First pass at a marching squares idea

MetaballsKit/MarchingSquares.swift

@@ -0,0 +1,64 @@
+//
+//  MarchingSquares.swift
+//  Metaballs
+//
+//  Created by Eryn Wells on 10/11/18.
+//  Copyright © 2018 Eryn Wells. All rights reserved.
+//
+
+import Foundation
+import Metal
+
+class MarchingSquares {
+    private var field: Field
+    private var sampleGridSize: Size
+
+    /// Samples of the field's current state.
+    private(set) var samples: MTLTexture?
+    /// Indexes of geometry to render.
+    private(set) var indexes: MTLTexture?
+
+    init(field: Field) {
+        self.field = field
+        sampleGridSize = Size(16)
+    }
+
+    func setupMetal(withDevice device: MTLDevice) {
+        let xSamples = Int(field.size.x / sampleGridSize.x)
+        let ySamples = Int(field.size.y / sampleGridSize.y)
+
+        let samplesDesc = MTLTextureDescriptor()
+        samplesDesc.textureType = .type2D
+        samplesDesc.width = xSamples
+        samplesDesc.height = ySamples
+        samplesDesc.pixelFormat = .depth32Float
+        samples = device.makeTexture(descriptor: samplesDesc)
+
+        let indexesDesc = MTLTextureDescriptor()
+        indexesDesc.textureType = .type2D
+        indexesDesc.width = xSamples - 1
+        indexesDesc.height = ySamples - 1
+        indexesDesc.pixelFormat = .a8Unorm
+        indexes = device.makeTexture(descriptor: indexesDesc)
+    }
+
+    func sampleField() {
+        guard let samples = samples else { return }
+
+        let xSamples = Int(field.size.x / sampleGridSize.x)
+        let ySamples = Int(field.size.y / sampleGridSize.y)
+        for xSample in 0..<xSamples {
+            let x = Float(xSample * Int(sampleGridSize.x))
+            for ySample in 0..<ySamples {
+                let y = Float(ySample * Int(sampleGridSize.y))
+                let sample = [field.sample(at: Float2(x: x, y: y))]
+
+                let origin = MTLOrigin(x: xSample, y: ySample, z: 0)
+                let size = MTLSize(width: 1, height: 1, depth: 1)
+                let region = MTLRegion(origin: origin, size: size)
+                let bytesPerRow = samples.width * MemoryLayout<Float>.stride
+                samples.replace(region: region, mipmapLevel: 0, withBytes: sample, bytesPerRow: bytesPerRow)
+            }
+        }
+    }
+}