Re: Hacktext availability

["Thomas J. Duck" <tomduck fizz phys dal ca>]

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Hi Jody,

On Fri, 25 Feb 2005, Jody Goldberg wrote:
> There are two simple approaches.
> 1) Use the existing affine support in gnomecanvas to rotate the
>    text.  It's not perfect but it works.
> 2) Use the new pango-1.8 level apis
>     pango_context_get_matrix (context);
>     pango_matrix_rotate (&rotmat, rv->rotation);
>     pango_context_set_matrix (context, &rotmat);
> in gnomecanvas.

     I have implemented each of these approaches, and there continue to be
important problems with pango on the Gnome Canvas.  So, I am leaning
toward copying your Hacktext code into plplot.  Don't get me wrong: I
would be happy to move to pango, but as far as I can tell it cannot do
what your Hacktext already does.

     For example, a shortcoming of pango on the Gnome Canvas is that it
does not scale under a zoom.  Also, shear transformations aren't
implemented in the pango api.  Hacktext scales and shears very nicely.  On
the other hand, Hacktext can't process markup text like pango, and that
would be a very nice feature to have.  Please correct me if these
understandings are wrong.

     Rotations with pango on Gnome Canvas continue to be troublesome, but
Hacktext rotates nicely.  Using pango, I can get the glyphs to rotate, but
the text is clipped according to some unrotated bounding box.  Argh!  Here
is my code snippet for rotations under pango:

  context = pango_layout_get_context(GNOME_CANVAS_TEXT(item)->layout);

  matrix = PANGO_MATRIX_INIT;

  pango_matrix_rotate(&matrix,90.);

  pango_context_set_matrix(context,&matrix);

  pango_layout_context_changed(GNOME_CANVAS_TEXT(item)->layout);

Reading the available documentation and lots of raw code hasn't shed any
light on a solution to the clipping problem.  Any ideas?

     BTW, I am surprised that pango isn't using libart for the matrix
calculations, considering that this is a Gnome project.  Needless
complication, no?

     I appreciate your help with this, and I am sure others will too if we
can resolve the text transformation problem.

Sincerely,
Tom

- --
Thomas J. Duck <tomduck fizz phys dal ca>

  Department of Physics and Atmospheric Science, Dalhousie University,
    Halifax, Nova Scotia, Canada, B3H 3J5.
  Tel: (902)494-1456 | Fax: (902)494-5191 | Lab: (902)494-3813
  Web: http://aolab.phys.dal.ca/~tomduck/
  Public key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x17D965DB
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