Underdraw

Underdraw helps you draw by tracing. Pick an image and it appears semi-transparent over the live rear-camera feed, so you can trace it onto the paper below your phone. There is also a no-camera sketch mode, which shows the image full-screen at max brightness so you can trace with paper on top of the screen.

It's built with Expo (SDK 57) and React Native, and is fully offline: no accounts and no analytics.

Features

• Trace mode – overlay an image on the camera, then move, scale and rotate it with two fingers. You can also adjust opacity, lock, flip, reset and use the torch.
• Sketch mode – the image on a bright white screen.
• Editor – original, grayscale and outline line-art filters, plus crop.
• Home – 108 starter templates in 9 categories, recents, and resume where you left off.
• Light and dark theme, onboarding, and a camera and photo permission flow.

🛠️ Tech Stack

• Expo + expo-router – dev builds and tag-driven EAS releases for iOS and Android
• react-native-vision-camera v5 – live camera feed and torch
• Reanimated + Gesture Handler – overlay transforms on the UI thread for 60fps
• React Native Skia – image filters, run once on the overlay rather than per camera frame
• Uniwind (Tailwind v4) – styling with a custom design system, Gluten and Hanken Grotesk fonts
• Zustand + MMKV – persisted settings and recents
• Next.js – marketing site with privacy policy and support pages