Re: Hacktext availability

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

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Dear Owen,

> Sorry if my responses here sound abrupt, I just don't have a lot of time
> to give detailed tutorials at the moment.

     No worries.  I can certainly understand time constraints.

     I think that maybe we are talking about two different things.  I
create text on the Gnome Canvas using

  item = gnome_canvas_item_new (group,
				GNOME_TYPE_CANVAS_TEXT,
				"markup",markup,
				"font-desc",description,
				"fill-color-rgba",dev->color,
				"x",0.,
				"y",0.,
				NULL);

and then request a magnification with

  gnome_canvas_set_pixels_per_unit(canvas,magnification);

One would expect the text to increase in size by the magnification (as is
the behaviour of gnome-print's Hacktext), but it doesn't.  I suppose that
I could scale pango text manually, but that isn't consistent with what is
expected on the Gnome Canvas.

     I have read the documentation that you suggested on
pango_context_set_matrix (), but can't understand how I would use this
information to fix the bounding box problem under rotations.  The code
snippet that I provided before rotates the text, but it is clipped by
an unrotated bounding box.  I have read the docs extensively, but there is
not enough information for me to understand why this is happening or
to change the behaviour.  I (and the plplot authors) would be very
grateful if you could point out how it is done.  The Hacktext api is not
public, and we would very much like to move to pango instead.

     With respect to shear transforms, I agree that I can just set the
matrices directly, and will do so in the future.

     I also agree that the documentation for the pango matrices is
sufficient.  However, it is helpful to have consistent standards for any
project:  I now have a mix of libart matrices (for GnomeCanvas),
PangoMatrix, and PLplot transformation matrices in a single Gnome project.
I think that this kind of complication uneccessarily adds complexity for
your end-user developers.  I'm not trying to be critical, but am just
trying to provide some (hopefully helpful) feedback here.

Sincerely,
Tom

- --

On Wed, 2 Mar 2005, Owen Taylor wrote:

> On Wed, 2005-03-02 at 18:27 -0400, Thomas J. Duck wrote:
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> > Dear Owen,
> >
> >      Thanks for your quick response.  I hope that you can appreciate that
> > I am trying to contribute, and have come to this list to see if I can get
> > some help with a problem that I have been struggling with for some time.
> > It's not like I'm a novice programmer.  The questions may sound dumb to
> > you, but there are many others struggling with the same problems (google
> > "gnomecanvas rotate text" if you like).
>
> Pango support for rotation is quite recent (last fall), so I'd expect
> most responses to that search to be older.
>
> Sorry if my responses here sound abrupt, I just don't have a lot of time
> to give detailed tutorials at the moment.
>
> >      I am a developer with the plplot project, and have recently written a
> > driver for it that can be used to imbed plots in Gnome applications.  I
> > have all of this working using gnome-print's Hacktext, but as Jody has
> > explained to me, moving to pango (if possible) would be best.
> > On Wed, 2 Mar 2005, Owen Taylor wrote:
> > > Pango supports shears. Pango handles bounding box rotations. Pango
> > > scales under zoom. I think you have some difficulty in your code.
> >
> >      When I zoom in with GnomeCanvas, the text doesn't scale.  Maybe
> > pango supports scaling, but it's not happening for me on the Canvas,
> > although Hacktext scaling works fine.  There is no pango_matrix_shear
> > function to go along with pango_matrix_rotate et al (at least not in
> > Debian sid).
>
> Why would you construct the matrices that way? Don't you need to
> match the matrices that the gnome-canvas is passing to you?
> There is no pango_matrix_shear() because I don't consider it to be
> a common or useful user operation, but you can always construct
> a PangoMatrix that shears.
>
> >  And, despite reading the available documentation and
> > searching the Web, I can't figure out how to fix this bounding box
> > problem.
>
> I think the statement I made earlier that the extents reported by
> Pango are in user-space (before transformation) coordinates is
> all you need to fix that problem. This is documented in the
> docs for pango_context_set_matrix()
>
> >      I would appreciate it if you could provide me with some pointers, and
> > have provided a code snippet to that end.  If I haven't given you enough
> > information, please let me know and I will elaborate where needed.
> >
> > > >      BTW, I am surprised that pango isn't using libart for the matrix
> > > > calculations, considering that this is a Gnome project.  Needless
> > > > complication, no?
> > >
> > > Why would I pull in a moderately large, hard to use, scheduled-to-be-
> > > replaced library to avoid what ended up being 160 lines of code
> > > including documentation?
> >
> >      Because standardization is good.  Libart is well documented, and I
> > have had no problems using it.  It would be better for the end-user
> > application developers like myself if you stuck with the standard until it
> > is replaced.
>
> And PangoMatrix is not documented? You have found the Pango docs at
> http://developer.gnome.org/doc/API/2.0/pango/, right? (Probably
> also installed on your system.) While I wouldn't claim they are great,
> PangoMatrix is definitely documented there.
>
> There is nothing standard about libart. Honestly, it's a bit of a horror
> of a library in many ways. There is no way I'd have made it a dependency
> of Pango. There is no *conceivable* way I'd have made it part of the
> public Pango API.
> 						Owen
>
>

- --
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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