plotting directly using the renderer

Hi John, Martin, I was experimenting with drawing markers

    > one at a time for a ReadCursor class to provide the option
    > of marking the position of the cursor. I saw this email and
    > read the thread (the users mailing list is very helpful).

    > Since markers and lines go together and implementing
    > markers in the same way for ReadCursor would cause a lot of
    > code duplication, I tried pulling out the relevant
    > functions from and creating a Marker class -
    > attached. A test function is below. I am using TkAgg, so
    > _newstyle is True and renderer has draw_markers. x and y
    > in Marker.__init__ are sequences and are turned into 1d
    > arrays before passed to draw_markers. I get:

    > Traceback (most recent call last): File "",
    > line 9, in ? m.draw_marker(fcr) File
    > "/Users/dencheva/cvs-matplotlib/matplotlib/lib/matplotlib/",
    > line 556, in draw_marker markerFunc(renderer, gc, xt, yt)
    > File
    > "/Users/dencheva/cvs-matplotlib/matplotlib/lib/matplotlib/",
    > line 85, in _draw_pixel renderer.draw_markers(gc, path, xt,
    > yt) IndexError: Unexpected SeqBase<T> length.

With newstyle, the signature of draw_markers is

draw_markers(gc, path, rgbFace, x, y, trans)

where x and y are not transformed and trans is an mpl transform.

Here is the docstring from

    def _draw_markers(self, gc, path, rgbFace, x, y, trans):
        This method is currently underscore hidden because the
        draw_markers method is being used as a sentinel for newstyle
        backend drawing

        path - a matplotlib.agg.path_storage instance

        Draw the marker specified in path with graphics context gc at
        each of the locations in arrays x and y. trans is a
        matplotlib.transforms.Transformation instance used to
        transform x and y to display coords. It consists of an
        optional nonlinear component and an affine. You can access
        these two components as

        if transform.need_nonlinear():
          x,y = transform.nonlinear_only_numerix(x, y)
        # the a,b,c,d,tx,ty affine which transforms x and y
        vec6 = transform.as_vec6_val()
        ...backend dependent affine...

You may also want to search the dev archives for more elaborate
discussions. I'm short on time now so gotta run!