It's useful to set a slice size != border-width, as backgrounds are
clipped to border-width too.
As slices can be half-transparent and overlap the background,
this would not fill the border box properly if we only use a single
property for specifying the width.
Also, this brings us even closer to CSS3.
It's a custom property with the same semantics of text-shadow, which
works on icons and icon-like UI elements, such as spinners, arrows and
separators.
It's an entry, so it already has a background below, even when the entry
doesn't have a frame. Also, gtk_spin_button_draw_arrow() will render a
background and a frame in the arrow space anyway.
NULL is a valid value for border-image, so if it's NULL when unpacking,
don't try to access the struct fields, but just init the GValues for the
unpacked parameters.
The new code is smaller, less crashy and correct(er), but arguably more
complex. I'd have liked to make it simpler, but this border image
algorithm is complex...
It's not useful to cache these surfaces here, as the GtkBorderImage will
be always generated on the fly, being a shorthand property.
This also allows to get rid of the intermediate image surfaces for
rendering the slices; we now use cairo_surface_create_for_rectangle()
to proxy the slices from the source surface to the rendered area, which
should also yield better performance.
It's composed by
- border-image-source: a cairo_pattern_t holding an image from file or a
gradient
- border-image-slice: a GtkBorder containing the slice offsets to apply
on the image
- border-image-repeat: a GtkRepeatType for the image
We deviate from pure CSS3 in the following ways:
* border-image-width is assumed to be always 1, i.e. always equal to
what's specified by border-width. I don't think it's a particularly
useful property to have, but we could add it later if needed.
* border-image-outset is absent, as we can't render outside of the
allocation yet.
https://bugzilla.gnome.org/show_bug.cgi?id=651194
It seems to be very broken wrt input handling, causing random icons to
light up etc.
So until this is fixed, better remove composite support. It only removes
animations, so it's not a big loss for functionality.
