SKP version map (SketchUp 2017 to 2020)

Straight after the header comes the first object of the MFC archive, a CVersionMap. It lists every class the model may contain and the version of that class’s layout in this file, and ends with the name End-Of-Version-Map. The map is how SketchUp knows how each object after it is laid out. In this format it is also what marks the file as SketchUp 2017 or later: CEntity is at version 5. All numbers are little-endian.

00000054  FF FF 00 00 0B 00 43 56 65 72 73 69 6F 6E 4D 61 70 FF FE FF …

The class record of the version map after a twelve-character version, such as {18.0.16975}, followed by the first entry’s string

Layout

Part	Bytes	Meaning
Class record	17	`FF FF 00 00 0B 00` and `CVersionMap`: a new class, schema 0.
Entries	varies	One a class: a CString class name and a u32 version.
End	44	The CString `End-Of-Version-Map` and a u32 0.

Class record

The map is an object, so it starts the way MFC starts the first object of a class: with a new class record (see class tags).

Offset	Size	Type	Name	Meaning
0	2	u16	Tag	`FFFF`, MFC’s new class tag: a class description follows.
2	2	u16	Schema	The class’s schema number, its layout version as MFC sees it: 0.
4	2	u16	Name length	The length of the class name in bytes: 11.
6	11	ASCII	Class name	`CVersionMap`.

These 17 bytes are the same in every file seen. They start at 0x50 after a ten-character version such as {17.1.174}, and at 0x54 after a twelve-character one.

Entries

Each entry names a class and gives its version:

Offset	Size	Type	Name	Meaning
0	4 + 2 × length	CString	Class	The class name, such as `CFace`.
then	4	u32	Version	The version of that class’s layout in this file.

The entries are in alphabetical order in every file seen. One entry, for the class CArcCurve at version 3:

FF FE FF 09 43 00 41 00 72 00 63 00 43 00 75 00 72 00 76 00 65 00 03 00 00 00

The marker, the length 9, “CArcCurve” in UTF-16LE and the version 3

Class names

The class names are CStrings in the same form as every other string in the file: the marker FF FE FF, a length in characters (one byte for names this short) and the name in UTF-16LE (see Strings). The name in the class record before them, by contrast, is MFC’s own class name in ASCII.

End of the map

The last entry has the name End-Of-Version-Map (18 characters, 12 hex) and the version 0:

FF FE FF 12 45 00 6E 00 64 00 2D 00 4F 00 66 00 2D 00 56 00
65 00 72 00 73 00 69 00 6F 00 6E 00 2D 00 4D 00 61 00 70 00 00 00 00 00

The entry that ends the map, 44 bytes

The model’s first fields follow straight after it.

Reading the map

Read the class record and check for FFFF, schema 0 and the name CVersionMap.
Read a CString, then a u32. Store the pair.
If the string was End-Of-Version-Map, stop: the map is complete. Otherwise go back to step 2.
Look up the version of each class before reading an object of it. For this format, CEntity is 5 or more.

Classes and their versions

The 2017 and 2018 files examined hold 58 classes each. These are the versions recorded from them, 47 classes in all; the others were not noted.

Class	SketchUp 2017	2018
`CArcCurve`	3	3
`CAttribute`	0	0
`CAttributeContainer`	0	0
`CAttributeNamed`	1	1
`CBackgroundImage`	10	10
`CCamera`	5	5
`CComponent`	11	11
`CComponentBehavior`	5	5
`CComponentDefinition`	10	11
`CComponentInstance`	5	6
`CCurve`	4	4
`CDib`	3	3
`CDimensionLinear`	6	6
`CDimensionStyle`	4	4
`CDrawingElement`	9	9
`CEdge`	2	2
`CEdgeUse`	1	1
`CEntity`	5	5
`CFace`	3	3
`CFaceTextureCoords`	4	4
`CGroup`	1	1
`CImage`	1	1
`CLayer`	2	2
`CLayerManager`	4	4
`CLoop`	1	1
`CMaterial`	12	12
`CMaterialManager`	4	4
`CPageList`	1	1
`CRenderingOptions`	36	37
`CSchemaFile`	1	1
`CSchemaFilterFile`	0	0
`CSchemaZipFile`	1	1
`CSectionPlane`	2	3
`CShadowInfo`	7	7
`CSkFont`	1	1
`CSketchUpModel`	26	28
`CSketchUpPage`	1	1
`CSkpStyle`	1	1
`CSkpStyleManager`	2	2
`CText`	9	9
`CTextStyle`	5	5
`CTexture`	6	6
`CThumbnail`	1	1
`CVertex`	0	0
`CViewPage`	12	12
`CWatermark`	1	1
`CWatermarkManager`	2	2

Two classes mark the start of this format: CEntity, the base of every entity, is at version 5 (it was 3 in SketchUp 2016), and CSketchUpModel at 26 (it was 25). SketchUp 2018 then raised CSketchUpModel, CComponentDefinition, CComponentInstance, CRenderingOptions and CSectionPlane, which may have changed their layouts. The parts this reference describes are the same in 2017 and 2018, so they are treated as one format until a file shows otherwise. No file from 2019 or 2020 was examined.

.SKP File Format – Version map