CMX file format: Corel Presentation Exchange

Corel Presentation Exchange is Corel’s format for passing a drawing to other programs. A .cmx file is a RIFF file like a CorelDRAW drawing, but it holds a list of drawing instructions rather than objects, and it is a different format with different chunks. CorelDRAW 6 and later also save one inside the drawing, in a chunk called cmx1, and full-colour pattern fills (vpat) are CMX files too. This page follows libcdr’s reader (its CMXParser), which the Document Liberation Project wrote from files, as nothing is published. The tagged data inside an instruction is not described here; libcdr reads only some of the instructions.

The file

It starts RIFF, a 32-bit length and the form type CMX1. libcdr accepts RIFX, the big-endian form, and a form type of any case that starts “CMX”; the byte order is also given in the header. The chunks seen in a real file, the one in the CorelDRAW 6 drawing MP3_CD.CDR, are these:

Chunk	Times	Holds
`cont`	1	The header, 180 bytes.
`ccmm`	1	72 bytes, not read by libcdr.
`page`	6	A page: a list of instructions.
`rlst`	6	40 bytes after each page, not read by libcdr.
`rfnt`	1	The font description section.
`rotl`, `rott`, `rpen`, `rdot`, `rota`	1 each	Description sections: outlines, line styles, pens, dot-dash patterns, arrowheads.
`rclr`	1	The colour description section: a 16-bit count and the colours.
`rscr`	1	The screen description section.
`LIST indx`	1	The index: `ixlr` (a page’s layers, one per page), `ixtl` (index tables), `ixpg` (the pages) and `ixmr` (the master index).
`LIST INFO`	1	Keywords (`IKEY`) and a comment (`ICMT`).

A file can also hold a DISP thumbnail (its header offset says where; the file above has none) and, for bitmaps, LIST imag lists of an info chunk and a data chunk.

cont: the header

Offset	Size	Field	In MP3_CD.CDR
0	32	File identifier, text	`{Corel Binary Meta File}`
32	16	Platform, text	`Windows 3.1`
48	4	Byte order, text: `2` little-endian, `4` big-endian	`2`
52	2	Coordinate size, text: `2` or `4` bytes	`4`
54	4	Major version, text	`2`
58	4	Minor version, text	`0`
62	2	Base units, a code	35 (0x23)
64	8	Units scale, a double: metres a unit	1e-7
72	12	Unknown	zeros
84	4	Index section offset, from the start of the file	0xCFF6, the `ixmr` chunk
88	4	Info section offset	0xD04C, the `LIST INFO`
92	4	Thumbnail offset; 0xFFFFFFFF none	0xFFFFFFFF
96	4 coordinates	Bounding box	–1,234,567; 617,411; 2,355,310; –881,889
112	68	Unknown	one non-zero field, 453, then zeros

The coordinate size, 2 or 4 bytes, decides the width of every coordinate in the file and how the tagged data inside the instructions is laid out (a 16-bit file has no tags).

The index

ixmr: the master index

Field	Size	Description
Master id	2
Size	2
Number of records	2	n.
Records	n × 6	A section type (2) and its offset from the start of the file (4).

Type	Section	Type	Section
1	master index table	16	line style descriptions
2	page index table	17	arrowhead descriptions
3	master layer table	18	screen descriptions
4	procedure index table	19	pen descriptions
5	bitmap index table	20	dot-dash descriptions
6	arrow index table	21	colour descriptions
7	font index table	22	colour correction
8	embedded file index table	23	preview box
10	thumbnail	15	outline descriptions

ixpg: the page index

A 16-bit count of pages; then for each page, in a file of 32-bit coordinates, its size in the file (2 bytes, at least 16), then four 32-bit offsets: the page, its layer table, its thumbnail and its reference list. libcdr reads each page offset once.

page and proc: instructions

A page chunk (or a procedure, proc) is a series of instructions. Each starts with its size as a signed 16-bit number (a negative one means a 32-bit size follows), then a signed 16-bit code, whose absolute value names the instruction; the data follows up to the size. In a 32-bit file the data is a series of tags: a tag byte, a length and the tag’s data, ending in the tag 0xFF.

Code	Instruction	Code	Instruction	Code	Instruction
2	Comment	66	Ellipse	93	SetGlobalTransfo
9	BeginPage	67	PolyCurve	94	AddGlobalTransform
10	EndPage	68	Rectangle	95	RestoreLastGlobalTransfo
11	BeginLayer	69	DrawImage	98	TextFrame
12	EndLayer	70	BeginTextObject	99	BeginParagraph
13	BeginGroup	71	EndTextObject	100	EndParagraph
14	EndGroup	72	BeginTextGroup	101	CharInfo
17	BeginProcedure	73	EndTextGroup	102	Characters
18	EndSection	85	SetCharStyle	103	PushTint
20	BeginTextStream	86	SimpleWideText	104	PopTint
21	EndTextStream	88	AddClippingRegion	111	JumpAbsolute
22	BeginEmbedded	89	RemoveLastClippingRegion
23	EndEmbedded	90	ClearClipping
65	DrawChars	91, 92	PushMappingMode, PopMappingMode

libcdr draws the instructions BeginPage, BeginLayer, BeginGroup, PolyCurve, Ellipse, Rectangle, DrawImage and JumpAbsolute; it skips the others by their size. The tags of the ones it reads (rendering attributes with fills, outlines and lenses, point lists, boxes) are not described on this page.

In a drawing

A CorelDRAW 6 drawing has a cmx1 chunk whose data is a whole CMX file, starting RIFF. In MP3_CD.CDR it is 53,416 bytes with six page chunks, one for each page of the drawing. The explorer offers it as a file of its own.

In the explorer

A CMX file opens with its chunks, the header and the index field by field, and each page as a list of instructions named by their codes. The instructions are not drawn and their tagged data, the description sections (rclr, rpen and the others) and a big-endian (RIFX) file are not decoded.

CPX and other names

The format is named Corel Presentation Exchange. Files called .cpx and .cdrx, which are sometimes linked with CorelDRAW, were not found in any source this page follows and no sample could be had, so nothing is claimed about them; the one .cpx on the machine this was written on (a Windows for Workgroups file) is something else. The explorer opens .cmx files that start like a CMX file; other files that happen to be called .cmx (the Fuchsia component manifests, for one, are JSON) are not CMX and show as what they are.

.CMX File Format