Re: [Plplot-general] how to get size (in pixel) of a string ?

[Andrew R. <and...@us...>]

On Wed, Jan 13, 2010 at 12:51:13PM -0800, Alan Irwin wrote:
> On 2010-01-13 16:15+0100 Alain Baeckeroot wrote:
> 
> > Hi
> >
> > I would like to draw a box containing the legend of the graph, in a box
> > with semi transparent background. So i need to know the lenght
> > (in pixel or win coordinates) of the string, in order to size the box.
> >
> > I tried  `lenght = number_of_char(text) * 8 + 30; # pixels`
> > which does not work because the font is not fixed-width
> >
> > Is there a way to do do this ?
> 
> Hi Alain:
> 
> This is a most interesting topic.
> 
> As I recall, the high-level octave interface does have some legend
> functionality (you might want to take a look at its use in the "p"
> examples), but it has never worked very well because of the issue of string
> size. Would you be willing to try implementing some pllegend capability in C
> to see how well plstrl (mentioned by Arjen) satisfies the string-size
> requirements of pllegend?
> 
> Once we have a satisfactory pllegend implemented for our core C library,
> then it is straightforward to propagate it to all our languages including
> octave. That is also true of plstrl if there is any need for it beyond its
> internal use by the C version of pllegend.
> 
> My own feeling is that plstrl should give accurate results for our older
> drivers (e.g., xwin) that use Hershey fonts.  However, that accuracy might
> be as much as say 30 per cent off for our modern devices that use a large
> variety of different TrueType fonts accessible on various user platforms.
> So initially pllegend should probably be conservative about relying on the
> accuracy of the results from plstrl. Later on, it might be possible to
> upgrade plstrl to interrogate our various modern devices for the potential
> plotted size of the string argument to plstrl.  But we can deal with that
> issue later, and the interesting issue now is implementing a C version of
> pllegend that uses plstrl internally to estimate the plotted size of
> strings.
> 
> Alain, if you don't have the needed C skills and/or time to implement
> pllegend in C, let us know, and hopefully someone else will volunteer.

This would be good to see. It has long been on my wish-list. Ideally I 
would like to see an interface that supports colourbar support used
for filled contour plots for example as well as a key for identifying
different line / symbol styles. Alain, if you need any assistance I'll 
try and help you out. I'd suggest the first stage is to decide on a
suitable interface for this. 

I'd also suggest moving further discussion to the plplot-devel list. 

Andrew