Re: Invisible GtkImage

[Andrew Potter <agpotter gmail com>]

On Thu, Jun 13, 2013 at 8:42 PM, Kip Warner <kip thevertigo com> wrote:

> That makes sense, but should the allocation passed to the base class's
>  do_size_allocate() be the original allocation parameter that was passed
> into the override, or the one that I modified to contain the new image
> dimensions adjusted to maintain the aspect ratio?
>
> If I use the allocation passed into the override, the pixels in the
> image appear to rescale appropriately, but the image as a whole does
> not. It grows horizontally, but the height of the widget remains fixed.


Yes, you should pass in the same allocation you received. A really proper
way to do this would be to scale the image to less than the full allocation
depending on the margins/padding/border etc., and then the base class could
do the right job with honoring that stuff after you set the pixbuf. But by
default that stuff is 0 and you don't have to worry about it in this case.

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.

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.

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.