metal_ball.swift

import PlaygroundSupport
import MetalKit

guard let device = MTLCreateSystemDefaultDevice() else {
    fatalError("GPU Is Not Supported")
}

let frame = CGRect(x: 0, y: 0, width: 600, height: 600)
let view = MTKView(frame: frame, device: device)

view.clearColor = MTLClearColor(red: 1, green: 1, blue: 0.8, alpha: 1)

// 1
let allocator = MTKMeshBufferAllocator(device: device)

// 2
let mdlMesh = MDLMesh(sphereWithExtent: [0.75, 0.75, 0.75], segments: [100,100], inwardNormals: false, geometryType: .triangles, allocator: allocator)

// 3
let mesh = try MTKMesh(mesh: mdlMesh, device: device)

guard let commandQueue = device.makeCommandQueue() else {
    fatalError("Could not create command queue.")
}

let shader = """
#include <metal_stdlib>
using namespace metal;

struct VertexIn {
    float4 position [[ attribute(0) ]];
};

vertex float4 vertex_main(const VertexIn vertex_in [[ stage_in ]]) {
    return vertex_in.position;
}

fragment float4 fragment_main() {
    return float4(.2, .2, .3, 1);
}
"""

let library = try device.makeLibrary(source: shader, options: nil)
let vertexFunction = library.makeFunction(name: "vertex_main")
let fragmentFunction = library.makeFunction(name: "fragment_main")

let pipelineDescriptor = MTLRenderPipelineDescriptor()
pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
pipelineDescriptor.vertexFunction = vertexFunction
pipelineDescriptor.fragmentFunction = fragmentFunction

pipelineDescriptor.vertexDescriptor = MTKMetalVertexDescriptorFromModelIO(mesh.vertexDescriptor)

let pipelineState = try device.makeRenderPipelineState(descriptor: pipelineDescriptor)

guard let commandBuffer = commandQueue.makeCommandBuffer(), let renderPassDescriptor = view.currentRenderPassDescriptor, let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) else {
    fatalError()
}

renderEncoder.setRenderPipelineState(pipelineState)
renderEncoder.setVertexBuffer(mesh.vertexBuffers[0].buffer, offset: 0, index: 0)

guard let subMesh = mesh.submeshes.first else {
    fatalError()
}

renderEncoder.drawIndexedPrimitives(type: .triangle, indexCount: subMesh.indexCount, indexType: subMesh.indexType, indexBuffer: subMesh.indexBuffer.buffer, indexBufferOffset: 0)

renderEncoder.endEncoding()

guard let drawable = view.currentDrawable else {
    fatalError()
}

commandBuffer.present(drawable)
commandBuffer.commit()

PlaygroundPage.current.liveView = view