Re: [Pyx-user] colored symbols

[Andre W. <and...@ph...>]

Hi Gert,

On 03.06.03, Gert Ingold wrote:
> I want to draw colored symbols in a graph where the color of each symbol
> is determined via the datafile, i.e. I have a datafile consisting of three
> columns where the first column determines the x-value, the second column the
> y-value and the third value (between 0 and 1) the color. I tried to use
> a color palette but somehow I did not succeed. Is there a simple way to
> accomplish this task?

Unfortunately, the default symbol style does not (yet?!) provide
access to modify those stroke attributes by some additional data given
in a data file. Nevertheless, it is easy to implement such a feature
by creating a specialized subclass of the symbol class of the graph
module. By that, you have to write only a few lines:

    from pyx import *

    class mysymbol(graph.symbol):

        def __init__(self, palette, **args):
            self.palette = palette
            graph.symbol.__init__(self, **args)

        def othercolumnkey(self, key, index):
            if key == "color":
                self.colorindex = index
            else:
                graph.symbol.othercolumnkey(self, key, index)

        def _drawsymbol(self, g, x, y, point=None):
            self.symbolattrs.append(self.palette.getcolor(point[self.colorindex]))
            graph.symbol._drawsymbol(self, g, x, y, point)
            del self.symbolattrs[-1]

    g = graph.graphxy(width=10)
    g.plot(graph.data("test.dat", x=1, y=2, color=3), mysymbol(color.palette.Rainbow))
    g.writetofile("test")


The test.dat file should look like:

    0 0 0.0
    1 1 0.1
    2 2 0.2
    3 3 0.3
    4 4 0.4
    5 5 0.5
    6 6 0.6
    7 7 0.7
    8 8 0.8
    9 9 0.9
    10 10 1.0

I should mention, that a few features are lacking here which could be
added easily. Namely the iteration thru this style ends up with
instances of the parent class symbol and graph keys are poorly
supported (they will end up in regular symbols from the parent class).
Additionally I should add, that I consider the interfaces between
these components of the graph to be not at all stabilized. The are
not even documented yet. Hopefully things will get better in the
future ...


André

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