Thanks Dave
I was not clear enough, -Head can have values; both, all, begin, end, whereas Q can be 0, 1, 2, 3, so some go-between is required.
I finally looked and found part of it in source file thline.h
// tags pre arrow
TT_LINE_TAG_HEAD_BEGIN = 1,
TT_LINE_TAG_HEAD_END = 2,
Presumably somewhere else NONE is set to or implied as zero and BOTH is set to BEGIN + END.
That would complete the mapping from the data type that -Head takes as input in a th2 file, to the 0, 1, 2 or 3 that ‘line arrow’ requires for variable Q.
I rather suspect I don’t have the requisite knowledge for this, but sometimes I feel the need to push the boundaries anyway!
:)
Bruce
From: Therion <therion-bounces@speleo.sk> On Behalf Of Dave Clucas via Therion
Sent: Saturday, 31 March 2018 2:28 PM
To: therion@speleo.sk
Cc: Dave Clucas <dave.clucas@icloud.com>
Subject: Re: [Therion] scaling line ornamentation - metapost (Bruce Mutton)
I’m not sure about this but I suspect that it doesn’t involve parsing. It’s likely that the metapost expects a parameter or parameters to be passed to it which it then assigns to the variable Q in its own procedure. It won’t care what the calling program calls it. I think the arrowhead is probably defined within an arrow class (arrow.h perhaps).