Jan 22 2011

My comments on the LDraw file format spec

Category: LDraw,Lego,SoftwareSpiller @ 17:47

As I’m planning on writing a LDraw parser and viewer I read the LDraw.org File Format Version 1.0.0. However I find it rather vague so I’m sharing my comments on it.

Section LDraw Files:

“All LDraw files are plain text based. A specific character set encoding (UTF-8, ISO-LATIN1, US-ASCII7, etc) is not defined and software authors are free to use whatever encoding is appropriate for their target platform(s).”

I really don’t think it is a good idea not to specify any restrains on the character encoding. Just imagine a parser expecting ISO-LATIN1 getting a file encoding in UTF-16… But a file encoded in UTF-8 with BOM can be enough to cause parsing errors. My suggestion would be to enforce ASCII (8-bit) compatible character encodings and recommend UTF-8 (without BOM) if ASCII isn’t sufficient. What about newlines? For better “cross-platform portability” it should be defined which ways of defining newlines are allowed (in order to make sure parsers support them). Because if the parser doesn’t detect the newlines properly, it can’t read the file at all…

The whitespace characters allowed for keyword and parameter separation include spaces and tabs.

Include? Does this mean that other whitespace characters are allowed?

Section “Line Types“:

When describing the format (for example “0 !<META command> <additional parameters>”) spaces are used for separating keywords/parameters. I guess this means one or more whitespace characters?

Sub-section “Line Type 0“:

“0 // <comment>”, whitespace is required between “//” and the comment? (I guess I’m just not used to having whitespace there…) “<META command> is any string in all caps”, may there appear whitespace in the command? In an example in “Adding New META Commands” there is: “0 !LDPARSER EXAMPLE”, however I prefer that whitespace is not allowed as it makes separating the command from the parameters easier.

Sub-section “Line Type 1“:

For the file parameter there are several directories included, in which order should these be checked (in case of identical filenames)?

Section “META Commands“:

Many of the original commands are described by how they affect the original LDraw program and in my opinion this doesn’t belong in a spec for the file format. It should focus on the intended purpose instead of describing an implementation. The “LDraw.org Official Library Header Specification” seems to describe how to describe a file with meta-commands in order to include it in the official library, it doesn’t really specify the commands. Yet this document is the only documentation for several commands… On a side note, “0 Name: Filename.dat” and “0 Author: RealName [UserName]” are both not written in uppercase entirely and include a ‘:’ before the whitespace though this isn’t included in “List of Official META Commands”? According to the spec it can surely not be a META command since it isn’t in uppercase, but the LDraw team apparently treats it like that anyway?

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