Codex: Pioneering iPad Note-Taking

The Vision

Create a digital notebook that matched the freedom of pen and paper while adding intelligent organization — all without requiring a stylus on the original iPad's screen.

iPad 1+

Original Hardware
Support

2013

Years before
Apple Pencil & PencilKit

$12.99

Premium Pricing Strategy

— for the time

Engineering Principles

Performance as a Feature

Responsiveness wasn't optional — it was the difference between users feeling like they were sketching or fighting the software.

Every optimization served the core experience.

Invisible Complexity

The most sophisticated systems (vector rendering, layer management, multi-dimensional filtering) were designed to be completely transparent to users.

Simple UI, complex engineering.

Hardware Realism

Supporting the original iPad meant facing hard constraints.

Solutions had to be elegant and efficient, not just functional.

Screenshots of the Codex app

Technical Architecture

Building a responsive, detailed drawing experience on 2013 iPad hardware required careful engineering across multiple domains:

Vector Ink Engine

Custom rendering system for smooth, pressure-free drawing

Real-time stroke capture and rendering
Vector-based storage for zoom without quality loss
Optimized rendering pipeline for iPad 1 hardware
Efficient memory management for complex drawings
Developed using Objective-C and manual memory management (pre-ARC).

Multi-Layer Architecture

Separate rendering layers for different content types

Independent image and ink layers
Non-destructive annotation system
Layer compositing for complex notes
Efficient layer visibility toggling
Image manipulation without affecting ink strokes
Powered by Core Animation and Core Graphics

Smart Organization System

Tag-based architecture with multi-dimensional filtering

Multi-tag support with AND/OR logic
Real-time search across titles and content
Position-based ordering with topic-aware persistence
Grid view system inspired by iWork apps
Visual relationship discovery through spatial arrangement
Data persistence and search using Core Data

Gesture & Input System

Native iPad interaction patterns

Pinch-to-zoom integration for detailed work
Seamless transition between navigation and drawing modes
Touch-optimized eraser and undo system
Fine precision finger-based drawing and hand writing
Clean, responsive UI that stayed out of the user's way

Data Management

Efficient storage and retrieval system

Vector data serialization
Image asset management
Fast note preview generation for grid view
Export pipeline to email, photo library, and printing
Template creation system

Performance Optimization

Critical for original iPad support

Efficient stroke simplification algorithms
View recycling for grid layout
Lazy loading of note content
Memory-conscious image handling
Smooth animations despite hardware constraints

Product Evolution & Impact

What Shipped

Full-featured note-taking app with vector drawing engine
Multi-topic tagging and filtering system
Position-based organization alongside time-based sorting
Multi-image insertion with resize, rotate, and annotation
Multiple paper styles, export options, and printing
Social sharing integration (Twitter, email, photo library)

Engineering Retrospective

What I'd approach differently today:

Cloud sync: In 2013, iCloud was nascent. Today, multi-device sync would be table stakes
Handwriting recognition: Modern ML would enable OCR search within handwritten notes
Apple Pencil optimization: Pressure sensitivity and tilt would add another dimension
Collaborative features: Real-time collaboration wasn't feasible then but would be essential now
Accessibility: VoiceOver support and other a11y features would be prioritized from day one
Go-to-Market Strategy: Lesson learnt: launch early (MVP), iterate often, and let real use guide refinement.

What still holds up: The core architecture: vector-based drawing, layer separation, and tag-based organization - remains sound. The focus on performance and unobtrusive UI are timeless principles.