CLAUDE.md: guide for AI coding agents

This file is read by Claude Code (and mirrored in AGENTS.md for Codex and other agents). It explains how this repo is organised and how to extend it. Follow CONTRIBUTING.md for every new effect.

What this project is

A SwiftUI counterpart to web "motion library" galleries: a collection of reusable motion effects, organised on two axes:

• Component (MotionComponent): text, button, card, shape, background, number, particle (Particle & 3D), transition
• Trigger (MotionTrigger): appear, tap, press, drag, hover, scroll, change, loop

Each effect has: a public API in MotionLibrary, a demo view, and a catalog entry with usage code + an AI prompt shown in the MotionGallery browser UI. The catalog is the source of truth for everything AI-facing (llms.txt, the Agent Skill, the Cursor rule, the MCP server's JSON), which Scripts/generate-docs.sh regenerates.

Architecture

Package.swift                         # tools 5.9, iOS 17 / macOS 14 / visionOS 1
Sources/MotionLibrary/<Component>/    # effects, public API, zero dependencies
Sources/MotionShaders/                # optional Metal shader effects; Shaders/<Name>.metal per effect
Sources/MotionGallery/
  Model/MotionEffect.swift            # MotionComponent, MotionTrigger, MotionEffect
  Catalog/MotionCatalog.swift         # static list of every effect (display order)
  Catalog/Demos.swift                 # demo views used by the catalog
  Views/                              # gallery grid, detail view, shared components
Docs/gifs/, Docs/motion-catalog.json  # README previews + generated catalog JSON
llms.txt, llms-full.txt               # generated
skills/swiftui-motion/                # generated Agent Skill
.cursor/rules/swiftui-motion.mdc      # generated Cursor rule
mcp/server.mjs                        # zero-dependency MCP server (reads the JSON)
Examples/MotionLibraryDemo/           # iOS demo app (XcodeGen project.yml + committed .xcodeproj) + scroll UI tests
Scripts/                              # check-build, check-standalone, generate-docs, record-readme-gifs, record-simulator-gifs, make-social-preview

• MotionLibrary must never import MotionGallery.
• Every effect must stay copyable on its own: helpers shared by several effects live in Sources/MotionLibrary/Support/, never inside another effect's file. Scripts/generate-docs.sh detects each effect's extra files (files in the catalog JSON, the note in each README cell) and Scripts/check-standalone.sh type-checks every effect from just those files.
• MotionEffect.demo is @MainActor. Call it only from view bodies or @MainActor helpers.
• Catalog usage and prompt strings use raw multi-line strings #""" … """# so key paths like \.self don't break.
• Never hand-edit generated files (README grids between the effects markers in README.md and README.zh-TW.md, llms*.txt, Docs/motion-catalog.json, skills/, .cursor/rules/). Change the catalog and run Scripts/generate-docs.sh.
• The README is bilingual: README.md (English) and README.zh-TW.md (Traditional Chinese), each with a language switcher at the top. When you change the prose outside the effects markers in one, make the same change in the other. Chinese category and trigger names for the grid live in ReadmeLanguage in Scripts/DocsGenerator/main.swift.

Rules

• Pure SwiftUI. No third-party dependencies in either target.
• Don't raise the deployment targets without asking the maintainer.
• The demo app's .xcodeproj is generated from Examples/MotionLibraryDemo/project.yml: edit the YAML and run xcodegen generate in that folder, never the project file. New source files in its folders need a regenerate too.
• Keep public API names short and SwiftUI-like (.shimmer(), not .applyShimmerEffect()).
• Every effect file ends with a #Preview.
• Don't rename existing catalog ids or public API (it's a library; breaking changes need a major version).
• Shader effects go in Sources/MotionShaders/<Name>.swift + Shaders/<Name>.metal, with sourceFile: "MotionShaders/<Name>.swift" in the catalog (paths starting with MotionShaders/ are resolved from Sources/). The scripts use Xcode's toolchain when Xcode is installed (it can compile Metal); with only the Command Line Tools the shaders are swapped for a placeholder so the Swift still compiles.
• Mark every path(in:) and animatableData nonisolated. Apps in the Swift 6 language mode (and with MainActor default isolation) infer view types as MainActor, and a copied effect then fails with "conformance … crosses into main actor-isolated code". SWIFT_FLAGS="-swift-version 6 -default-isolation MainActor" Scripts/check-standalone.sh checks it.
• Keyframes must have a positive duration (a 0 s keyframe crashes), and never feed a raw clock value into dashPhase (Core Graphics walks the dash pattern up to it and hangs): wrap it to one dash period.
• Scroll-driven effects: test them with real scrolling on iOS. Add a full-screen example and a UI test to Examples/MotionLibraryDemo (its tests drag with a finger and assert on accessibility frames, which follow visualEffect transforms), and run them with xcodebuild test -project Examples/MotionLibraryDemo/MotionLibraryDemo.xcodeproj -scheme MotionLibraryDemo -destination 'platform=iOS Simulator,name=iPhone 17 Pro' CODE_SIGNING_ALLOWED=NO. In visualEffect, apply scaleEffect before the pinning offset, or the scale shrinks the offset and the view drifts away. Don't rely on a PreferenceKey getting out of an iOS ScrollView: drive the effect from visualEffect geometry instead. The macOS GIF recorder can't animate scrolling, so record these GIFs with Scripts/record-simulator-gifs.sh <id> (and add the id to simulatorRecorded in Scripts/ReadmeGIFs/main.swift).
• Releases: bump packageVersion in Scripts/DocsGenerator/main.swift and the from: install line in both READMEs, run Scripts/generate-docs.sh, then tag the commit with the bare version (0.4.0, no v). SwiftPM resolves from: against these tags.
• After adding or changing an effect, run Scripts/generate-docs.sh (README grid, llms.txt, Skill, Cursor rule, catalog JSON) and record its GIF.

