Img2scene

img2scene

Build a 3D object as a small tree of primitive parts that matches a reference image, scored by a deterministic critic until it passes, then emitted as flutter_scene Dart source.

The reference image is the acceptance criteria, not just inspiration. A deterministic comparator scores your render against it and returns tagged defects. Trust that verdict over your own impression, a model's self-score drifts upward while the comparator does not.

When this fits

Good for hard-surface and stylized props, boxy or geometric objects assembled from a handful of primitives (a mug, a crate, a little robot, a lamp, a mailbox, a game item). Weak at organic likeness, faces, characters, plants, cloth, anything that does not decompose into a few clean primitives. If the subject is organic, say so rather than forcing it.

The loop

1. Get an admissible reference

Either the user supplies a reference, or generate one from a text description using prompts/reference.md. An admissible reference is an isolated single subject on a clean flat background, roughly filling the frame, three-quarter front view, even lighting, no cast shadows on the background, square.

Gate it before using it.

dart run img2scene:admit <ref.png>

Fix or regenerate until it passes. A busy background, a cropped subject, or a dead-on/profile view all defeat the silhouette and scale metrics later, so a clean reference is worth the round trip.

2. Author a SceneSpec

Write a SceneSpec as JSON, a small tree of primitive parts. See references/example.md for a full worked spec and the field reference. In short, each part has a name, a primitive from the allowed kinds only, optional position/rotation(Euler degrees)/scale, an optional material (baseColor RGBA, metallic, roughness, emissive), and optional children. Set the camera (position, target, fovDegrees) to frame the subject the way the reference frames it.

Allowed primitive kinds, use these and nothing else: cuboid, sphere, icosphere, cylinder, cone, capsule, torus, plane, disc, ring, wedge.

Spend your effort on visual judgment, proportions, placement, color, and camera framing. Keep it a real decomposition. Every visible part of the reference should map to a part in the tree. A one-box spec for a detailed subject fails the shape gate.

3. Score it

dart run img2scene <spec.json> <ref.png>

The orchestrator renders the spec (through a headless flutter_scene integration test) and compares the render to the reference in one step. Read the verdict and the tagged defects.

4. Correct one thing at a time

Drive each edit from a defect, then re-score. Fix the blocking gates first, shape and scale, before the soft flags.

• scale_too_small grow the subject or move the camera in.
• scale_too_large shrink the subject or move the camera out.
• silhouette_mismatch the shape is wrong. Fix proportions, or add/remove parts.
• appearance_far (soft) tone, color, or coarse structure differ. Adjust materials and colors after shape and scale pass.
• low_edge_overlap (soft) internal detail or contours do not line up. Add or reposition detail parts after the gates pass.

A comparison passes when no blocking defect fires. Loop until it passes.

5. Emit the source

dart run img2scene:emit <spec.json>

This produces the flutter_scene Dart source for the passing spec. That source is the deliverable.

Reference commands

• dart run img2scene:admit <ref.png> gate a reference image.
• dart run img2scene <spec.json> <ref.png> render the spec and score it against the reference.
• dart run img2scene:compare <candidate.png> <ref.png> [--json] compare two images directly (lower-level, the orchestrator uses this internally).
• dart run img2scene:emit <spec.json> emit flutter_scene Dart source from a passing spec.