From cb2ffe78a4a189aa7605b03cbf2c8b80979291d1 Mon Sep 17 00:00:00 2001
From: a dinosaur <dino@a-dinosaur.com>
Date: Thu, 22 Aug 2024 03:37:29 +1000
Subject: [PATCH] use arc4random to seed non-csprng, fleshes out random
 subsystem

---
 Sources/Voxelotl/CMakeLists.txt            |  2 ++
 Sources/Voxelotl/Game.swift                | 31 ++++++++++++--------
 Sources/Voxelotl/Random/Arc4Random.swift   | 10 +++++--
 Sources/Voxelotl/Random/DarwinRandom.swift | 33 ++++++++++++++++++++++
 Sources/Voxelotl/Random/RandomRange.swift  | 20 +++++++++++++
 Sources/Voxelotl/Renderer.swift            |  2 +-
 6 files changed, 83 insertions(+), 15 deletions(-)
 create mode 100644 Sources/Voxelotl/Random/DarwinRandom.swift
 create mode 100644 Sources/Voxelotl/Random/RandomRange.swift

diff --git a/Sources/Voxelotl/CMakeLists.txt b/Sources/Voxelotl/CMakeLists.txt
index 3a129e7..3b762de 100644
--- a/Sources/Voxelotl/CMakeLists.txt
+++ b/Sources/Voxelotl/CMakeLists.txt
@@ -13,7 +13,9 @@ add_executable(Voxelotl MACOSX_BUNDLE
   Color.swift
 
   Random/RandomProvider.swift
+  Random/RandomRange.swift
   Random/Arc4Random.swift
+  Random/DarwinRandom.swift
 
   NSImageLoader.swift
   Renderer.swift
diff --git a/Sources/Voxelotl/Game.swift b/Sources/Voxelotl/Game.swift
index 174c132..113e010 100644
--- a/Sources/Voxelotl/Game.swift
+++ b/Sources/Voxelotl/Game.swift
@@ -25,18 +25,21 @@ class Game: GameDelegate {
   var player = Player()
   var projection: matrix_float4x4 = .identity
   var chunk = Chunk(position: .zero)
-  var random = Arc4Random.instance
 
   init() {
-    player.position = SIMD3(0.5, Float(Chunk.chunkSize) + 0.5, 0.5)
-    player.rotation = .init(.pi, 0)
+    self.player.position = SIMD3(0.5, Float(Chunk.chunkSize) + 0.5, 0.5)
+    self.player.rotation = .init(.pi, 0)
+    self.generateWorld()
+  }
 
+  private func generateWorld() {
+    var random = DarwinRandom(seed: Arc4Random.instance.next(in: DarwinRandom.max))
     let colors: [Color<UInt8>] = [
       .white,
       .red, .blue, .green,
       .magenta, .yellow, .cyan
     ]
-    chunk.fill(allBy: {
+    self.chunk.fill(allBy: {
       if (random.next() & 0x1) == 0x1 {
         .solid(colors[random.next(in: 0..<colors.count)])
       } else {
@@ -59,19 +62,25 @@ class Game: GameDelegate {
     if let pad = GameController.current?.state {
       // Delete block underneath player
       if pad.pressed(.south) {
-        chunk.setBlock(at: SIMD3(player.position + .down * 0.2), type: .air)
+        self.chunk.setBlock(at: SIMD3(player.position + .down * 0.2), type: .air)
       }
+
       // Player reset
       if pad.pressed(.back) {
-        player.position = .init(repeating: 0.5) + .init(0, Float(Chunk.chunkSize), 0)
-        player.velocity = .zero
-        player.rotation = .init(.pi, 0)
+        self.player.position = .init(repeating: 0.5) + .init(0, Float(Chunk.chunkSize), 0)
+        self.player.velocity = .zero
+        self.player.rotation = .init(.pi, 0)
+      }
+
+      // Regenerate
+      if pad.pressed(.start) {
+        self.generateWorld()
       }
     }
 
