Claude
d4728061a9
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013TAaJBzbmePTECuv62BXYX
135 lines
5.9 KiB
Markdown
135 lines
5.9 KiB
Markdown
# Expressions, Rigging & MOGRT
|
||
|
||
After Effects is GUI software, so this delivers knowledge: ready-to-paste JavaScript expressions, rigging setups that make motion controllable, and template/export pipelines. Expressions read on the property they are pasted on; `value` is that property's keyframed/static value, `time` is the composition time in seconds, and `index`, `thisLayer`, `thisComp` are in scope.
|
||
|
||
For a deeper cookbook (tuned inertial bounce, every loop variant, advanced per-axis wiggle, `valueAtTime` echoes, `seedRandom` grids, full rigging walkthrough, Essential Graphics → MOGRT steps, Lottie/Bodymovin + Media Encoder presets), see `expression-library.md`.
|
||
|
||
## Core expressions
|
||
|
||
### Inertial bounce (overshoot after the last keyframe)
|
||
|
||
Paste on a Position, Scale, or Rotation property. It continues the velocity at the final keyframe into a damped sine — the classic "settle" motion.
|
||
|
||
```js
|
||
amp = 0.08; // overshoot amount
|
||
freq = 2.5; // oscillations per second
|
||
decay = 6.0; // how fast it settles
|
||
n = 0;
|
||
if (numKeys > 0) {
|
||
n = nearestKey(time).index;
|
||
if (key(n).time > time) n--;
|
||
}
|
||
if (n > 0) {
|
||
t = time - key(n).time;
|
||
v = velocityAtTime(key(n).time - 0.001);
|
||
value + v * (amp * Math.sin(freq * t * 2 * Math.PI) / Math.exp(decay * t));
|
||
} else {
|
||
value;
|
||
}
|
||
```
|
||
|
||
### Looping
|
||
|
||
```js
|
||
loopOut("cycle"); // repeat keyframed range forever
|
||
loopOut("pingpong"); // bounce back and forth
|
||
loopOut("offset"); // continue, accumulating (e.g. continuous travel)
|
||
loopOut("continue"); // extend final velocity linearly
|
||
loopOut("cycle", 2); // loop only the last 2 keyframes
|
||
loopIn("cycle"); // mirror, before the first keyframe
|
||
```
|
||
|
||
### Wiggle and stable randomness
|
||
|
||
```js
|
||
wiggle(2, 30); // 2 wiggles/sec, amplitude 30 (units match the property)
|
||
seedRandom(index, true); // unique-but-stable per layer; timeless=true
|
||
random(0, 100); // stable after seedRandom
|
||
wiggle(freq, amp, octaves=1, amp_mult=0.5, t=time); // full signature
|
||
```
|
||
|
||
`seedRandom(index, true)` before `random()` or `wiggle()` makes each layer differ but stay constant across renders — essential for grids of layers that must not flicker.
|
||
|
||
### Time remap & value-at-time
|
||
|
||
```js
|
||
// Sample another property/layer at a shifted time (echo/trailing motion)
|
||
delay = 0.2 * index;
|
||
thisComp.layer("Lead").transform.position.valueAtTime(time - delay);
|
||
|
||
// Speed up a precomp via time remap
|
||
linear(time, 0, thisComp.duration, 0, 6); // 6s source mapped over comp duration
|
||
```
|
||
|
||
## Rigging
|
||
|
||
Make motion controllable instead of hand-keyed:
|
||
|
||
1. Add a null/control layer (often a "Controls" layer). Add **Slider Control**, **Checkbox Control**, **Color Control**, **Angle Control**, or **Point Control** effects to it.
|
||
2. Reference them with the pick-whip or by path:
|
||
|
||
```js
|
||
ctrl = thisComp.layer("Controls");
|
||
amt = ctrl.effect("Intensity")("Slider"); // Slider Control → ADBE Slider Control-0001
|
||
on = ctrl.effect("Enable")("Checkbox"); // Checkbox: 1 or 0
|
||
col = ctrl.effect("Tint")("Color");
|
||
|
||
if (on == 1) value * amt else value;
|
||
```
|
||
|
||
3. Parent transforms to a null so one move drives many layers. Use `toComp`/`fromComp` to convert coordinate spaces when layers are parented or in different comps.
|
||
|
||
```js
|
||
// Stagger N layers off one master slider
|
||
master = thisComp.layer("Controls").effect("Reveal")("Slider");
|
||
delay = 4 * index; // 4 frames per layer
|
||
master.valueAtTime(time - framesToTime(delay));
|
||
```
|
||
|
||
## Essential Graphics / MOGRT
|
||
|
||
1. Open **Window → Essential Graphics**, pick the comp as the Master.
|
||
2. Drag the Slider/Checkbox/Color/Text source properties into the panel to expose them.
|
||
3. Group, rename, and set comment fields for editors.
|
||
4. **Export Motion Graphics Template** → a `.mogrt` usable in Premiere Pro / AE. Keep driving expressions referencing the exposed controls so editors change only the exposed params.
|
||
|
||
Set "Allow fonts to substitute" off and embed/package fonts where possible so the template renders consistently elsewhere.
|
||
|
||
## Export from expressions/template work
|
||
|
||
### To Lottie (Bodymovin / `@lottiefiles/bodymovin`)
|
||
|
||
- Stick to Lottie-supported features: shape layers, transforms, masks, track mattes, basic expressions converted to keyframes.
|
||
- Avoid blur-heavy effects, blend modes, 3D layers, and most native effects — they don't translate.
|
||
- Bake expressions to keyframes if the renderer is strict, or use the `expressions` flag in Bodymovin and test on the target player (web/iOS/Android renderers differ).
|
||
- Run **Bodymovin → Render** to produce `data.json` (+ optional images). Verify in a Lottie preview before handoff.
|
||
|
||
### To video (Media Encoder)
|
||
|
||
- **File → Export → Add to Adobe Media Encoder Queue** (or render queue for AE-native).
|
||
- Delivery: **H.264** (MP4), bitrate ~10–20 Mbps for 1080p, VBR 2-pass.
|
||
- Master/intermediate: **ProRes 422 HQ** (or ProRes 4444 when alpha is needed).
|
||
- Transparency: ProRes 4444 or PNG/QuickTime with an alpha channel; H.264 cannot carry alpha. (See `export-recipes.md` for the full codec/alpha/bitrate matrix.)
|
||
|
||
## Quick reference
|
||
|
||
| Goal | Expression |
|
||
|---|---|
|
||
| Loop keyframes | `loopOut("cycle")` |
|
||
| Continuous travel | `loopOut("offset")` |
|
||
| Subtle life | `wiggle(2, 20)` |
|
||
| Stable per-layer random | `seedRandom(index,true); random(...)` |
|
||
| Settle/overshoot | inertial bounce (above) |
|
||
| Echo another layer | `valueAtTime(time - delay)` |
|
||
| Read a slider | `effect("Name")("Slider")` |
|
||
| Frames ↔ seconds | `framesToTime(n)` / `timeToFrames(t)` |
|
||
|
||
## Gotchas
|
||
|
||
- An expression overrides keyframes on that property unless it incorporates `value`; start most expressions from `value`.
|
||
- `index` is the layer's stacking number — it changes if layers are reordered; prefer named lookups for stable rigs.
|
||
- Expression errors disable the expression and show a yellow banner; check the property's path names (effect names must match exactly, including duplicates' suffixes).
|
||
- Pre-compose for reuse; name layers; use shy/lock and guide layers for safe areas before handoff.
|
||
</content>
|
||
</invoke>
|