HOWTO?: tooltips for Gnome canvas items

[Jeremy Henty <jeremy chaos org uk>]

I'd like my application to have tooltips for individual Gnome canvas
items.  My approach is to set the tooltip for the canvas and enable
and disable it as the mouse passes over the items.  Provided I prod
the canvas with an event it *nearly* works.  But the tooltip appears
just beneath the bottom of the canvas, not at the item.  Can this be
worked around, or is this kludge just not going to work?

(Code attached but you'll need Ruby and ruby-gnome to run it.
Hopefully just reading it will make it clear what I'm doing; the
correspondence between the Ruby and Gtk APIs is straightforward.)

Cheers, 

Jeremy Henty 

#!/usr/bin/env ruby

#  An attempt to implement tooltips for Gnome canvas items by
#  attaching a tooltip to the canvas and enabling it and disabling it
#  as the mouse passes over the items.  We have to send an
#  enter-notify event to the canvas to get it to work.  But the tip
#  appears at the bottom of the canvas!  Aargh!

VERBOSE = true

require "gtk2"
require "gnomecanvas2"

def main
  Gtk.init
  Window.new.show_all
  Gtk.main
end

class Window < Gtk::Window
  def initialize
    super()
    set_title("Canvas Tips")
    signal_connect("destroy") do
      Gtk.main_quit
    end
    add(Canvas.new)
  end
end

class Canvas < Gnome::Canvas
  def initialize
    super()
    tips = Gtk::Tooltips.new
    tips.set_tip(self,"Canvas!",nil)
    tips.disable
    [ -50, +50, ].each do |x|
      [ -50, +50, ].each do |y|
        Splot.new(self,tips,x,y)
      end
    end
  end
end

class Splot < Gnome::CanvasEllipse
  def initialize(canvas,tips,x,y)
    radius = 5
    parameters = {
      :fill_color => "black", 
      :x1 => x - radius, 
      :x2 => x + radius, 
      :y1 => y - radius, 
      :y2 => y + radius, 
    }
    super(canvas.root,parameters)
    # return
    signal_connect("event") do |item,event|
      case event.event_type
      when Gdk::Event::Type::ENTER_NOTIFY
        tips.set_tip(canvas,"Item @ (#{x},#{y})",nil)
        tips.enable
        ev_new = Gdk::EventCrossing.new(Gdk::Event::Type::ENTER_NOTIFY)
        ev_new.window = canvas.window
        ev_new.x = x
        ev_new.y = y
        ev_new.put
      when Gdk::Event::Type::LEAVE_NOTIFY
        tips.disable
      end
    end
  end
end

main