Re: GtkCanvas requirements?

[Havoc Pennington <hp redhat com>]

Hi,

Carlos Garnacho wrote:
> What are we missing in the current core? What benefits would bring a new
> one?

I certainly have not sat down and exhaustively tried to figure this out.

There is a fair bit of cruft in the core; if you were starting over, I'm 
sure you'd want to just kill GdkWindow for example, and many other "Xlib 
leakages" such as how some of the events work.  You'd want to be 
Cairo-only, use interfaces instead of objects for the core APIs (widget, 
container), rethink GtkContainer and its common subclasses (as 
HippoCanvas does), fix the theme system, blah blah. The list could get 
pretty long.

The question is which of these are cosmetic cleanups that aren't really 
worth it and which add new capabilities, and how long is the new 
capabilities list. Probably not nearly as long as the cosmetic list.

Replacing the core with a more canvas-ish solution would not have to be 
done all in one shot, though; the WidgetCanvasItem and CanvasWidget 
provide a lot of interoperability. You could also have some of the 
existing widgets implement the CanvasItem interface directly, for 
example GtkEntry could be both a GtkWidget and a CanvasItem.

There's no real disruption to the current core while building a new 
canvas-style core either, in fact I'd suggest evolving the canvas stuff 
outside of GTK+ for at least a couple of years. It is probably also true 
that certain "heavy" widgets such as TextView and TreeView never benefit 
from conversion to a canvas-like model.

New capabilities I can quickly think of, all of which might be possible 
to retrofit into GtkWidget/GtkContainer themselves:
 - better layout
 - overlapping/alpha-blending
 - reduced overhead / more lightweight objects (speculative)
 - better containers replacing [HV]Box/Misc (see HippoCanvasBox and
   xalign, yalign, padding, border properties)
 - printing trees of items
 - general ability to draw an item to stuff other than the screen
 - support for nonrectangular items (e.g. a diagonal line)
 - nicer event system (e.g. easier enter/leave tracking, remove
   only-useful-for-toplevels stuff from main item interface)

In the end I'm guessing this is just too much work. At the same time, 
for some apps already we see that even a simple answer like HippoCanvas 
has important advantages over GtkWidget.

Havoc