We were forcing the size to be at least min-height, but we left the
baselines as they were, which had the effect of making text e.g
in entries 'stick to the top'.
With this change, we adjust the baseline to keep the ratio of
baseline to height unchanged.
Margins can be negative, and if we are not careful, then
content+padding+margin can end up with negative dimensions,
which can upset pixman and others. This commit ensures
that a gadget will not request or draw boxes with negative
dimensions, and get_border_allocation and get_content_allocation
will not return boxes with negative dimensions.
This fixes a crash in the paned separator drawing code that
can be reproduced by setting separator padding to 0.
https://bugzilla.gnome.org/show_bug.cgi?id=759657
As GtkCssNode has the visibility concept, it makes sense to mirror it in
gadgets.
Do what visibility does in widgets: Hidden gadgets can't be drawn or
allocated and request a 0x0 size.
Note that just like widgets, gadget visibility must not be changed in
size request, allocate or draw handlers.
GtkWidget::child-visible has no equivalent yet, code will have to
emulate that manually.
Empty boxes end up setting the clip to { 0, 0, 0, 0}, so warning
for a width or height of 0 triggers false positives. Instead,
initialize the clip to clearly invalid values.
A gadget is halfway between a widget and a CSS node. It's supposed to
provide the minimum convenicence around CSS nodes until we've figured
out how to integrate them with widgets.
