Swift on August Feng

AWS Swift SDK and email addresses as SSO session names

Fri, 12 Jun 2026 00:00:00 +0000

About

I'm a big fan of how AWS's SDK authentication mechanism is standardized across languages and also portable across environments.

Hint: The credential provider chain allows a program to authenticate when running locally and fall back to the IAM infrastructure when it's running in an AWS environment.

All good until Swift

When developing locally, I like to use the IAM Identity Center credential provider and avoid configuring access keys.

Shorthand Dot Syntax In Swift

Sun, 26 Oct 2025 00:00:00 +0000

About

Just dumping some code from a short study done on shorthand dot syntax in Swift. I tried three different ways:

Stored type properties on the method parameter type (struct)
Stored type properties on the extension of the method parameter type (struct)
Stored type properties and cases on the method parameter type (enum)

Code

import SwiftUI

// example 1

extension String {
    static let helloworld: String = "helloworld"
}

struct Foobar {
    func run(helloworld: String) {
        print(helloworld)
    }
}

// example 2

struct Helloworld {
    let text: String

    static let french: Helloworld = Helloworld(text: "bonjour!")
    static let english: Helloworld = Helloworld(text: "Hello, World!")
}

struct Foobaz {
    func run(helloworld: Helloworld) {
        print(helloworld.text)
    }
}

// example 3

enum Bye {
    case french(String)
    case english(String)
    case other(String)
    static let mandarin: Bye = Bye.other("再见")
    static let spanish: String = "adios!"
}

struct Qux {
    func run(bye: Bye) {

    }
}

struct ContentView: View {
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundStyle(.tint)
            Text("Hello, world!")
        }
        .padding()
        .onAppear {
            // XXX: You can choose stored type properties on an extension.
            let foobar = Foobar()
            foobar.run(helloworld: .helloworld)

            // XXX: You can choose stored type properties.
            let foobaz = Foobaz()
            foobaz.run(helloworld: .english)

            // XXX: You can choose both case and stored type properties.
            let qux = Qux()
            qux.run(bye: .french("adieu."))
            qux.run(bye: .mandarin)
            // qux.run(bye: .spanish) // XXX: won't compile because it resolves to a string, but auto-completion offers it.
        }
    }
}

Drawing text with Core Graphics

Fri, 24 Oct 2025 00:00:00 +0000

About

I've learned to draw text with SwiftUI's Text view.

I've learned to draw text using AppKit and TextKit.

I've also learned to draw text using CoreText.

Is it time to learn to draw text using Core Graphics? Yes.

Code

I'll just dump the code here for posterity and go walk the dog now.

import CoreText
import SwiftUI

class FoobarView: NSView {
    override func draw(_ dirtyRect: NSRect) {
        let font = CTFont(.system, size: 12, language: nil)
        let helloworld = Array("foo".utf16)
        var glyphs = [CGGlyph](repeating: 0, count: helloworld.count)
        let success = CTFontGetGlyphsForCharacters(
            font,
            helloworld,
            &glyphs,
            helloworld.count
        )

        if let context = NSGraphicsContext.current?.cgContext, success {
            // XXX: On the CGFont, it says that the context won't draw unless this is called.
            // XXX: https://developer.apple.com/documentation/coregraphics/cgfont/init(_:)-1p4b#Discussion
            // XXX: It doesn't mention that setFontSize also needs to be called though.
            let font = CTFontCopyGraphicsFont(font, nil)
            context.setFont(font)
            context.setFontSize(12)
            context.showGlyphs(
                glyphs,
                at: [
                    CGPoint(x: 0, y: 0),
                    CGPoint(x: 8, y: 0),
                    CGPoint(x: 16, y: 0),
                ]
            )
        }
    }
}

struct FoobarRepresentableView: NSViewRepresentable {
    func makeNSView(context: Context) -> some NSView {
        FoobarView()
    }

    func updateNSView(_ nsView: NSViewType, context: Context) {}
}
struct ContentView: View {
    var body: some View {
        FoobarRepresentableView()
            .padding()
    }
}

#Preview {
    ContentView()
}

Coordinate System on MacOS

Sat, 18 Oct 2025 00:00:00 +0000

About

This is just a random expression of my learning about the coordinate system in MacOS.

Graphics Context

The rendering engine (Quartz 2D) for Mac uses a typical Cartesian coordinate system, which means the origin (0,0) is at the bottom left corner and the axis grow respectively to the left and up.

SwiftUI's coordinate system

In SwiftUI, you'll most often see a modified coordinate system where the origin is at the top left and the axis grow to the left and down.

