matplotlib-devel Mailing List for matplotlib

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    Darren> I just noticed that the following script generates a
    Darren> diagonal line that looks like it was drawn with a really
    Darren> unsteady hand:

    Darren> from pylab import frange, plot, show
    Darren> plot(frange(-1,1,.01)*1e10) show()

    Darren> The problem is not noticable for a small number of points,
    Darren> such as plot(frange(-1,1,.5)*1e10). I tried clearing
    Darren> site-packages, rebuilt MPL-0.80, the problem appears to be
    Darren> in CVS.

w/o testing, I'll hazard a guess that this is due to a workaround I
have never been able to figure out with how agg does subpixel
rendering

Try commenting out these lines in _backend_agg.cpp in the draw_lines
function

    thisx = (int)thisx + 0.5;
    thisy = (int)thisy + 0.5;

These lines snap all the x and y points to pixel centers.  If you
don't use pixel centers, agg will draw lines of different widths and
heights depending on the subpixel fraction.  This is only apparent for
vertical and horizontal lines, generally, but is glaring for ticks and
grid lines.  In the past, I've added a hack to only do snap to pixel
for horizontal and vertical lines with 2 points, which fixes the
special case problems of ticks and grids

I raised this issue with Maxim on the agg mailing list

http://sourceforge.net/mailarchive/message.php?msg_id=8575544

and he responded by writing this page

http://antigrain.com/tips/line_alignment/line_alignment.agdoc.html

which I still haven't been able to digest sufficiently in a way that
fixes this problem generally.

I reinstated in CVS a temporary hack which only does the snapto pixel
trick for len(2) lines.  Should work well for most use cases.  Give it
a try.

JDH

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    Darren> On a related subject, tex layout via text.usetex does not
    Darren> appear to be working at the moment. I tried undoing my
    Darren> changes but was not able to get the old results back. Did
    Darren> I break this or did I catch it in transition?

This is totally experimental and will break all backends except agg --
I will handle this more elegantly once I figure out how I want to do
it, but right now am trying to fix low level problems like getting the
alpha channel right (am working with dvipng author for the next dvipng
release to get proper access to alpha channel) and then to handle
rotation.  Once all of that is working I can work out the interface so
that it plays nicely with other backend.

With the revision I just checked into CVS, you should get TeX rasters
in agg if you set usetex (they will look crappy because of the alpha
problem).  But I'm optimistic that I can clear up all these problems
in a couple of weeks time.  If you get psfrag in decent shape, we'll
be in good shape for a TeX enabled 0.81 release...

    Darren> The horizontal placement appears to be fixed in CVS. I
    Darren> haven't gone searching for trouble in the vertical layout
    Darren> yet.

Unless you fixed it, I would be surprised...

JDH

I just noticed that the following script generates a diagonal line that loo=
ks=20
like it was drawn with a really unsteady hand:

from pylab import frange, plot, show
plot(frange(-1,1,.01)*1e10)
show()

The problem is not noticable for a small number of points, such as=20
plot(frange(-1,1,.5)*1e10). I tried clearing site-packages, rebuilt MPL-0.8=
0,=20
the problem appears to be in CVS.

Darren

I played with the new latex backend tonight, and made some incremental=20
improvements. texmanager now calls latex instead of tex, so we can make use=
=20
of some of the more complex layout commands, \frac{}{} for instance. A new=
=20
version of tex_demo.py is in cvs, try running:

>   > python examples/tex_demo.py -dLaTeX
>   > latex tex_demo.tex
>   > dvips -o tex_demo.ps tex_demo.dvi
>   > ggv tex_demo.ps

On a related subject, tex layout via text.usetex does not appear to be work=
ing=20
at the moment. I tried undoing my changes but was not able to get the old=20
results back. Did I break this or did I catch it in transition?

>
> There are a few problems
>
>   * the page width and figure placement in the latex document are off
>     center
>
>   * the text color is not being respected
>
>   * to get the width and height of the string, I tex the individual
>     strings separately, run dvips on them, and get the bounding box
>     from the generated file.  This all happens with caching in
>     matplotlib.texmanager.  Right now the fontsize is being ignored in
>     this process so the layout will be off for nonstandard font sizes
>     -- anything other than the default design size of latex which
>     defaults to 10pt I think.

The horizontal placement appears to be fixed in CVS. I haven't gone searchi=
ng=20
for trouble in the vertical layout yet.

>
>   * the text doesn't scale right if you provide a size arg to
>     includegraphics, eg [width=3D4.in]


Darren