From: Josef Wolf <jw@...>
Date: 2009-09-12T04:00:13+09:00
Subject: Re: How to bind canvas events to tags?

On Sat, Sep 12, 2009 at 02:23:30AM +0900, Joel VanderWerf wrote:
> Josef Wolf wrote:
>> BTW: do you have a description of the "%x %y" formatting specification?
>
> http://www.tcl.tk/man/tcl8.4/TkCmd/bind.htm#M41

Ough. Every time I think I get closer (remember? I am trying to implement
a zoomable canvas), I find there is a lot more work to do :-()

My first attempt to adopt event handling to the zoom operation was like
this:

  class TkEvent::Event
    # FIXME: need a better name than "nonzoomed". Recommendations?
    attr_accessor :x_nonzoomed, :y_nonzoomed
  end

  class TkZoomCanvas < TkCanvas
    def itembind(tag, ev, cb)
      super(tag, ev, proc{ |e|
              if e.x then e.x_nonzoomed = e.x/@zoom ; end
              if e.y then e.y_nonzoomed = e.y/@zoom ; end
              cb.call e
            })
    end

    def bind(ev, cb)
      # looks similar to itembind
    end
  end

Now, itembind (and bind?) seem to accept various forms:

  1.  canvas.itembind("mytag", "1", proc{|e| ... })
      This form works fine with above code

  2.  canvas.itembind("mytag", "1", "%x %y") {|x, y| ... }
      In this case, I will have to build the argument list. Seems to be a
      tedious task. Maybe there already exist a Tk method I could use to
      build that list?

Are this the only two existing forms?