Re: [PyX-user] A general symbol attr?

[Armin S. <li...@ar...>]

Hallo,

> Note that usually in PyX, attributes come in lists, so the PyX-way of
> doing this would be
>
>  point(x, y, [symbol.cross])
>
> Then you could also allow things like
>
>  point(x, y, [color.rgb.red, symbol.cross])

This was really what my first attempt looked like, but then I thought that=
=20
e.g. the color should be an attribute of the symbol. What I had in mind was=
=20
the idea of using symbol in other places, too, e.g.
  line(x1, y1, x2, y2, [rgb.red, symbol.cross([rgb.blue])]).
Just taking the symbol as a parameter and not a list of attributes is model=
led=20
after the usage of the style parameter in plot(). I defined symbol as an=20
attribute (in contrast to a graph style) though, because of possible future=
=20
usecases.

> They are stored as attributes x_pt and y_pt, that is, in PS points.

Ah, so I can access e.g. the vertices of a rect via the pathitems and x_pt,=
=20
y_pt. Nice to know. Thanks!

> However, "edges of a path" may not be a very well defined concept. I
> could imagine something like the first and last point of a line and the
> first and last points of a B=E9zier curve. If you want to use that, just
> convert the path in a normpath and use that instead.

I'm sorry. s/edges/vertices/. I missed this one. The idea was to have a=20
decorator that could emphasize e.g. the vertices of a triangle.

> But your idea is still interesting. We could have something like:
>
>   c.stroke(path.point(x, y), [deco.symbol.cross])
>
> where point is a degenerate line:
>
> class point(line):
>     def __init__(x, y):
>         line.__init__(x, y, x, y)
>
> The advantage would be that one decouples the position x, y from the
> rest of the symbol. One would have to think about the implications when
> stroking/filling such an object, though.

I like this idea. And it would fit into the concept of symbol.cross drawing=
 a=20
cross at each vertex of a general path.

> An alternative solution without this problem would be to put the symbol
> in the path (future: paths) module and have something like
>
>   c.stroke(path.cross(x, y, size=3D3), [color.rgb.red])
>
> Then, the separation between the position and the rest of the attributes
> is drawn differently.
>
> Of course, we could also have a combination between both ways, with the
> second way (via path(s)) being the more fundamental one.

I don't know if a path.cross or a path.diamond would be of much use besides=
=20
representing a point. But it may be worth some thoughts...

Cheers
=2D-=20
Armin Straub