From f2b3b078326dcc8af8905909ff941671fb95635c Mon Sep 17 00:00:00 2001
From: Alex Zenla <alex@edera.dev>
Date: Sat, 7 Sep 2024 02:38:54 -0400
Subject: [PATCH] Spatial Chunk Generation

---
 Sources/Voxelotl/ChunkGeneration.swift        | 93 +++++++++++++++++--
 .../Common/ConcurrentDictionary.swift         | 12 +++
 Sources/Voxelotl/Game.swift                   |  2 +-
 Sources/Voxelotl/World.swift                  |  3 +-
 4 files changed, 101 insertions(+), 9 deletions(-)

diff --git a/Sources/Voxelotl/ChunkGeneration.swift b/Sources/Voxelotl/ChunkGeneration.swift
index aa9267a..fb33538 100644
--- a/Sources/Voxelotl/ChunkGeneration.swift
+++ b/Sources/Voxelotl/ChunkGeneration.swift
@@ -1,8 +1,10 @@
 import Foundation
+import Spatial
 
 public struct ChunkGeneration {
   private let queue: OperationQueue
   private let localReadyChunks = ConcurrentDictionary<SIMD3<Int>, Chunk>()
+  private var chunkGenerationOperations = ConcurrentDictionary<SIMD3<Int>, WeakChunkGenerationOperationHolder>()
   private var generatingChunkSet = Set<SIMD3<Int>>()
 
   weak var world: World?
@@ -28,15 +30,54 @@ public struct ChunkGeneration {
   }
 
   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
-    }
+    let operation = ChunkGenerationOperation(chunkID: chunkID)
+    operation.world = self.world
+    operation.localReadyChunks = self.localReadyChunks
+    operation.chunkGenerationOperations = self.chunkGenerationOperations
+    self.queue.addOperation(operation)
+    let holder = WeakChunkGenerationOperationHolder()
+    holder.operation = operation
+    self.chunkGenerationOperations[chunkID] = holder
   }
 
+  public mutating func updatePriorityPosition(position: SIMD3<Float>) {
+    let centerChunkID = World.makeID(position: position)
+    let centerChunkPoint = Point3D(x: Double(centerChunkID.x), y: Double(centerChunkID.y), z: Double(centerChunkID.z))
+
+    self.chunkGenerationOperations.with { operations in
+      var remove: [SIMD3<Int>] = []
+      for (chunkID, operation) in operations {
+        if operation.operation == nil {
+          remove.append(chunkID)
+          continue
+        }
+        let chunkPoint = Point3D(x: Double(chunkID.x), y: Double(chunkID.y), z: Double(chunkID.z))
+        let distance = abs(chunkPoint.distance(to: centerChunkPoint))
+        let priority: Operation.QueuePriority
+        if distance < 3 {
+          priority = .veryHigh
+        } else if distance < 6 {
+          priority = .normal
+        } else if distance < 10 {
+          priority = .low
+        } else {
+          priority = .veryLow
+        }
+
+        if priority == .veryLow {
+          operation.operation?.cancel()
+          self.generatingChunkSet.remove(chunkID)
+        } else {
+          operation.operation?.queuePriority = priority
+        }
+      }
+      
+      for item in remove {
+        operations.removeValue(forKey: item)
+      }
+    }
+  }
+  
   public mutating func generateAdjacentIfNeeded(position: SIMD3<Float>) {
     guard let world = self.world else {
       return
@@ -74,3 +115,41 @@ public struct ChunkGeneration {
     }
   }
 }
+
+class WeakChunkGenerationOperationHolder {
+  weak var operation: ChunkGenerationOperation?
+}
+
+class ChunkGenerationOperation: Operation, @unchecked Sendable {
+  let chunkID: SIMD3<Int>
+
+  weak var world: World?
+  weak var localReadyChunks: ConcurrentDictionary<SIMD3<Int>, Chunk>?
+  weak var chunkGenerationOperations: ConcurrentDictionary<SIMD3<Int>, WeakChunkGenerationOperationHolder>?
+
+  init(chunkID: SIMD3<Int>) {
+    self.chunkID = chunkID
+  }
+
+  override func main() {
+    if isCancelled {
+      return
+    }
+    
+    guard let world = self.world else {
+      return
+    }
+
+    guard let localReadyChunks = self.localReadyChunks else {
+      return
+    }
+
+    let chunk = world.generateSingleChunkUncommitted(chunkID: self.chunkID)
+    localReadyChunks[chunkID] = chunk
+    
+    guard let chunkGenerationOperations = self.chunkGenerationOperations else {
+      return
+    }
+    chunkGenerationOperations.remove(key: chunkID)
+  }
+}
diff --git a/Sources/Voxelotl/Common/ConcurrentDictionary.swift b/Sources/Voxelotl/Common/ConcurrentDictionary.swift
index 7bf480a..c333699 100644
--- a/Sources/Voxelotl/Common/ConcurrentDictionary.swift
+++ b/Sources/Voxelotl/Common/ConcurrentDictionary.swift
@@ -75,6 +75,18 @@ public class ConcurrentDictionary<V: Hashable, T>: Collection {
       self.inner.removeAll(keepingCapacity: keep)
     }
   }
+  
+  @discardableResult public func remove(key: V) -> T? {
+    self.locked {
+      self.inner.removeValue(forKey: key)
+    }
+  }
+  
+  public func with(_ perform: (inout [V : T]) -> Void) {
+    self.locked {
+      perform(&self.inner)
+    }
+  }
 
   fileprivate func locked<X>(_ perform: () -> X) -> X {
     self.lock.lock()
diff --git a/Sources/Voxelotl/Game.swift b/Sources/Voxelotl/Game.swift
index 6b56126..3fa0923 100644
--- a/Sources/Voxelotl/Game.swift
+++ b/Sources/Voxelotl/Game.swift
@@ -83,7 +83,7 @@ class Game: GameDelegate {
     }
 
     self.world.generateAdjacentChunksIfNeeded(position: self.player.position)
-    self.world.update()
+    self.world.update(priorityPosition: self.player.position)
   }
 
   public static let material = Material(
diff --git a/Sources/Voxelotl/World.swift b/Sources/Voxelotl/World.swift
index 214154c..a3b69fa 100644
--- a/Sources/Voxelotl/World.swift
+++ b/Sources/Voxelotl/World.swift
@@ -107,7 +107,8 @@ public class World {
     }
   }
 
-  public func update() {
+  public func update(priorityPosition: SIMD3<Float>) {
+    self._chunkGeneration.updatePriorityPosition(position: priorityPosition)
     self._chunkGeneration.acceptReadyChunks()
   }