Re: logarithmic axis/grids

[Fabian Foerg <fabian foerg gmx de>]

Roland Bock wrote:
> Dear Brian,
>
> thank you for the roses and sorry for letting you wait so long, but I
> was in the middle of another project.
>
> In principle, introducing logarithmic scales and grids should be fairly
> easy to do: There is a struct called GtkDataboxCanvas which contains the
> necessary information for positioning graph elements (dots, lines, etc)
> on the screen. Up to now, the real calculation is done in the individual
> graph classes, though. This calculation could be centralized (simple).
> Then it would be easy to replace the linear transformation by a
> logarithmic one.
>
> Of course, similar actions are necessary for functions like
> gtk_databox_value_from_coord and maybe (I haven't put too much thought
> into that yet) also for scrollbars.
>
> I am going to try to do this soon. There should be no implications for
> anybody who wants to stick with the linear scales.
>
>
> The rulers are different, though, because we are using the standard gtk
> rulers and I don't think they can be switched to non-linear scales.
> Maybe the nxpruler library suggested by Fabian can help here
> (http://numexp.org)? I haven't looked into that.
>
>
> Regards,
>
> Roland


Yes, with the nxpruler library from gnumexp-0.11.0 (http://numexp.org/) 
you can create logarithmic scale rulers.
My program cournol (http://cournol.k-2007.de/) uses a modified version 
of gtkdatabox which makes use of these nxprulers.
The patch which adds nxpruler support to gtkdatabox is in the cournol 
sources under patches/gtkdatabox.diff.
The nxpruler library is also in the cournol sources under lib/nxpruler.
In cournol, the nxprulers are not set to logarithmic mode.
To get the logarithmic mode you would add the line 
"nxp_ruler_set_mode(NXP_RULER(ruler), NXP_RULER_LOG);" where it is 
appropriate.
Look at lib/nxpruler/test.c in gnumexp for examples!

Greets,
Fabian