probability
     }
     
+    fun isTilemapInitialized() = ::tileMap.isInitialized
+
     //endregion
     //region state-changing functions
 
@@ -712,7 +714,7 @@ class Tile : IsPartOfGameInfoSerialization, Json.Serializable {
         isOcean = baseTerrain == Constants.ocean
 
         // Resource amounts missing - Old save or bad mapgen?
-        if (::tileMap.isInitialized && resource != null && tileResource.resourceType == ResourceType.Strategic && resourceAmount == 0) {
+        if (isTilemapInitialized() && resource != null && tileResource.resourceType == ResourceType.Strategic && resourceAmount == 0) {
             // Let's assume it's a small deposit
             setTileResource(tileResource, majorDeposit = false)
         }
@@ -812,7 +814,7 @@ class Tile : IsPartOfGameInfoSerialization, Json.Serializable {
     }
 
     private fun updateUniqueMap() {
-        if (!::tileMap.isInitialized) return // This tile is a fake tile, for visual display only (e.g. map editor, civilopedia)
+        if (!isTilemapInitialized()) return // This tile is a fake tile, for visual display only (e.g. map editor, civilopedia)
         val terrainNameList = allTerrains.map { it.name }.toList()
 
         // List hash is function of all its items, so the same items in the same order will always give the same hash

core/src/com/unciv/ui/components/tilegroups/TileSetStrings.kt

@@ -8,6 +8,8 @@ import com.unciv.models.metadata.GameSettings
 import com.unciv.models.ruleset.Ruleset
 import com.unciv.models.tilesets.TileSetCache
 import com.unciv.models.tilesets.TileSetConfig
+import com.unciv.ui.components.tilegroups.layers.EdgeTileImage
+import com.unciv.ui.components.tilegroups.layers.NeighborDirection
 import com.unciv.ui.images.ImageAttempter
 import com.unciv.ui.images.ImageGetter
 
@@ -67,6 +69,26 @@ class TileSetStrings(
     val bottomRiver by lazy { orFallback { tilesLocation + "River-Bottom"} }
     val bottomLeftRiver  by lazy { orFallback { tilesLocation + "River-BottomLeft"} }
     
+    val edgeImagesByPosition = ImageGetter.getAllImageNames()
+        .filter { it.startsWith(tileSetLocation +"Edges/") }
+        .mapNotNull {
+            val split = it.split('/').last() // without folder
+                .split("-")
+            // Comprised of 3 parts: origin tilefilter, destination tilefilter, 
+            //   and edge type: Bottom, BottomLeft or BottomRight
+            if (split.size != 4) return@mapNotNull null
+
+            // split[0] is name and is unused
+            val originTileFilter = split[1]
+            val destinationTileFilter = split[2]
+            val neighborDirection = split[3]
+            val neighborDirectionEnumValue = NeighborDirection.entries
+                .firstOrNull { it.name == neighborDirection } ?: return@mapNotNull null
+
+            EdgeTileImage(it, originTileFilter, destinationTileFilter, neighborDirectionEnumValue)
+        }
+        .groupBy { it.edgeType }
+
     val unitsLocation = unitSetLocation + "Units/"
 
     val bordersLocation = tileSetLocation + "Borders/"

core/src/com/unciv/ui/components/tilegroups/layers/TileLayerTerrain.kt

@@ -1,6 +1,7 @@
 package com.unciv.ui.components.tilegroups.layers
 
 import com.badlogic.gdx.graphics.Color
+import com.badlogic.gdx.math.Vector2
 import com.badlogic.gdx.scenes.scene2d.Actor
 import com.badlogic.gdx.scenes.scene2d.ui.Image
 import com.unciv.UncivGame
@@ -86,8 +87,30 @@ class TileLayerTerrain(tileGroup: TileGroup, size: Float) : TileLayer(tileGroup,
         }
     }
     
