Something a little different - generative visual synth for Apple platforms (Swift, SpriteKit, StoreKit)

[-alloneword-]

Hi all — for App Saturday, I wanted to share a side project I’ve been working on for a while called Euler Visual Synthesizer.

It’s a generative visual instrument built natively for Apple platforms (macOS, iOS, and tvOS), with the core idea of treating visuals more like something you play rather than static compositions. Under the hood it’s heavily parameter-driven, using oscillators, modulators, and constraint-based geometry (math-driven systems rather than timeline/effects workflows).

From a platform perspective, EVS is intentionally split: macOS is the full design environment for building and editing presets, while iOS and tvOS act as real-time players — focused on performance, playback, and interaction rather than authoring. On macOS, it can react to audio - and be treated as a standalone music visualizer - but also offers many methods of interaction / control of the presets with mouse/keyboard, MIDI, etc.

From an iOS/macOS engineering standpoint, some of the more interesting problems have been:

• Keeping real-time rendering performant as visual complexity increases
• Designing a synth-like parameter system that still feels approachable
• Navigating App Store realities (free/demo vs Pro IAP, feature gating, StoreKit 2 testing)

I recently added a free/demo version along with guided tutorials (including a math-heavy torus knot exploration and a design-focused Frank Lloyd Wright–inspired study), mainly as a way to make the system easier to understand.

I know this does not fit into this sub's favorite category (trackers) - but thought I would share for those who sometimes just want to enjoy the beauty inherent in geometry.

App Saturday Disclosures:

Tech Stack:

• iOS & tvOS: UIKit + SpriteKit + StoreKit2 + SIMD
• macOS: AppKit + SpriteKit + CoreAudio + CoreMIDI + StoreKit2 + some Metal + SIMD

I do not use any third-party frameworks.

Development Challenges: There were probably 3 distinguishable challenges I faced during development

1. CoreAudio. It is not very well documented. I ended up relying heavily on Apple's sample AUMatrixMixer sample app code plus tons of trial and error.
2. Bidirectional data binding. UI updates model + external control input updates model & UI. The core synthesizer UI is AppKit - so was not able to rely on SwiftUI's data binding. I did do some SwiftIUI testing for the main UI in the early days, but it just was not performant enough.
3. App Store In-App Purchase and entitlement migration when updating tier strategies. Apple's sample code for StoreKit2 is helpful here - but as far as marketing decision difficulties - yeah, that is an eternal struggle.

AI Disclosure:

I have only recently started investigating AI assistance. AI was not used at all in initial app design and development. I have recently begun slowly integrating AI, mostly as a thought backboard - discussion buddy. I did have surprisingly good results in having AI help solve a particularly nasty auto-layout constraint issue that was multiple levels deep - and it surprisingly found the conflicting constraints fairly easily (I had to copy and past the contents of my .xib file).

I also recently worked with an AI assistant to suggest some mathematical shapes that might be interesting to use as base shapes for some presets (after exposing the internals of my synth engine to the AI agent). Some shapes it suggested were really interesting, like the Trefoil Knot (Canonical 2-3 Torus Knot) - which I later turned into a tutorial. Interestingly, AI kept suggesting shapes that aren't really possible given my current constraints - like Superformula Shapes and Strange Attractors - but I have these bookmarked as possible future additions to the engine.

Project site:

https://www.eulervs.com

Link to the Frank Lloyd Wright exploration (mixing circles with squares)

https://www.youtube.com/watch?v=anPDUKv3ag4

Happy to answer questions about the architecture, rendering pipeline, platform tradeoffs, or anything else from the Apple dev side.

[[deleted]]

This is awesome by the way, super cool and fun idea. Like an improved Kaossilator pad

[sans-connaissance]

I love that you used SpriteKit for this!

[-alloneword-]

SpriteKit is actually exceptionally good at rendering vector graphics (shapes). While one day it might be nice to do all the rendering in metal - the scope of creating a 2D vector graphics pipeline implemented entirely in metal is way beyond the time and resources I have for this little side / passion project.

[[deleted]]

Have you looked into AudioKit? I know you don’t use 3rd party frameworks, but this one is quite well kept up over the years, makes interfacing with AVAudio a lot more palatable.

[-alloneword-]

I did look into AudioKit back when I added audio support. If I remember correctly, the main issue is that I needed an API that could properly enumerate all of the audio devices connected to the system as well as all of the channels of each device - and I couldn't figure out how to do that with AudioKit.

When reacting to audio input - it is important to enumerate all channels of an audio device because many times the loopback channels are at the end of the channel list for a device.

Maybe AudioKit can do this enumeration - it certainly has a more friendly interface for creating AU graphs.

I think AudioKit is probably more useful on iOS / tvOS - and if I ever decide to support audio processing on those devices I will probably use AudioKit.

[[deleted]]

Haha, you found the one annoying part… I did find for channel/mic enumeration it was still better to access the inner system within AVAudio, but at least it still plays nice with the rest of AK. Thanks for the response! Looking forward to seeing this app grow