Bugs

 o I need to check the bounds are being calculated correctly so that they
   are correct for all zoom settings. Since cairo uses fixed point maths
   and I think only calculates up to a certain tolerance there might be
   slight errors in our gdouble results. So as the canvas is scaled this
   could eventually lead to the bounds being a pixel out, leading to painting
   errors. Maybe we should extend any bounds returned from cairo slightly to
   cover the maximum possible errors.

 o button press events are generating leave-notify and enter-notify signals.
   Seems to be a GTK+/X problem.

 o The GooCairo* types are used for some properties but aren't documented.
   Maybe we could point to the cairo docs.

Features definitely needed:

 o Editable text item - a port of GtkTextView.
 o Tooltips - I have code to support tooltips using the new API in GTK+ 2.12.

 o Need a function to setup a given cairo context with the defaults settings
   of a GooCanvas, e.g. default line width.

 o Check canvas and all items can be completely configured with properties
   so that GtkBuilder can be used to load hierarchies of items/models.
   Add "root-item" and "root-item-model" properties? Will GtkBuilder be able
   to handle the tree of items/models like that? What about GUI builders?
   How can gradients be specified by object properties?


Possible additional features:

 o Need a way to efficiently notify items about changes in canvas scale, if
   they request it. Could use something similar to the update flags.

 o Change GooCanvasStyle so it doesn't expose GValues in the API.
   Use get/set_boolean/int/double/boxed() instead.

 o Drag-and-Drop - probably copy all the GTK+ widget signals so items can
   implement their own behavior.

 o Caching of rendered items to improve performance. Items would have a cache
   option with choices like Never, Always and WhenVisible.
 o Sticky items that don't move at all as the canvas is scrolled & zoomed.
 o Filters like in SVG, to add graphical effects.
 o Support using the same item in different places, like SVG 'use'.
 o Support using system color names, like SVG, e.g. "ActiveBorder".
   This helps you write widget-like items that fit in with the rest of GTK+.
 o "scale-line-width" boolean property to specify if the line width scales
   with the canvas? The item bounds will change at different scale settings.
 o Arrows on path items, just like on polyline.


Requests from GTK+ people:

 o Use separate GooCanvasContainer[Model] interfaces? May help bindings.
 o GooCanvasWidget width & height are redundant - use widget's requested size.
 o Make PathCommand and LineDash structs opaque.
 o Use floating flag and sink() for objects.
 o Use 1-byte integer percentage for xalign/yalign instead of doubles?
 o Make it easy to add a border and background to items. "border-width",
   "border-color" and "background-color" properties? Might also need "x-pad",
   "y-pad", "x-radius", "y-radius" etc. Maybe have a related border item.
   Note that we only have the bounds in device coords, so drawing a border of
   a rotated item would be awkward. (Maybe we store the user bounds somewhere.)
 o Link/URL item, or enable URLs in the markup of text items.
 o A button item, with different children displayed for different states,
   maybe with optional automatic prelighting.