First pass at a marching squares idea

Metaballs.xcodeproj/project.pbxproj

@@ -46,6 +46,8 @@
 		C0FF7CBC216B002E0081B781 /* PreferencesViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = C091616F1F3F5AE6009C4263 /* PreferencesViewController.swift */; };
 		C0FF7CBF216B00570081B781 /* MetalKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = C0FF7CBD216B00570081B781 /* MetalKit.framework */; };
 		C0FF7CC0216B00570081B781 /* Metal.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = C0FF7CBE216B00570081B781 /* Metal.framework */; };
+		C0FF7CC2217020820081B781 /* MarchingSquares.swift in Sources */ = {isa = PBXBuildFile; fileRef = C0FF7CC1217020820081B781 /* MarchingSquares.swift */; };
+		C0FF7CC3217020820081B781 /* MarchingSquares.swift in Sources */ = {isa = PBXBuildFile; fileRef = C0FF7CC1217020820081B781 /* MarchingSquares.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -105,6 +107,7 @@
 		C0FF7CB1216AFD890081B781 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		C0FF7CBD216B00570081B781 /* MetalKit.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = MetalKit.framework; path = Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS12.0.sdk/System/Library/Frameworks/MetalKit.framework; sourceTree = DEVELOPER_DIR; };
 		C0FF7CBE216B00570081B781 /* Metal.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = Metal.framework; path = Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS12.0.sdk/System/Library/Frameworks/Metal.framework; sourceTree = DEVELOPER_DIR; };
+		C0FF7CC1217020820081B781 /* MarchingSquares.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MarchingSquares.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -203,6 +206,7 @@
 			isa = PBXGroup;
 			children = (
 				C0BBE3A31F2E81C700E68524 /* Metaballs.swift */,
+				C0FF7CC1217020820081B781 /* MarchingSquares.swift */,
 				C0CE7BFF1F362C3F001516B6 /* Geometry.swift */,
 				C0DF1D781F3789DC0038B0A0 /* Memory.swift */,
 				C0FF7C9C216A6DE00081B781 /* Math.swift */,
@@ -433,6 +437,7 @@
 				C0FF7C992168062C0081B781 /* Shaders.metal in Sources */,
 				C0FF7C9A2168062C0081B781 /* Preferences.swift in Sources */,
 				C0FF7C9E216A6DE00081B781 /* Math.swift in Sources */,
+				C0FF7CC3217020820081B781 /* MarchingSquares.swift in Sources */,
 				C0FF7C972168062C0081B781 /* Memory.swift in Sources */,
 				C0FF7C9B2168062C0081B781 /* PreferencesViewController.swift in Sources */,
 				C0B906E91F455D1A00B5F89B /* MetaballsSaverView.swift in Sources */,
@@ -456,6 +461,7 @@
 				C0FF7C932168062B0081B781 /* Preferences.swift in Sources */,
 				C0BBE36B1F2E816500E68524 /* AppDelegate.swift in Sources */,
 				C0FF7C9D216A6DE00081B781 /* Math.swift in Sources */,
+				C0FF7CC2217020820081B781 /* MarchingSquares.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

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)
+            }
+        }
+    }
+}