Rendering Physically-Based ModelIO Materials

In this article, we’ll take a look at a portion of the ModelIO framework we haven’t used so far: materials. In previous articles, we’ve used ModelIO to do the heavy lifting of loading 3D geometry, but have loaded and applied textures manually. This ad hoc approach works when we only have a base color map, but quickly grows tedious as materials become more complicated. Here, we’ll take a deep dive into ModelIO materials and learn how to use them to perform basic physically-based rendering (PBR).

You can find the sample code for this article here.

This is not a tutorial on physically-based rendering. PBR has been a hot topic for the past several years, and other people have written excellent tutorials on the subject. Joey de Vries’ series is probably the most approachable. Also consider taking a look at the documentation for Google’s brand-new mobile-first rendering engine Filament. For more theoretical background, consult the following papers and resources:

The focus here is on how ModelIO represents materials, deemphasizing how a shader might render them. For this reason, the shaders for this article are a pared-down version of Apple’s LOD with Function Specialization sample, which is worth studying.

An example asset rendered by SceneKit, from the 2016 WWDC Session, Advances in SceneKit Rendering (

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Writing a Modern Metal App from Scratch: Part 2

In the previous article, we wrote enough Metal code to get the spinning silhouette of a teapot on the screen, but that still leaves a lot to be desired as far as a “modern” app is concerned. In this article, we’ll further flesh out the app and introduce lighting, materials, texturing, and managing multiple objects with scene graphs.

Remember that you can clone this Github repository to follow along with the sample code.

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Writing a Modern Metal App from Scratch: Part 1

Getting Started

This article is a quick introduction to how to use the Metal, MetalKit, and Model I/O frameworks in Swift. If you know your way around UIKit or Cocoa development, you should be able to follow along for the most part. Some things like shaders and matrices will be foreign to you, but you can learn them as you go about exploring Metal on your own. The purpose here is to give you a template to build on.

If you want to follow along without copy-pasting the code yourself, you can clone this GitHub repository and follow the instructions there.

First things first. Use Xcode to create a new project from the iOS Single View App template. Add import MetalKit at the top of the ViewController.swift file. We could use the Game template instead and have some of the boilerplate written for us, but writing it out long-hand will give us more of an appreciation for the moving parts. The Game template also includes a lot of moving parts that get in the way of understanding the basics.

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First Look at MetalKit

MetalKit is a forthcoming framework on iOS 9 and OS X El Capitan that greatly eases certain tasks such as presenting Metal content in a UIView or NSView, texture loading, and working with model data.

This post is an overview of the features offered by MetalKit. Many of our articles so far have focused on details that are not expressly related to Metal, but are instead required to give Metal something to draw on the screen: texture loading, 3D model loading, and setting up the interface between Metal and UIKit.

MetalKit seeks to make these tasks easier by providing classes that perform common operations. In this article, we’ll look briefly at these capabilities.

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