Re: Invisible GtkImage

[Kip Warner <kip thevertigo com>]

On Thu, 2013-06-13 at 21:32 -0700, Andrew Potter wrote:
> What you can't do is allocate additional height to yourself in
> do_size_allocate(). So if you have a short wide image and are allocated
> more width than the height at your aspect ratio allows, you _shouldn't_
> scale up or else your image will be clipped; the toolkit knows what it
> allocated to you and will not let you draw outside of that region.

Ok, fair enough.

> What you can do to (try to) prevent that situation is to set the widget to
> do "height for width" allocation, and override
> get_preferred_height_for_width() to honor your aspect ratio. In some
> situations of course the toolkit won't be able to perfectly honor the
> allocation request, so be sure not to scale out of bounds no matter what.

Right. What I will do is resize to exactly what is passed into my
do_size_allocate() override since that size should theoretically meet
the aspect ratio I am maintaining via my
do_get_preferred_height_for_width() override.

> I'm not sure on how to set the widget to do "height for width" allocation,
> it seems you may have to override get_request_mode()? What I did was
> override all the size request methods instead.

Here's what I did...

    def do_get_preferred_height_for_width(self, width):
        return (width / self._aspectRatio)

    def do_get_request_mode(self):
        return Gtk.SizeRequestMode.HEIGHT_FOR_WIDTH

...but something very interesting happens immediately after the return
in do_get_preferred_height_for_width(). I get an assertion fail buried
deep somewhere in python-gi...

        ERROR:../../gi/pygi-closure.c:494:_pygi_closure_set_out_arguments: code should not be reached

One thing is clear. The latter do_get_request_mode() is in fact being
queried.

-- 
Kip Warner -- Software Engineer
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http://www.thevertigo.com