+    private fun getEdgeTileLocations(): Sequence<String> {
+        val tile = tile()
+        if (!tile.isTilemapInitialized()) // fake tile 
+            return emptySequence()
+        return tile.neighbors
+            .filter { it.position.x < tile.position.x || it.position.y < tile.position.y }
+            .flatMap { getMatchingEdges(tile, it) }
+    }
+
+    private fun getMatchingEdges(originTile: Tile, neighborTile: Tile): List<String>{
+        val vectorToNeighbor =  neighborTile.position.cpy().sub(originTile.position)
+        val direction = NeighborDirection.fromVector(vectorToNeighbor) ?: return emptyList()
+        val possibleEdgeFiles = strings().edgeImagesByPosition[direction] ?: return emptyList()
+
+        return possibleEdgeFiles.filter {
+            if (!originTile.matchesFilter(it.originTileFilter)) return@filter false
+            if (!neighborTile.matchesFilter(it.destinationTileFilter)) return@filter false
+            return@filter true
+        }.map { it.fileName }
+    }
+
     private fun updateTileImage(viewingCiv: Civilization?) {
-        val tileBaseImageLocations = getTileBaseImageLocations(viewingCiv)
+        val tileBaseImageLocations = getTileBaseImageLocations(viewingCiv) + 
+                getEdgeTileLocations()
         
         if (tileBaseImageLocations.size == tileImageIdentifiers.size) {
             if (tileBaseImageLocations.withIndex().all { (i, imageLocation) -> tileImageIdentifiers[i] == imageLocation })
@@ -211,3 +234,21 @@ class TileLayerTerrain(tileGroup: TileGroup, size: Float) : TileLayer(tileGroup,
             else baseHexagon + strings().orFallback{ getTile(tileGroup.tile.naturalWonder!!) }
 
 }
+
+enum class NeighborDirection {
+    Top, TopRight, TopLeft, Bottom, BottomLeft, BottomRight;
+
+    companion object {
+        fun fromVector(vector2: Vector2): NeighborDirection? = when {
+            vector2.x == 1f && vector2.y == 1f -> Top
+            vector2.x == 0f && vector2.y == 1f -> TopRight
+            vector2.x == 1f && vector2.y == 0f -> TopLeft
+            vector2.x == -1f && vector2.y == -1f -> Bottom
+            vector2.x == 0f && vector2.y == -1f -> BottomLeft
+            vector2.x == -1f && vector2.y == 0f -> BottomRight
+            else -> null
+        }
+    }
+}
+
+data class EdgeTileImage(val fileName:String, val originTileFilter: String, val destinationTileFilter: String, val edgeType: NeighborDirection)

core/src/com/unciv/ui/images/ImageGetter.kt

@@ -468,6 +468,8 @@ object ImageGetter {
         return specialist
     }
     
+    fun getAllImageNames() = textureRegionDrawables.keys
+
     fun getAvailableSkins() = ninePatchDrawables.keys.asSequence().map { it.split("/")[1] }.distinct()
 
     /** Determines available TileSets from the currently loaded Texture paths.

docs/Modders/Creating-a-custom-tileset.md

@@ -146,3 +146,22 @@ They can be for unit types (Archery, Seige, Cavalry) or for specific unit names
 
 The files should be in the format of `<unit type/unit name>-attack-<frame number>`.
 For example, a 3 frame animation for Sword units would have the files `Sword-attack-1.png`, `Sword-attack-3.png`, `Sword-attack-3.png`
+
+## Edge images
+
+You can add additional images that will be drawn only when a tile is adjacent to another tile in a specific direction.
+
+The images should be placed in the `Images/Tilesets/<tileset name>/Edges` folder, rather than in `/Tiles`.
+
+The name of the tile should be `<tile name>-<origin tile filter>-<destination tile filter>-<neighbor direction>.png`, where direction of one of:
+
+- Bottom
+- BottomLeft
+- BottomRight
+- Top
+- TopLeft
+- TopRight
+
+For example: `Cliff-Hills-Coast-Top.png`
+
+The initial name has no bearing on the image used, it is just a way to group images together.