RLE format specification

First line:

Newline delimiter may be [cr], [lf], or [cr][lf] due to different text-format standards for Mac, Unix, and Windows computers.

Following lines:

b: off (blank) o: on (live) $: end of line (note that 5$ is treated as five successive cr/lf) !: end of pattern and runlength is omitted if it = 1.

'[' and ']' are not actually in the text, of course.

Some database maintainers, notably Mark Niemiec, use 'x' and 'y' as alternatives to 'o' to denote different colors, to make distinct subpatterns easier to distinguish.

Newline characters are added as necessary to keep each line at 70 chars or less, and char sequences are never broken.

Any lines of text before the "x =" header line, or after the ! but before the next blank line, are generally considered to be comment text, not relevant to the interpretation of the RLE pattern itself. Comments may be placed either before or after the run-length-encoded pattern, but it's more common to put the comments at the beginning of the pattern (even though many Life programs, e.g., Life32 and MCell, write them at the end).

Comments before the header line are always prefixed at least with '#', almost always with '#C' or '#D', and predominantly with '#C ' or '#D ' (for "comment" and "description" respectively.) Comments after the closing '!' are generally not prefixed by anything.

Some programs (notably MCell, at least up to version 4.20) deal badly with comment lines over 70 characters long -- they may be truncated and/or interpreted as part of a pattern.

Ideally a program should simply ignore any initial lines starting with '#', unless it recognizes them as part of some program-specific extension. If a program wants to save the comments along with the pattern, that's fine.

However, occasionally parameter tags from XLife's much more versatile format will get mixed in with RLE comments, so it's worth mentioning these here. All XLife parameters begin with a '#' (and so are generally treated as comments by RLE decoders.)

Here is the list of Xlife tags, up to version 3.5/3.6, that might be found with RLE:

##

ignore the entire line

#M [x = xdiam , y = ydiam]

tag needed by Xlife 3.5 as a prefix to RLE header, to recognize RLE format.

#N

this line contains the internal name of the pattern

#O

This line contains information on the person who wrote the file format in the form: id "name"@machine date, for example: "Jon C. R. Bennett"@sushi.andrew.cmu.edu 1990-02-12 18:25:54

#C

this line contains a comment for the user

#r survivedigits/borndigits

Set new rules survivedigits and borndigits are a subset of digits out of the range 0 up to 8 counting the number of neighbours of the central cell

#L x y string

write the string (up to newline character) at the position (x,y)

#U filename

load a rule-set file [only in Eric Raymond's N-state mode]

#P x,y

starting coordinate for first 'picture-format' cell on following line (however, this has been implemented

#A

'absolute' x,y coordinates follow, separated by newlines

#R [xoff[yoff]]

'relative' x,y,coordinates follow, separated by newlines (i.e., relative to the mouse cursor, in contrast to a coordinate origin)

#D x,y

coordinate differences from the previous point, separated by newlines

#I patternname [xoffset[yoffset[rotate[flip[delay]]]]]

structured format for describing a large pattern in terms of subpatterns

#B name

Beginning of block containing the definition of a subpattern called name in a "library" file

#E

End of pattern block begun by the previous #B tag

The odd case is #D, which is also used in Life 1.05 format but means "description" in that context. Life32 automatically writes description tags containing ugly hexadecimal numbers that provide a checksum of sorts, for Life32's internal use in loading the pattern.

************** link to HK's extended RLE format description (for annotated patterns)? Here's the summary I have:**************

Each layer has an RLE-style header of the form

Picture format: