threejs-core-scene-graph

add() preserves the object's local transform, so reparenting changes its world position and the object visually jumps. attach() recalculates the local transform to preserve the world position, keeping the object in place when moved to a new parent.

Call group.clear() to remove all children safely. Avoid forward for-loop removal, which skips elements due to index shifting; if selectively removing, iterate backwards or collect targets first then remove them.

matrixWorld is only recalculated during render or explicit updates, so reading it mid-frame returns stale values. Call updateWorldMatrix(true, false) before reading, or use getWorldPosition() which updates internally.

No. remove() and clear() only detach objects from the scene graph. You must explicitly call dispose() on geometries, materials, and textures to free GPU memory, and clear any Three.js objects stored in userData.

Layers are a 32-bit bitmask; objects render only when their layers overlap the camera's layers. Use layers.enable(n) to add a layer without removing others, since layers.set(n) replaces the entire bitmask with only that layer.

ShaderMaterial and RawShaderMaterial default to fog: false. You must set fog: true in the material options and manually include the fog shader chunks in your custom shader code for fog to apply.