Part 5: The IOKit API

Mon, 14 Jul 2025 00:00:00 +0000

About

We're at the last part of the series! This part will explore the IO framework.

Learnings

Enumerating all HID devices

This program will enumerate all HID devices:

  import Foundation
  import IOKit
  import IOKit.hid

  func run(and cb: IOHIDDeviceCallback) {
      let manager = IOHIDManagerCreate(
        kCFAllocatorDefault,
        0x0  // https://developer.apple.com/documentation/iokit/1645245-anonymous/kiohidmanageroptionnone
      )

      let matching: [CFString: NSNumber] = [:]

      // Match everything for now
      IOHIDManagerSetDeviceMatching(manager, matching as NSDictionary)

      // Schedule the manager
      IOHIDManagerScheduleWithRunLoop(
        manager,
        CFRunLoopGetMain(),
        CFRunLoopMode.defaultMode!.rawValue
      )

      // print reference when a matching device is detected
      IOHIDManagerRegisterDeviceMatchingCallback(
        manager,
        { (_,_,_, device) in
            print(device)
        },
        nil)

      // Start the manager
      let _ = IOHIDManagerOpen(
        manager,
        IOOptionBits(kIOHIDOptionsTypeNone) // XXX: use `kIOHIDOptionsTypeSeizeDevice~ to perform an exclusive link when matching
      )
      CFRunLoopRun()
  }

  run()

I'm interested in using my ZSA Moonlander as input device, so I identified its Vendor ID and Product ID.

Part 2: The HotKeys API

Sun, 13 Jul 2025 00:00:00 +0000

About

In a previous article, I wrote about how I'd like to learn about all the APIs that I use to implement shortcuts in MacOS.

The last article detailed the CGEvent API. In this article, we'll be tackling an old deprecated Carbon API.

Learnings

NSApplicationDelegate

Unlike the previous API, this API requires a fully fledged GUI.

I didn't really want to try integrating this deprecated API with SwiftUI, so I build the GUI with NSApplicationDelegate instead.

Part 3: The NSEvent API

Sun, 13 Jul 2025 00:00:00 +0000

About

In part 2, I used the deprecated Carbon API to listen for shortcuts. In this part, I'll be using what I think is its successor: the NSEvent API.

Learnings

NSApplicationDelegate

Like in part 2, this implementation requires an application lifecycle. The NSApplicationDelegate is able to provide one.

A global monitoir and a local monitor

When the program is not focused, events are sent to the global monitor. And when the program is focused, events are sent to the local monitor.

Part 4: The CGS API

Sun, 13 Jul 2025 00:00:00 +0000

About

This is an interesting one! The CGS API is not public one so I'm getting no help from the IDE.

Learnings

@_silgen_name

The @_silgen_name attribute used to called @asmname, and Russ Bishop likens it to DllImport or extern.

I have experience with the later too so I understand we're going to ask the compiler to find the implementation in elsewhere.

I was lucky and found an open source project that did the work of the function signatures so that I don't need to (learn and) reverse the library myself.

Part 1: The CGEvent API

Fri, 11 Jul 2025 00:00:00 +0000

About

I'd like to implement an application that can be opened in a similar manner that Ctrl-Space opens Spotlight.

I asked ChatGPT to enumerate a few open source projects that deploys these feature so I can study how their implementations.

As I read the codebases, I understood that there are many ways to approach this implementation.

I was fortunate that the alt-tab-macos is open source and documents a list of APIs that seem to be able to implement the mechanism. The list includes the following APIs:

An app that snaps

Thu, 10 Jul 2025 00:00:00 +0000

About

My productivity at a computer is highly dependent on having shortcuts to snap windows.

The MacOS did not come have native snapping capabilities until recently. And still, it's not all apps that have them enabled.

I've been studying MacOS development for the last month, and thought it was finally time that I challenged myself to implementing an actual tool without following instructions.

Adventure

I was very fortunate that the Rectangle project is open. I easily able to find the line of code that performed the snapping action.

The default tilesize on macos

Wed, 09 Jul 2025 00:00:00 +0000

About

I really like to maintain defaults on a system, including preferences. This means I like to keep my MacOS's dock tile size to the default size.

I used to grep my shell history for this command defaults delete com.apple.dock "tilesize" && killall Dock and re-run it every time the dock got resized.

I thought it'd be fun to try to use Swift do to this instead.

Calculating the existing dock height

The approach suggested by ChatGPT is to use the NSScreen API.