---
title: Runtimes and 3D
description: "GSAP is the default and you rarely name it. Real 3D, existing animation files, and scene transitions each have a runtime worth pinning in the prompt."
---

import { DocsVideo } from "/snippets/docs-video.jsx";

Level 2's copy-paste examples include an isometric-cards prompt that asks to
"Build the scene in Three.js via the adapter." This chapter is why that line is
there. It's also the rest of the runtime map, for the cases where GSAP isn't the
right tool.

HyperFrames animates through the
[frame-adapter](/concepts/frame-adapters) pattern. Any runtime that can answer
"what should the screen look like at frame N?" plugs in and renders
deterministically. [GSAP](/guides/gsap-animation) is the default adapter and
covers most motion, so you rarely need to name it. The cases below are the ones
where the default can go wrong. There, the prompt should pick the runtime.

## Real 3D → Three.js via the adapter

This is the one pin to state every time. Ask for Three.js explicitly for
anything with genuine **depth, lighting, or a camera** — a rotating product, a
scene you move through, surfaces that catch light:

> 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`

<DocsVideo
  title="HyperFrames video: Example 3d Cards"
  src="https://static.heygen.ai/hyperframes-oss/docs/images/prompting/example-3d-cards.mp4#t=0.1"
  loop
/>
*The Three.js version of the isometric-cards prompt — real shadows and lighting, one-shot.*

The engine rationale is simple. CSS `perspective` transforms skew flat planes.
There is no light source and no camera, only projected rectangles, so they read
flat the moment lighting or parallax matters.

Three.js is a first-party seek-safe runtime. The adapter publishes HyperFrames
time as `window.__hfThreeTime` and dispatches an `hf-seek` event on each seek, so
a real 3D scene renders frame-accurately like everything else.

Treat "real 3D" as "Three.js." This is a validated default, not a preference.
The exception is when you specifically want a flat, stylized fake-3D look.

Camera moves are part of the same rule. A drone orbit, a dolly, or a push-in
only exists where there's an actual camera:

<DocsVideo
  title="HyperFrames video: Camera Orbit"
  src="https://static.heygen.ai/hyperframes-oss/docs/images/prompting/camera-orbit.mp4#t=0.1"
  loop
/>
*A seek-driven Three.js drone orbit. The camera sweeps a continuous arc, which CSS transforms cannot do.*

- ❌ `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

You may 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. It's already the default. Don't
name a runtime here. Describe the motion instead. See [Motion that reads
premium](/prompting/motion):

> The headline slides up per word, staggered 0.1s apart, easing out as it lands.

CSS keyframes and the Web Animations API are supported adapters too. Name them
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.

An SVG "line draws itself" effect (animated `strokeDasharray` /
`strokeDashoffset`) is also GSAP-default territory. See the appendix's [SVG
draw-on rows](/prompting/rules-and-anti-patterns#svg-draw-on) for two lint
gotchas worth knowing before you ask for one.

## 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](/prompting/transitions) for the
vocabulary.

## Determinism surfaces in the prompt

Every runtime renders under the same [determinism](/concepts/determinism)
contract. The frame clock is `t = frame / fps`. There is **no wall clock, no live
network at render time, and no unseeded randomness**.

Two asks bump into this, so phrase them accordingly.

Live data can't be fetched at render time, because the render must be
reproducible:

- ❌ `fetch the current BTC price and count up to it`
- ✅ `count up to $67,400` with a fixed value baked in, or `read the target from a variable I pass at render time`

Unseeded randomness renders differently each frame and breaks reproducibility:

- ❌ `scatter 200 particles randomly`
- ✅ `scatter 200 particles from a seeded random layout` — say **seeded** and the positions stay stable across frames and re-renders

The rule of thumb: anything the video needs to *know* must be present before
rendering starts, baked in or passed as a
[variable](/prompting/variables-and-templating). Anything random must be seeded.

## The capstone thread

<Note>
**Capstone thread** — the [Level 7 film](/prompting/capstone)'s Depth region is
real Three.js through the frame adapter. The timeline wire coils around a rim-lit
faceted form, and the protagonist chip threads the coil's loops and passes behind
the form with true depth occlusion (cut from the film, below).
</Note>

This is the clause in the [full capstone
prompt](/prompting/capstone#the-prompt-word-for-word) that buys the piece. It's
prompt language you can lift for your own video:

> **Depth (52–56s).** The wire spirals off the flat plane into real 3D — a **Three.js scene via the frame adapter** (never CSS fake-3D): the camera descends following the wire as it coils around a rim-lit faceted form (ink material on charcoal), mono axis readouts landing on cue, then rises back to the plane with the wire leading the way out. The coil winds up out of the wire and collapses back onto it — its ends never float cut off in mid-air — and the protagonist chip joins the 3D scene for the crossing: it rides the wire straight through the coil's loops and passes behind the form with true depth occlusion, never floating over the geometry as a flat overlay.

<DocsVideo
  title="HyperFrames video: Capstone Region Depth"
  src="https://static.heygen.ai/hyperframes-oss/docs/images/prompting/capstone-region-depth.mp4#t=0.1"
  loop
/>
*That clause, rendered — the region cut from the finished film.*

*Next: [Media and audio](/prompting/media-and-audio) — precise phrasing for
voiceover, music, sound, and assets, instead of motion and rendering.*

## Related topics

- [Frame adapters](/concepts/frame-adapters) — the seek-by-frame contract and the full list of supported runtimes
- [Deterministic Rendering](/concepts/determinism) — why no live data and no unseeded randomness
- [Motion that reads premium](/prompting/motion) — describing everyday GSAP motion so it doesn't read as cheap
- [Transitions](/prompting/transitions) — naming the scene-to-scene handoffs worth a shader transition
- [Animate with GSAP](/guides/gsap-animation) — the default adapter in detail
