Legacy Container and Archive

This reference describes the pre-ZIP container used by SketchUp save targets 3–2020. It should be read with the legacy overview.

Header

All observed multi-byte scalars are little-endian unless noted otherwise.

product_name    legacy UTF-16 string, normally "SketchUp Model"
version_string  legacy UTF-16 string, for example "{8.0.1}"
model_id        16 raw bytes
saved_path      legacy UTF-16 string; may be empty
timestamp       u32 Unix timestamp
version_map     CVersionMap block
model_payload   serialized object graph

The saved path is informational. Consumers must not open it or use it to locate resources.

Legacy UTF-16 strings

Strings begin with ff fe ff, followed by a character count and UTF-16LE payload.

Form	Count encoding
Short	one-byte UTF-16 code-unit count
Extended	ff, then a little-endian u16 count
Large extended	extended u16 equals ffff, then a u32 count

The reader validates lengths before allocating or decoding. Both short and extended forms occur in compatibility samples.

Version map

The schema map precedes the object graph:

magic       ff ff 00 00
name_len    u16, observed 11
name        ASCII "CVersionMap"
entries     repeated legacy UTF-16 class name + u32 schema
sentinel    class name "End-Of-Version-Map"

The map belongs to the file and is authoritative for body selection. Class presence and schema numbers vary by save generation.

Object and class references

The graph maintains ordered class and object tables for the active archive session.

Encoded tag	Meaning in context
0x0000	Null object
0xffff	New class definition follows
`0x8000	index`
0x0001..0x7ffe	Short object back-reference
0x7fff + u32	Extended object/class reference; high bit selects class context

A new class definition carries schema: u16, name_length: u16, and the ASCII class name. The session allocates the object index separately; the raw class reference value is not an entity identity.

Skipping an unknown object-valued field would corrupt later references. The parser instead stops at the unsupported class/schema boundary.

Primitive values

Value	Wire representation
Boolean	archive boolean used by the owning schema
Point/vector	three f64 values
Plane	four f64 values
Transform	13 f64 values for legacy component placement
RGBA	four bytes; public colors normalize to ARGB where required
GUID	16 raw bytes
Typed option	one-byte type code followed by type-specific payload

Confirmed typed-option codes include 4 for a 32-bit integer, 6 for an f64, and 7 for a boolean. Strings, arrays, colors, times, points, vectors, unit vectors, and transforms also occur; unsupported types fail explicitly.

High-level root order

After End-Of-Version-Map, the stream is already inside the root model body; there is no separate root object tag. For SketchUp 8 the confirmed order is:

Order	Block
1	Version-gated model prologue and thumbnail state
2	Root component behavior and description
3	Options manager and model attribute dictionaries
4	Root camera and optional image data
5	Rendering options and version-gated state words
6	Root component: materials, layers, definitions, entities, relationships
7	Shadow/location, pages, axes, annotation styles, fonts, line styles, background image, styles, and watermarks

Later generations extend the tail according to the file’s schema map. Parsing uses explicit version branches rather than searching for byte signatures.

Options and attributes

The option manager has a version, a provider count, provider names, and name/value pairs terminated by an empty key. Attribute containers similarly hold named dictionaries with typed values.

Public mapping is owner-aware:

Archive owner	Public destination
Root model properties	Model.attribute_dictionaries
Definitions, materials, layers	Model.attribute_dictionaries_by_object_id
Scoped entities	Entities.attribute_dictionaries_by_entity_id

Archive container objects do not appear as duplicate public dictionaries.

Embedded image blocks

Legacy image data may appear in material textures, placed images, background images, watermarks, or thumbnail state. The containing class determines its meaning. Encoded PNG/JPEG bytes are preserved only when they belong to a public image-bearing object.

An observed thumbnail form contains an ASCII CDib key, stored schema, byte count, and encoded image bytes. Its stored schema may differ from the main version-map entry, so consumers must use the block’s own bounded envelope.

Safety requirements

• Validate every length against remaining bytes before reading.

• Bound recursion and retain one archive session per object graph.

• Never follow the serialized saved path.

• Do not infer class layouts from neighboring bytes.

• Report the file version, class, schema, reference index, and byte offset on failure.