Verifying changes

Full Xcode isn't required. The #Preview macro needs Xcode's plugin, so the scripts build a preview-stripped copy of the package (Scripts/stage-package.sh):

Scripts/check-build.sh            # compile MotionLibrary + MotionGallery for macOS
Scripts/check-standalone.sh       # each effect compiles from just its listed files (after generate-docs)
SWIFT_FLAGS="-swift-version 6 -default-isolation MainActor" Scripts/check-standalone.sh  # same, as a Swift 6 app
Scripts/generate-docs.sh          # regenerate catalog-derived files (--check to verify)
Scripts/record-readme-gifs.sh id  # record Docs/gifs/<id>.gif off-screen, then look at the frames
Scripts/record-simulator-gifs.sh  # GIFs that need real scrolling, recorded in the iOS Simulator
Scripts/round-gif-corners.py      # transparent rounded corners (both recorders run it; needs Pillow and NumPy)
Scripts/record-readme-gifs.sh hero  # Docs/hero.gif, the README's top mosaic (Scripts/ReadmeGIFs/Hero.swift)
swift Scripts/make-social-preview.swift  # Docs/social-preview.png, upload in Settings → Social preview

With Xcode, also build for iOS and visionOS (DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer xcodebuild -scheme MotionLibrary-Package -destination 'generic/platform=iOS Simulator' -derivedDataPath .build/xcode build, same with visionOS Simulator) and check effects in the canvas. sensoryFeedback needs visionOS 26, so use the internal .haptic(…) helpers instead.

Roadmap (suggested next tasks)

1. Make v0.1 compile (done for macOS; still check iOS in Xcode and tune demo sizes in the grid).
2. Demo app (done: Examples/MotionLibraryDemo, the gallery plus full-screen scroll examples and their UI tests).
3. Reduce Motion (done: every looping or large-movement effect falls back to a fade or a static state).
4. More effects. v0.2 added gradient sweep, blur-in, marquee, wave text, magnetic, hold-to-confirm, status button, glow border, flip, swipe stack, parallax carousel, expandable card, checkmark, confetti, loaders, morphing blob, particle field, starfield, cover flow and float 3D. v0.3 added 40 more (count-up, split text, rotating text, glitch, circular text, focus text, highlighter, shine, jelly, click spark, like button, animated symbol, liquid toggle, hero expand, spotlight card, magnifying dock, jiggle, fan stack, draw-on, progress ring, skeleton, sliding tabs, mesh gradient, retro grid, border beam, waves, film grain, flashlight, fireworks, snowfall, floating reactions, warp tunnel, holographic card) and the Transition component (iris, blinds, clock wipe, pixel dissolve, poof, swoosh, film exposure). v0.4 added 45 more (morphing text, neon, karaoke, weight wave, exploding text, gooey menu, slide to confirm, download button, star rating, bouncy tab bar, scratch card, stacking cards, deck shuffle, looping carousel, drag to dismiss, shrinking/stretchy headers, reading progress, lava lamp, matrix rain, dot grid, meteors, flow field, split-flap, slot machine, price ticker, animated chart, needle gauge, physics emoji, shatter, cube, dot globe, bubbles, fireflies, circular reveal, liquid swipe, page turn, glitch transition, origami) and the Shader component in the separate MotionShaders product (water ripple, pixellate, chromatic aberration, CRT, heat haze, noise dissolve). v0.5 added 27 more (liquid fill text, pull cord, island pill, hover lift, marquee wall, photo develop, network, topographic lines, day & night sky, contribution grid, analog clock, flock, ink trail, rain on glass, orbits, ink bleed, zoom blur) and 10 shaders (disintegrate, genie, glass lens, swirl, kaleidoscope, halftone, dither, thermal, flag wave, Voronoi cells). New catalog entries go in MotionCatalog+v05.swift / MotionCatalog+ShadersV05.swift and demos in Demos+v05.swift. Before adding one, check it doesn't duplicate an existing effect (for example a burning-paper transition is noise-dissolve, equaliser bars are MotionLoader(.bars)).
5. "Copy as AI prompt" for the whole filtered list, and a "View source" link to GitHub from the detail view.
6. Docs site: DocC catalog (README GIFs and AI-facing docs are done).
7. Tests: Scripts/generate-docs.sh already fails on duplicate ids, a missing api or a missing source file. Snapshot tests are optional.

Commit style

Conventional commits, e.g. feat(text): add gradient sweep, fix(gallery): grid cell clipping.