Re: Flexible, modular dia line decoration code

[Dave Hoover <spamless4 iasun2 epfl ch>]

Hi,

Here's some follow up info, and an EPS file showing more complete arrow 
results.  The arrow generating engine is pretty complete and quite 
general, and it appears stable.  The GUI (using properties), is hardly 
modular for the time being, but the arrow engine code is written to 
permit this easily.  I've attached the code to Bug ID 98593 if somebody 
wants to try it out.

The GUI just calls functions to create a few home-made arrows, allowing 
the user to specify only one (symmetry) of the many arrow options.

The GUI does NOT allow one to superimpose several different 
user-specified arrow heads, and many arrow specifications can not be 
specified with the gui.  But this may give you an idea what is possible 
with more general code.  I agree that the color stuff is a bit kitchy, 
but hey, it came along for free.

Lines are drawn with round caps so that intersections of wide lines 
won't look bad. The code, however, allows dia standard arrows to be used 
as decorations, which should result in modular code that could use 
sharp-tipped arrows as components.

Most of the new arrow code is in the bondgraph library for now.  There 
is a  'MTT Bond' object that uses this arrow code (click on the 
causality options, to see).  But this object is not very interesting 
from a arrow point of view.  There is another line object that I used to 
draw the attached diagram.

See my previous post for more info about these arrows, and the 
ORIENTATION property, and how this works.  The principle addition is a 
'Repeat' structure which defines a transformation affecting angle, 
color, and placement-defining gaps.  Given a DecorationProp (which 
defines a simple decoration), a Repeat structure can be used iterate on 
the DecorationProp, transforming it with each iteration, generating a 
GList of DecorationProps.  Both the DecorationProp and the Repeat 
structure are general enough to allow almost any kind of arrow, and also 
to allow any dimension to be a fixed length, a general function of line 
width, proportional to visible line length, or some combination of these.

As usual, these files are copyrighted (2002) by David Hoover, and you 
can use and copy the stuff according to the GNU General Public License 
(GPL) as distributed with dia, and found on http://www.gnu.org.

Dave.

gallery.dia.gz

gallery.eps.gz