added particles

README.md

@@ -29,3 +29,4 @@ Repository to accompany the following blog posts:
 - [Introducing Metal 2](http://metalkit.org/2017/06/30/introducing-metal-2.html)
 - [Using ARKit with Metal](http://metalkit.org/2017/07/29/using-arkit-with-metal.html)
 - [Using ARKit with Metal part 2](http://metalkit.org/2017/08/31/using-arkit-with-metal-part-2.html)
+- [Working with Particles in Metal](http://metalkit.org/2017/09/30/working-with-particles-in-metal.html)

particles/particle.playground/Contents.swift

@@ -0,0 +1,9 @@
+
+import MetalKit
+import PlaygroundSupport
+
+let frame = NSRect(x: 0, y: 0, width: 400, height: 400)
+let delegate = MetalView()
+let view = MTKView(frame: frame, device: delegate.device)
+view.delegate = delegate
+PlaygroundPage.current.liveView = view

particles/particle.playground/Resources/Shaders.metal

@@ -0,0 +1,30 @@
+
+#include <metal_stdlib>
+using namespace metal;
+
+struct Particle {
+    float2 center;
+    float radius;
+};
+
+float distanceToParticle(float2 point, Particle p) {
+    return length(point - p.center) - p.radius;
+}
+
+kernel void compute(texture2d<float, access::write> output [[texture(0)]],
+                    constant float &time [[buffer(0)]],
+                    uint2 gid [[thread_position_in_grid]]) {
+    int width = output.get_width();
+    int height = output.get_height();
+    float2 uv = float2(gid) / float2(width, height);
+    float2 center = float2(0.5, time);
+    float radius = 0.05;
+    float stop = 1 - radius;
+    if (time >= stop) { center.y = stop; }
+    else center.y = time;
+    Particle p = Particle{center, radius};
+    float distance = distanceToParticle(uv, p);
+    float4 color = float4(1, 0.7, 0, 1);
+    if (distance > 0) { color = float4(0.2, 0.5, 0.7, 1); }
+    output.write(float4(color), gid);
+}

particles/particle.playground/Sources/MetalView.swift

@@ -0,0 +1,57 @@
+
+import MetalKit
+
+public class MetalView: NSObject, MTKViewDelegate {
+
+    public var device: MTLDevice! = nil
+    var queue: MTLCommandQueue! = nil
+    var cps: MTLComputePipelineState! = nil
+    var timerBuffer: MTLBuffer! = nil
+    var timer: Float = 0
+
+    override public init() {
+        super.init()
+        device = MTLCreateSystemDefaultDevice()
+        queue = device.makeCommandQueue()
+        registerShaders()
+    }
+
+    func registerShaders() {
+        guard let path = Bundle.main.path(forResource: "Shaders", ofType: "metal") else { return }
+        do {
+            let input = try String(contentsOfFile: path, encoding: String.Encoding.utf8)
+            let library = try device.makeLibrary(source: input, options: nil)
+            guard let kernel = library.makeFunction(name: "compute") else { return }
+            cps = try device.makeComputePipelineState(function: kernel)
+        } catch let e {
+            Swift.print("\(e)")
+        }
+        timerBuffer = device.makeBuffer(length: MemoryLayout<Float>.size, options: [])
+    }
+
+    func update() {
+        timer += 0.01
+        let bufferPointer = timerBuffer.contents()
+        memcpy(bufferPointer, &timer, MemoryLayout<Float>.size)
+    }
+
+    public func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}
+
+    public func draw(in view: MTKView) {
+        if let drawable = view.currentDrawable,
+           let commandBuffer = queue.makeCommandBuffer(),
+           let commandEncoder = commandBuffer.makeComputeCommandEncoder()
+        {
+            commandEncoder.setComputePipelineState(cps)
+            commandEncoder.setTexture(drawable.texture, index: 0)
+            commandEncoder.setBuffer(timerBuffer, offset: 0, index: 0)
+            update()
+            let threadGroupCount = MTLSizeMake(8, 8, 1)
+            let threadGroups = MTLSizeMake(drawable.texture.width / threadGroupCount.width, drawable.texture.height / threadGroupCount.height, 1)
+            commandEncoder.dispatchThreadgroups(threadGroups, threadsPerThreadgroup: threadGroupCount)
+            commandEncoder.endEncoding()
+            commandBuffer.present(drawable)
+            commandBuffer.commit()
+        }
+    }
+}

particles/particle.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

particles/particle.playground/timeline.xctimeline

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Timeline
+   version = "3.0">
+   <TimelineItems>
+   </TimelineItems>
+</Timeline>