impl sinkholes

island/generators.ts

@@ -168,6 +168,50 @@ export const NO_ISLAND: LobeGeneratorConstructor =
     return true;
   };
 
+const SINKHOLE_BURNOUT = 1500;
+
+/** carve out elevation */
+export const SINKHOLE: LobeGeneratorConstructor = (
+  islands: IslandGrid,
+  basePos: number
+) => {
+  // emergency cutoff in case sinkhole ends up fighting a generator that terminates at a given elevation
+  let ticks = 0;
+  return () => {
+    if (ticks++ < SINKHOLE_BURNOUT) {
+      const sunk = islands.floodSearch(basePos, (tile) => tile < 0);
+
+      islands.sinkhole(islands.choose(sunk));
+    }
+
+    return true;
+  };
+};
+
+/** carve out elevation more aggressively */
+export const WIDE_SINKHOLE: LobeGeneratorConstructor = (
+  islands: IslandGrid,
+  basePos: number
+) => {
+  // emergency cutoff in case sinkhole ends up fighting a generator that terminates at a given elevation
+  let ticks = 0;
+  return () => {
+    if (ticks++ < SINKHOLE_BURNOUT) {
+      const sunk = islands.floodSearch(basePos, (tile) => tile < 0);
+
+      const sunkEdge = sunk.filter((pos) => islands.data[pos] >= WATER);
+
+      if (sunkEdge.length > 0) {
+        islands.sinkhole(islands.choose(sunkEdge));
+      } else {
+        islands.sinkhole(islands.choose(sunk));
+      }
+    }
+
+    return true;
+  };
+};
+
 export const BIG_ISLANDS = [BIG_MOUNTAIN, BIG_BEACH, HILLY_FOREST];
 export const ROCKY_ISLANDS = [SMALL_MOUNTAIN, BIG_MOUNTAIN, HILLY_FOREST];
 export const GREEN_ISLANDS = [
@@ -186,3 +230,4 @@ export const ALL_ISLANDS = [
   HILLY_FOREST,
   ERODED_BEACH,
 ];
+export const VOIDS = [NO_ISLAND, SINKHOLE, WIDE_SINKHOLE];

island/grid.ts

@@ -7,7 +7,9 @@ import {
   LobeGenerator,
   NO_ISLAND,
   ROCKY_ISLANDS,
+  SINKHOLE,
   SMALL_ISLANDS,
+  VOIDS,
 } from "./generators";
 
 export class IslandGrid {
@@ -30,10 +32,10 @@ export class IslandGrid {
       this.choose(SMALL_ISLANDS),
       this.choose(ALL_ISLANDS),
       this.choose(ALL_ISLANDS),
-      NO_ISLAND,
-      NO_ISLAND,
-      NO_ISLAND,
-      NO_ISLAND,
+      this.choose(VOIDS),
+      this.choose(VOIDS),
+      this.choose(VOIDS),
+      this.choose(VOIDS),
       NO_ISLAND,
       NO_ISLAND,
     ]);
@@ -126,10 +128,36 @@ export class IslandGrid {
     }
 
     // flat, increase elevation
-    const newValue = ++this.data[pos];
-    if (newValue == ICECAP) {
-      this.done = true;
+    ++this.data[pos];
+  }
+
+  public sinkhole(pos: number): void {
+    const higherNeighbors: number[] = [];
+
+    const check = (adjPos: number) => {
+      if (this.data[adjPos] > this.data[pos]) {
+        higherNeighbors.push(adjPos);
+      }
+    };
+
+    // try to pull from neighbors
+
+    check((pos - this.width - 1) % this.data.length);
+    check((pos - this.width) % this.data.length);
+    check((pos - this.width + 1) % this.data.length);
+    check((pos - 1) % this.data.length);
+    check((pos + 1) % this.data.length);
+    check((pos + this.width - 1) % this.data.length);
+    check((pos + this.width) % this.data.length);
+    check((pos + this.width + 1) % this.data.length);
+
+    if (higherNeighbors.length > 0) {
+      const uphill = higherNeighbors[this.rng() % higherNeighbors.length];
+      return this.sinkhole(uphill);
     }
+
+    // flat, decrease elevation
+    this.data[pos] = Math.max(this.data[pos] - 1, -3);
   }
 
   public choose<T>(list: T[]) {

island/render.ts

@@ -9,6 +9,11 @@ export function renderIslands(
     for (let x = 0; x < islands.width; x++) {
       const tile = islands.data[islands.xy(x, y)];
       switch (tile) {
+        case -3:
+        case -2:
+        case -1:
+          cx.fillStyle = "#000088";
+          break;
         case WATER:
           cx.fillStyle = "blue";
           break;