Re: PyDia and Metapost

[Lars Clausen <lars raeder dk>]

On Wed, 2006-02-15 at 12:55 -0500, Rob McDonald wrote:
> > However, the vertical positioning still seems to be off by about the
> height
> > of a lower case letter.  Baseline vs. character center.
> >
> >              Rob
>
> In render_metapost.c , in the function draw_string , there is a switch based
> on Dia's alignment parameter.  The comment says
>
> /* We use the "top" modifier to MetaPost's alignment because Dia draws
>  * text _above_ the point at which the text is "located".  */
>
> (sorry I don't have a line number, I'm browsing source in the online CVS.)
>
> Consequently, the code uses the MetaPost commands
>
> label.urt
> label.top
> label.ulft
>
> For right, center, and left aligned text.  This would appear to be the right
> thing to do.
>
> However, when you position text in a box, it comes out wrong.  Manually
> editing the *.mp file and replacing the above strings with
>
> label.rt
> label
> label.lft
>
> Gives the behavior I'd like to see (very close to where it appears on the
> Dia screen.)

It's close, but not quite there, as text in Dia is rendered (from a
renderer point of view) at the baseline of the text, not the center, top
or bottom.  You can see in lib/diagdkrenderer.c how we get the text
ascent (unfortunately not a simple operation for raw text) and adjust
the y-pos for that to get the rendered rectangle.  I hope to get around
to doing a draw_text_line for metapost.

-Lars