Real 3D → Three.js via the adapter
This is the one pin to state every time. For anything with genuine depth, lighting, or a camera — a rotating product, a scene you move through, surfaces that catch light — ask for Three.js explicitly:Build the scene in Three.js via the adapter: a product model on a turntable, one key light and a soft fill, slow rotation.
- ❌
isometric cards floating in CSS 3D with perspective - ✅
build the isometric scene in Three.js via the adapter, with real depth and lighting
perspective transforms skew flat planes — they read flat the moment lighting or parallax matters, because there is no light source and no camera, only projected rectangles. Three.js is a first-party seek-safe runtime (hf-seek events plus window.__hfThreeTime), so a real 3D scene renders frame-accurately like everything else. This is a validated default, not a preference — treat “real 3D” as “Three.js” unless you specifically want a flat, stylized fake-3D look.
Camera moves are part of the same rule. A “drone orbit”, dolly, or push-in only exists where there’s an actual camera:
A seek-driven Three.js drone orbit — the camera sweeps a continuous arc; impossible with CSS transforms.
- ❌
a drone-orbit camera move around the logo(with no runtime named — CSS has no camera to orbit) - ✅
orbit the camera around the logo — Three.js via the adapter
Existing animation files → Lottie
If you already have a designed animation — an After Effects export, a.json or .lottie file, an icon animation from a designer — don’t ask the agent to redraw it. Point at the file and ask for Lottie:
Play this Lottie file (assets/loader.lottie) centered, then fade to the title.
The Lottie adapter seeks the existing animation frame-by-frame, so the designer’s work renders exactly as authored. Asking the agent to recreate it in GSAP throws away the source and lands somewhere approximate.
Simple UI and text motion → the default
Fades, slides, staggers, counters, kinetic type, hover-style reveals — the everyday motion — is what GSAP does natively, and it’s already the default. You don’t name a runtime here; you describe the motion (see Premium motion):The headline slides up per word, staggered 0.1s apart, easing out as it lands.CSS keyframes and the Web Animations API are also supported adapters, worth naming only when you’re bringing existing CSS
@keyframes or WAAPI code you want kept as-is. For a fresh ask, let the default handle it.
Scene-to-scene → shader transitions
Motion within a scene is one thing; the handoff between scenes is another. For a designed transition — a wipe, a glitch, a liquid dissolve — ask for a shader transition at that specific moment:Hard-cut between the first three scenes; use a shader transition (glitch) into the final logo scene.Name the moments — shader transitions are for the two or three beats that deserve them, not every cut. See Transitions for the vocabulary.
Determinism surfaces in the prompt
Every runtime renders under the same determinism contract: the frame clock ist = frame / fps, and there is no wall clock, no live network at render time, and no unseeded randomness. Two asks bump into this, so phrase them accordingly:
-
❌
fetch the current BTC price and count up to it— a render-time fetch isn’t allowed; the render must be reproducible -
✅
count up to $67,400(a fixed value baked in), orread the target from a variable I pass at render time -
❌
scatter 200 particles randomly— unseeded randomness renders differently each frame and breaks reproducibility -
✅
scatter 200 particles from a seeded random layout— say seeded and the positions are stable across frames and re-renders
Related
Frame adapters (concept)
The seek-by-frame contract and the full list of supported runtimes.
Deterministic rendering
Why no live data and no unseeded randomness — the reproducibility guarantee.
Premium motion
Describing everyday GSAP motion so it doesn’t read as cheap.
Transitions
Naming the scene-to-scene handoffs worth a shader transition.