From fdcf62db74da721e84145ce7206d0eaa9b75a6a8 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 6 Aug 2017 08:25:13 -0700
Subject: [PATCH] [MetaballsKit] Just replace balls when size changes

---
 MetaballsKit/Metaballs.swift | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/MetaballsKit/Metaballs.swift b/MetaballsKit/Metaballs.swift
index a4e201d..84b15a9 100644
--- a/MetaballsKit/Metaballs.swift
+++ b/MetaballsKit/Metaballs.swift
@@ -43,7 +43,16 @@ public class Field {
                 let numberOfBallsBeforeFilter = balls.count
 
                 // Remove balls that fall outside the new bounds.
-                balls = balls.filter { bounds.contains($0.bounds) }
+//                balls = balls.filter { bounds.contains($0.bounds) }
+
+                // Scale balls to new position and size.
+                let scale = Float(size.width / oldValue.width)
+                balls = balls.map {
+                    let r = $0.radius * scale
+                    let p = randomPoint(forBallWithRadius: r)
+                    let v = Vector(dx: $0.velocity.dx * scale, dy: $0.velocity.dy * scale)
+                    return Ball(radius: r, position: p, velocity: v)
+                }
 
                 // Update Metal state as needed.
                 populateParametersBuffer()
@@ -91,11 +100,7 @@ public class Field {
     }
 
     public func add(ballWithRadius radius: Float) {
-        let insetBounds = bounds.insetBy(dx: CGFloat(radius), dy: CGFloat(radius))
-
-        let x = Float(UInt32(insetBounds.minX) + arc4random_uniform(UInt32(insetBounds.width)))
-        let y = Float(UInt32(insetBounds.minY) + arc4random_uniform(UInt32(insetBounds.height)))
-        let position = Point(x: x, y: y)
+        let position = randomPoint(forBallWithRadius: radius)
 
         let dx = Float(5 - Int(arc4random_uniform(10)))
         let dy = Float(5 - Int(arc4random_uniform(10)))
@@ -114,6 +119,14 @@ public class Field {
         balls.removeAll(keepingCapacity: true)
     }
 
+    private func randomPoint(forBallWithRadius radius: Float) -> Point {
+        let insetBounds = bounds.insetBy(dx: CGFloat(radius), dy: CGFloat(radius))
+        let x = Float(UInt32(insetBounds.minX) + arc4random_uniform(UInt32(insetBounds.width)))
+        let y = Float(UInt32(insetBounds.minY) + arc4random_uniform(UInt32(insetBounds.height)))
+        let position = Point(x: x, y: y)
+        return position
+    }
+
     // MARK: - Metal Configuration
 
     private var device: MTLDevice?