-    player.update(deltaTime: deltaTime, chunk: chunk)
-    camera.position = player.eyePosition
-    camera.rotation = player.eyeRotation
+    self.player.update(deltaTime: deltaTime, chunk: chunk)
+    self.camera.position = player.eyePosition
+    self.camera.rotation = player.eyeRotation
   }
 
   func draw(_ renderer: Renderer, _ time: GameTime) {
diff --git a/Sources/Voxelotl/Random/Arc4Random.swift b/Sources/Voxelotl/Random/Arc4Random.swift
index d0a17bd..2d3a75b 100644
--- a/Sources/Voxelotl/Random/Arc4Random.swift
+++ b/Sources/Voxelotl/Random/Arc4Random.swift
@@ -17,8 +17,12 @@ public class Arc4Random: RandomProvider {
     arc4random()
   }
 
-  public func next(in bound: Range<Int>) -> Int {
-    assert(bound.upperBound <= Self.max)
-    return bound.lowerBound + Int(arc4random_uniform(UInt32(bound.upperBound)))
+  public func next(in bound: Int) -> Int {
+    assert(bound <= Self.max)
+    return Int(arc4random_uniform(UInt32(bound)))
+  }
+
+  public func next(in range: Range<Int>) -> Int {
+    return range.lowerBound + next(in: range.upperBound - range.lowerBound)
   }
 }
diff --git a/Sources/Voxelotl/Random/DarwinRandom.swift b/Sources/Voxelotl/Random/DarwinRandom.swift
new file mode 100644
index 0000000..daf30a3
--- /dev/null
+++ b/Sources/Voxelotl/Random/DarwinRandom.swift
@@ -0,0 +1,33 @@
+public struct DarwinRandom: RandomProvider {
+  public typealias Output = Int
+
+  public static var min: Int { 0x00000000 }
+  public static var max: Int { 0x7FFFFFFF }
+
+  private var state: Int
+
+  init() {
+    self.state = 0
+  }
+
+  public init(seed: Int) {
+    self.state = seed
+  }
+
+  mutating public func seed(with seed: Int) {
+    self.state = seed
+  }
+
+  mutating public func next() -> Int {
+    if self.state == 0 {
+      self.state = 123459876
+    }
+    let hi = self.state / 127773
+    let lo = self.state - hi * 127773
+    self.state = 16807 * lo - 2836 * hi
+    if self.state < 0 {
+      self.state += Self.max
+    }
+    return self.state % (Self.max + 1)
+  }
+}
diff --git a/Sources/Voxelotl/Random/RandomRange.swift b/Sources/Voxelotl/Random/RandomRange.swift
new file mode 100644
index 0000000..baf5b61
--- /dev/null
+++ b/Sources/Voxelotl/Random/RandomRange.swift
@@ -0,0 +1,20 @@
+public extension RandomProvider where Output: BinaryInteger {
+  mutating func next(in range: Range<Int>) -> Int {
+    range.lowerBound + self.next(in: range.upperBound - range.lowerBound)
+  }
+
+  mutating func next(in range: ClosedRange<Int>) -> Int {
+    range.lowerBound + self.next(in: range.upperBound - range.lowerBound + 1)
+  }
+
+  mutating func next(in bound: Int) -> Int {
+    assert(Self.min == 0)
+    assert(Self.max >= bound)
+    let threshold = Int(Self.max % Output(bound))
+    var result: Int
+    repeat {
+      result = Int(truncatingIfNeeded: self.next())
+    } while result < threshold
+    return result % bound
+  }
+}
diff --git a/Sources/Voxelotl/Renderer.swift b/Sources/Voxelotl/Renderer.swift
index c5d55b1..7473381 100644
--- a/Sources/Voxelotl/Renderer.swift
+++ b/Sources/Voxelotl/Renderer.swift
@@ -358,7 +358,7 @@ public class Renderer {
     let instancesBytes = numInstances * MemoryLayout<VertexShaderInstance>.stride
 
     // (Re)create instance buffer if needed
-    if self._instances[self.currentFrame] == nil || numInstances > self._instances[self.currentFrame]!.length {
+    if self._instances[self.currentFrame] == nil || instancesBytes > self._instances[self.currentFrame]!.length {
       guard let instanceBuffer = self.device.makeBuffer(
         length: instancesBytes,
         options: .storageModeManaged)