implement infinite worlds with threaded chunk generation

Sources/Voxelotl/ChunkGeneration.swift

@@ -0,0 +1,92 @@
+import Foundation
+
+public struct ChunkGeneration {
+  private let queue: OperationQueue
+  private let localReadyChunks = ConcurrentDictionary<SIMD3<Int>, Chunk>()
+  private var generatingChunkSet = Set<SIMD3<Int>>()
+
+  weak var world: World?
+
+  init(queue: DispatchQueue) {
+    self.queue = OperationQueue()
+    self.queue.underlyingQueue = queue
+    self.queue.maxConcurrentOperationCount = 8
+    self.queue.qualityOfService = .userInitiated
+  }
+
+  public mutating func generate(chunkID: SIMD3<Int>) {
+    if !generatingChunkSet.insert(chunkID).inserted {
+      return
+    }
+
+    self.queueGenerateJob(chunkID: chunkID)
+  }
+
+  func queueGenerateJob(chunkID: SIMD3<Int>) {
+    self.queue.addOperation {
+      guard let world = self.world else {
+        return
+      }
+      let chunk = world.generateSingleChunkUncommitted(chunkID: chunkID)
+      self.localReadyChunks[chunkID] = chunk
+    }
+  }
+
+  public mutating func generateAdjacentIfNeeded(position: SIMD3<Float>) {
+    guard let world = self.world else {
+      return
+    }
+    let centerChunkID = World.makeID(position: position)
+    for offset in ChunkGeneration.chunkGenerateNeighbors {
+      let chunkID = centerChunkID &+ offset
+      if world.getChunk(id: chunkID) == nil {
+        self.generate(chunkID: chunkID)
+      }
+    }
+  }
+
+  public mutating func acceptReadyChunks() {
+    guard let world = self.world else {
+      return
+    }
+
+    if self.generatingChunkSet.isEmpty {
+      return
+    }
+
+    for (chunkID, chunk) in self.localReadyChunks.take() {
+      world.addChunk(chunkID: chunkID, chunk: chunk)
+      self.generatingChunkSet.remove(chunkID)
+    }
+  }
+
+  private static let chunkGenerateNeighbors: [SIMD3<Int>] = [
+      SIMD3<Int>(-1, -1, -1),
+      SIMD3<Int>(0, -1, -1),
+      SIMD3<Int>(1, -1, -1),
+      SIMD3<Int>(-1, 0, -1),
+      SIMD3<Int>(0, 0, -1),
+      SIMD3<Int>(1, 0, -1),
+      SIMD3<Int>(-1, 1, -1),
+      SIMD3<Int>(0, 1, -1),
+      SIMD3<Int>(1, 1, -1),
+      SIMD3<Int>(-1, -1, 0),
+      SIMD3<Int>(0, -1, 0),
+      SIMD3<Int>(1, -1, 0),
+      SIMD3<Int>(-1, 0, 0),
+      SIMD3<Int>(0, 0, 0),
+      SIMD3<Int>(1, 0, 0),
+      SIMD3<Int>(-1, 1, 0),
+      SIMD3<Int>(0, 1, 0),
+      SIMD3<Int>(1, 1, 0),
+      SIMD3<Int>(-1, -1, 1),
+      SIMD3<Int>(0, -1, 1),
+      SIMD3<Int>(1, -1, 1),
+      SIMD3<Int>(-1, 0, 1),
+      SIMD3<Int>(0, 0, 1),
+      SIMD3<Int>(1, 0, 1),
+      SIMD3<Int>(-1, 1, 1),
+      SIMD3<Int>(0, 1, 1),
+      SIMD3<Int>(1, 1, 1),
+    ]
+}