Rotating chart axis labels

[John Darrington]

I'm trying to further improve the appearance of histograms and other
charts.  One of the problems we still have is the x-axis labels clashing
with one another.

I think a good solution would be to have them orientated at 45 deg when there
are lots of bins.  This is  what other software does
 (http://www.tulane.edu/~panda2/Analysis2/one-way/histog1.jpg)

Pango/Cairo makes it quite easy to do this.  But I'm not sure how it would fit
in with our existing code.  For example xrchart_label in 
src/output/cairo-chart.c
looks like:

void xrchart_label (cairo_t *, int horz_justify, int vert_justify,
                    double font_size, const char *);

How do we express rotated text in terms of horizontal and vertical 
justification?
Maybe  we should generalize this interface?

Ideas?

J'

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