RE: Metapost - text alignment

[Lars Clausen <lars raeder dk>]

On Wed, 2007-01-31 at 11:19 +1030, Young, Robert wrote:
> > > Hmmm, my only testing has been with the test documents 
> > attached to the 
> > > bug 332544. Do you have a simple example you could send me or attach 
> > > to the bug report and I'll get it to work too?
> >
> > It is hardly worth posting an example.  Just create some text 
> > in cmr10 and set the size to 0.35.  If your change makes it 
> > output 'scaled 0.67'  (approximately 2.05/3.0) then we have a 
> > problem.  If it still outputs 'scaled 1.05' then everything is normal.
>
> OK, I've updated the test cases attached to the bug 332554
> http://bugzilla.gnome.org/show_bug.cgi?id=332554 (sorry for getting the
> number wrong before)
>
> The new test case has cmr, serif, sans and monospace. As a result I've
> updated the patch to try to fit those font sizes.
>
> Unfortuntely there seems to be such a difference in the fonts used that
> the scaling is quite different for them all. I like Lars' idea of
> getting LaTex to fit the text to the given width using kerning, but it's
> just so way out at the moment that this will cause problems. Maybe the
> font name matching needs improving instead?

Is it really so way out?  I added a patch to the bug that uses text_line
to get the right width and do a \makebox for it.  It seems right to me,
but mptopdf complains.  Obviously, it needs to not use the calculated
scale factor, and there may be a different scale factor involved instead
(0.7 seems to be common:), but I want to see if text_line can be made to
work.  Test on the samples/render-test.dia file, it has text that will
be rendered with the text_line bit.

> As an aside, I note that the error in the text scaling is non linear -
> it changes depending on the font size. This seems to be a font dependant
> characteristic - it occurs in Dia and MetaPost. The attached example has
> font size 2, 1, 0.5, 0.25 for three font styles. The .png shows what it
> looks like in Dia, and .pdf via metapost export (with the latest patch
> to bug 332554).

And that is *exactly* why we need text_line.  Even in GTK land, text
scaling isn't linear, it's even worse in TeX land because of the fine
typesetting.

-Lars