drawing, config, callbacks: add arrowtype option allowing arrow heads…

[pascal-niklaus]

… at both line ends

Syntax in config file with new option arrowtype, which can take values "->" (default), "<-", or "<->".

Example:

"red Pen" = PEN (size=5 color="red", arrowsize=2, arrowtype="->");
"blue Pen" = PEN (color="cyan", size=2, arrowsize=2 arroytype="<->");
"yellow Pen" = LINE (color="yellow" size=2 arrowsize=2 arrowtype="<-");

[bk138]

Again, sorry for the long delay, I got held back by other stuff. Also again, thanks for that nice contribution, I have only some minor change requests.

PS: Don't bother keeping a clean history on the branch, I'll simply squash-merge when ready.

Thanks again!

[pascal-niklaus]

I updated the PR accordingly, now writing the value in the enum as

  GROMIT_ARROW_DOUBLE = (GROMIT_ARROW_START | GROMIT_ARROW_END )

which should be clear...

[bk138]

I updated the PR accordingly, now writing the value in the enum as

  GROMIT_ARROW_DOUBLE = (GROMIT_ARROW_START | GROMIT_ARROW_END )

which should be clear...

Yeah this is even more clear, thanks!

[bk138]

One more thing: I noticed that the following minimal config

"red Pen" = PEN (size=5 color="red" arrowtype="double" arrowsize=3);
"default" = "red Pen";

does not correctly parse arrowtype.

[pascal-niklaus]

One more thing: I noticed that the following minimal config

"red Pen" = PEN (size=5 color="red" arrowtype="double" arrowsize=3);
"default" = "red Pen";

does not correctly parse arrowtype.

Indeed parsing arrowsize did reset the option to arrowtype=="end", so arrowtype only worked as intended after arrowsize.

Also, I removed ARROW_TYPE_NONE because it was redundant with arrowsize==0. Anyway, arrowsize==0 acts as flag whether there are arrows, and only then is the arrow type tested.