Re: Generic positioning

[Damon Chaplin <damon karuna eclipse co uk>]

On Wed, 2008-10-29 at 16:06 +0100, Armin Burgmeier wrote:
> On Wed, 2008-10-29 at 12:37 +0000, Damon Chaplin wrote:

> > I'll accept a patch that adds x, y, width & height properties to most of
> > the items that don't have them, with functionality as in your latest
> > patch. I don't want to add x, y, width & height properties to the
> > GooCanvasItem interface though.
> > 
> > For GooCanvasGroup I'd prefer it if the x & y properties set the origin
> > of the existing transformation matrix rather than adding an extra
> > translation.
> 
> Wouldn't this make it impossible to get back the x and y properties in
> get_property() then? I mean, if the group is translated via
> goo_canvas_item_translate, then this should not add up to the x & y
> properties (to behave the same was as GooCanvasRect, for example),
> should it?

The group has no real x & y properties, so we are basically just
modifying its transformation matrix anyway.

I thought it would be better if we made that clear, rather than try to
explain that the x & y properties are an extra translation applied after
the group's transformation matrix.


> >  I'm not sure about adding width & height though - I'd
> > prefer not to. (Your code for GooCanvasGroup looks wrong as it uses
> > goo_canvas_item_get_bounds() to get the child extents, but the bounds
> > are in device space so may have arbitrary transformations on them.)
> 
> What code do you mean exactly? I added test code for the group width &
> height to generic-position-demo.c, and everything behaves as I'd expect,
> I think.

goo_canvas_group_get_extent() is wrong. If the group or one of its
ancestors was rotated all of the child bounds would change (since they
are in device space). So the new "width" and "height" properties of the
group would change. But that is inconsistent with all the other items,
whose width and height remain constant when rotated.

I don't think there is a way for a group to get the bounds of child
items in its own coordinate space.

Damon