Re: What is "is_pointer_event" in goo_canvas_get_item_at ?

[Brandon Lewis <brandon_lewis berkeley edu>]

Till Harbaum / Lists wrote:
> Hi,
>
> thanks to your help, my mapping application now runs with goocanvas 99% like it did with
> gnomecanvas. The only difference is that goocanvas clips the entire view to the bounds which
> i actually like. I still have to test run it on the n810 being my primary target and see if the 
> performace of goocanvas is sufficient.
>
> I discovered that i have to set is_pointer_event to TRUE so that goo_canvas_get_item_at only
> returns polylines if you are actually on those lines. If i set it to FALSE polylines also are returned
> if the given coordinate is within the area sourrounded by the polyline. Why is that? The
> documentation also isn't very helpful:
>
> is_pointer_event: TRUE if the "pointer-events" property of items should be used to determine 
> which parts of the item are tested.

It seems like you understand it pretty well. pointer-events is a gobject 
property of all canvas items. It controls how goocanvas determines whether the 
pointer is "inside" a canvas item. When false, the event coordinates must only 
be within an object's bounding box. When true, the event coordinates must be 
within the object's path (it's shape). Try an experiment:

* create a goocanvas.Canvas with a goocanvas.Polyline object inside of it.
* connect to the mouse-enter and mouse-leave signals of ** the Polyline **, not 
the canvas:
* on mouse-enter, make set stroke_color to "orange"
* on mouse-leave, make set stroke_color to whatever color it was originally

First try it with the polyline's pointer-events property set to True. Then try 
it with the pointer-events property set to false, and note the difference. All 
pointer events are affected by this property: button-press, button-release, 
motion-notify, etc.

So, in some situations you want to find out what object is at (or near) 
arbitrary x,y coordinates. The is_pointer_event parameter controls how goocanvas 
should go about determining whether or not an arbitrary point is within an 
object. It works just like the pointer-events property.

> Can anyone explain this?
>
> Thanks so far,
>   Till
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