Lottie import

anim import-lottie INPUT.json -o OUTPUT.anim converts a deliberately bounded Lottie profile into ordinary, editable Anim source. The output has no runtime dependency on Lottie and is deterministic: importing the same bytes produces the same source bytes.

The implemented profile covers the constructs exercised by examples/RRX9U6XiOf.json: two-dimensional shape and precomposition layers, cubic paths and compatible path morphs, solid fills and strokes, group and layer transforms, arbitrary rotation, exact temporal easing, spatial motion tangents, parenting, layer timing, opacity, normal compositing, and alpha track mattes. Unsupported input fails with a JSON path rather than producing a partial approximation.

The byte-exact generated fixture is committed as examples/lets-go.anim.

The bounded profile requires a zero composition in-point, unit layer stretch, nonnegative layer start offsets, visible 2D layers and shape items, and expression-free properties. These constraints are checked rather than silently ignored.

Why core changes were required

The source converter is intentionally thin. It maps Lottie concepts onto general Anim capabilities added in Specs 0039–0041:

Lottie construct	Native Anim representation
cubic shape and morph	retained BezierPath plus Signal<Path>
solid fill/stroke	retained path paint with fill rule, cap, join, and miter
arbitrary rotation	sampled Q16 affine transform
multi-keyframe properties	typed keyframes signals
spatial to/ti tangents	cubic Signal<Point2> consumed by place
alpha track matte	retained mask scene
precomp start offset	exact sequence local time

These are reusable language and engine features; none contains fixture names, layer indices, or path coordinates.

Common constructs still requiring engine work

The importer rejects the following popular Lottie features because faithful support needs a meaningful retained-engine extension, not a JSON-only rewrite:

Construct	Required Anim extension
linear/radial gradients	retained brush/shader values and deterministic CPU/SVG paint
trim paths, dash offset, taper	retained path-measure and stroke-effect semantics
merge paths and repeaters	bounded retained path boolean/instance operators
subtract/intersect/inverted/feathered masks	mask modes plus deterministic blur coverage
non-normal blend modes	explicit linear-light compositing operators
text layers	pinned font assets, shaping, glyph fallback, and text-on-path rules
image layers	bounded asset references, decoding, color management, and sampling
expressions	a specified deterministic expression language or translation boundary
3D layers, cameras, and lights	projective transforms, depth ordering, and 3D rendering
effects	a typed, bounded image-effect graph with backend parity
negative start offsets and non-unit time stretch	a retained local-time transform

The error boundary is part of the compatibility contract. Adding any row should be a separate vertical slice with scene semantics, language exposure, CPU rendering, SVG behavior where applicable, and conformance fixtures.

Conformance evidence

The committed fixture was independently rendered with lottie-web 5.13.0's SVG backend. Both reference SVG and Anim SVG were rasterized by the same FFmpeg SVG decoder at 1000×800 before comparison:

Frame	SSIM	PSNR
0	0.999987	60.765 dB
90	0.994310	30.530 dB
180	0.999938	54.851 dB

The comparison permits subpixel and easing-grid differences; the native Anim determinism contract remains byte-exact and is tested separately.

Lossy Soccer compatibility edition

examples/soccer-supported.json is a hand-translated, explicitly lossy version of examples/soccer.json. It demonstrates how a complex export can be reduced to the existing profile without weakening the importer's fail-closed default. The original source remains unchanged.

The compatibility edition retains the main 330-frame shot at 1440×1024 and 60 fps. It preserves ordinary cubic path animation, supported transforms, parenting, solid painting, and layer timing. Ellipses are converted to cubic paths, gradients to deterministic midpoint colors, and the matte-only ball artwork to a classic outlined pentagon-and-seam motif. Its seven-shade skin palette is hand recolored from pink to warm light brown while retaining the original shading. Four unsupported finger fragments are replaced by one overlapping hand silhouette.

The translation deliberately omits alternate shots, effects, blend modes, matte-dependent artwork, boolean/path modifiers, hidden construction layers, and unsupported local-time behavior. It is a showcase of graceful degradation, not a conformance result or a replacement for the missing engine features.

Convert and render a representative SVG frame:

anim import-lottie examples/soccer-supported.json \
  -o /tmp/soccer-supported.anim
anim render \
  /tmp/soccer-supported.anim --frame 200 \
  -o /tmp/soccer-supported-200.svg --force

The regression test imports the complete compatibility file and proves that frames 100, 200, and 300 produce distinct native SVG scenes.